An Information Theoretic Evaluation Criterion for 3D

Reconstruction Algorithms

Rama Chellappa Amit K. Roy Chowdhury

University of Maryland, University of California

College Park, MD 20742. Riverside, CA 92521.

rama@cfar.umd.edu amitrc@ee.ucr.edu

Abstract

Even though numerous algorithms exist for estimating the structure of a scene from its video, the solutions

obtained are often of unacceptable quality. To overcome some of the deficiencies, many application systems rely

on processing more information than necessary with the hope that the redundancy will help improve the quality.

This raises the question about how the accuracy of the solution is related to the amount of information processed

by the algorithm. Can we define the accuracy of the solution precisely enough that we automatically recognize

situations where the quality of the data is so bad that even a large number of additional observations will not yield

the desired solution? This paper proposes an information theoretic criterion for evaluating the quality of a 3D

reconstruction in terms of the statistics of the observed parameters (i.e. the image correspondences). The accuracy

of the reconstruction is judged by considering the change in mutual information (or equivalently the conditional

differential entropy) between a scene and its reconstructions and its effectiveness is shown through simulations.

A brief discussion on the applicability of information theoretic criteria for other vision algorithms concludes the

paper.

1 Introduction

Obtaining accurate 3D models from video using the structure from motion (SfM) approach [1], [2], is extremely important because of its diverse applications, ranging from multimedia to medical diagnosis. Yet the quality of many of

the automatic 3D reconstructions leave much to be desired. This has led many researchers to analyze the sensitivity,

robustness and statistical error characterization of the existing algorithms, trying to understand algorithm behavior

and the characteristics of the natural phenomenon that is being modeled [3], [4], [5], [6], [7], [8], [9]. To overcome

these errors, the tendency has been to add redundancy in the information processed. This raises the question as to

how the redundant information affects the quality of the final solution. In this paper, we consider the situation where

multiple reconstructions of the same scene are available (called intermediate or individual reconstructions, in this

paper), that are combined together to obtain the final estimate (Figure (1)). We compute the incremental mutual

information between the unknown 3D structure and increasing numbers of intermediate reconstructions.

Before proceeding to give a detailed description of the idea, we would like to draw the attention of the reader

briefly to the area of model selection in statistics (AIC, BIC, MDL etc. [10]). The idea of fitting models to geometric

data was formalized by Kanatani using a Geometric Information Criterion (GIC) [11]. However, a large number of

SfM algorithms are not model based; they reconstruct individual point features of the scene. Our work tries to define

the quality of reconstruction from point features in information theoretic terms. We also provide a discussion on the

usefulness of information theoretic measures for evaluating computer vision algorithms.

1

Proceedings of the 2004 Performance Metrics for Intelligent Systems Workshop.

NIST Special Publication 1036

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.SP.1036
 X

 X

.

.

.

.

.

.

.

X

Individual

Reconstruction

Individual

Reconstruction

H(1)

 H(L)

Algorithm

 Fusion

Figure 1: Block diagram representation of the reconstruction framework. X is the inverse depth that we want to estimate, (H(1), ..., H(L))

are the intermediate reconstructions (e.g. from each individual camera), and Xˆ is the final fused estimate.

2 An Information Theoretic Criterion for 3D Reconstruction

2.1 Problem Formulation

We assume that all the depth values are aligned to a common frame of reference. Feature points will be represented

by subscripts, separate reconstructions will be within parenthesis. The vector of estimates of the inverse depth 1

[Hi(1), ..., Hi(N)]0 will be denoted by H

(N)

i

. The boldface notation H(i) will represent all the features in the i

th

reconstruction. The final estimate Xˆ of X = [X1, ..., XM ]

0

is obtained by fusing the individual reconstructions

(H(1), ..., H(L)). To keep the notation simple, the subscript for the feature point will not be mentioned, unless

required. The individual estimates are modeled as

H(i) = X + V (i) (1)

where X is the inverse depth value of the particular feature.

2.2 Main Result

We will now present an information theoretic measure for evaluating the quality of a 3D reconstruction algortihm by

analyzing the contribution of each of the individual reconstructions. Our entire analysis is for a particular point and

thus the subscript will be dropped, unless required for clarity. Our criterion for evaluating the quality of reconstruction depends on estimating the difference in mutual information for the two sets of observations, H(L)

and H(L−1).

We term this as the incremental mutual information (IMI), i.e.

∆I(L) = I(X, H(L)) − I(X, H(L−1)). (2)

The term gives us an idea of the contribution of the L

th observation to the reconstruction strategy with respect to the

previous (L − 1) observations. As the number of observations increase, the effect of an additional observation decreases and approaches zero in the limit. In order to be assured that the reconstruction quality is actually improving,

we need to consider only those situations where the mutual information I(X, H(L)) is non-decreasing. This ensures

that we remove cases where the reconstruction is actually getting worse, and further observations are not improving

it any more.

Using the relationship between mutual information and entropy, it is possible to obtain a different interpretation

of the IMI. Denoting by h(X) the entropy of the random variable X, we know that [12] I(X; Y ) = h(X)+h(Y )−

h(X, Y ). Thus ∆I(L) in (2) can be written as

∆I(L) = I(X; H(L)) − I(X; H(L−1)) = h(X|H(L−1)) − h(X|H(L)). (3)

The quantity defined as the IMI can also be referred to as the incremental conditional entropy. Since entropy of a

random variable is a measure of its uncertainty, ∆I measures the reduction in the uncertainty as we add an extra

1The inverse depth is used throughout this paper since it is the quantity that is estimated from the SfM equations for reconstruction from a

video and its statistics can be obtained in an analytic form more easily than for the depth.

2
observation. Since the IMI tends to zero in the limit, the difference in the conditional entropy also approaches zero.

Thus we will consider more and more images from the video sequence till the uncertainty in the final structure

estimate can be reduced no further. This is the intuitive idea behind our criterion in (2).

The rate at which the IMI decreases is also an important measure of the progress of the algorithm. An extremely

slow rate of fall indicates that more images will be necessary to achieve an acceptable level of quality. Since there

is motion between adjacent frames of the video, a particular point will move out of the field of view of the camera

after a certain amount of time. A very slow rate of fall of ∆I might mean that the quality of the reconstruction is not

good enough even when the point is no longer visible. The rate of change of ∆I can be obtained as

∆2I(L) = ∆I(L) − ∆I(L − 1)

= I(X, H(L)) + I(X, H(L−2)) − 2I(X, H(L−1)). (4)

Combining (2) and (4), we can state that an acceptable reconstruction quality has been achieved when I(X, H(L))

is non-decreasing and the following conditions are satisfied simultaneously:

∆2I(L) ≤ 0, ∀L > L0,

∆I(L) < τ, (5)

where L0 is a constant and τ is a threshold defining an acceptable quality of reconstruction. Since ∆I(L) is monotone non-increasing for L > L0 and is bounded below by zero, the monotone convergence theorem [13] applied to

(3) implies that h(X|H(L−1)) → h(X|H(L)) → h0 for some L > L0. Thus, h0 is the minimum level of uncertainty

in a scene described by L observations.

Since the criterion does not depend on how the intermediate reconstructions are obtained, it is, in principle,

independent of the 3D reconstruction strategy. However, the procedure for estimation of IMI may be optimized for

a particular algorithm. Details on the estimation process can be found in [14].

2.3 IMI Computation Under Gaussian Distributions

Assume that X ∼ N (0, σ

2

x = PX) and {V (i),i = 1, ..., N} is a sequence of independent random variables

distributed as N (0, σ

2

V (i)

). Let PV = diag [PV (i)]i=1,...,N = diag hσ

2

V (1), ..., σ

2

V (N)

i

2

.

From (1), E[H(i)] = 0 and

E[H(i)H(j)] = E[(X + V (i))(X + V (j))]

= PX + PV (i)δij , (6)

where δij is a Kronecker delta function. Thus the covariance of H(N)is PH(N) = P

(N)

V + 1N PX1

T

N , where 1N is

a vector of N ones. Then the mutual information between X and H(i),

I(X; H(i)) = h(H(i)) − h(H(i)|X)

=

1

2

log 1 +

PX

PV (i)



. (7)

Next, consider the mutual information between the unknown X and the vector of observations H(N). We will denote

by |K| the determinant of a matrix K.

I(X; H(N)) = h(H(N)) − h(H(N)|X)

(a)

= h(H(N)) −

X

N

i=1

1

2

log(2πePV (i))

(b)

=

1

2

log 

|PV + 1N PX1

T

N |

|PV |



. (8)

2Where necessary to distinguish a particular feature point, we will use the notation σ2

xj

and PVj

(i) or σ

2

Vj (i)

for the j

th point.

3
(a) is a result of applying the chain rule of entropy and substituting the expression for the differential entropy

of a Gaussian random variable [12]; (b) is due to the fact that |PV | =

QN

i=1 PV (i) =

QN

i=1 σ

2

V (i)

. Using the

method of induction and the properties of determinants, it can be shown that |PV + 1N PX1

T

N | =

QN

i=1 σ

2

V (i) +

σ

2

x

PN

i=1

QN

j=1

j6=i

σ

2

V (j)

. Then from (8), the expression for the mutual information becomes

I(X; H(N)) =

1

2

log 1 +

X

N

i=1

σ

2

X

σ

2

V (i)

!

. (9)

Let us compute the difference in the mutual information for the two sets of observations, H(N)and H(N−1). We

shall call this the incremental mutual information, ∆I. Thus,

∆I = I(X; H(N)) − I(X; H(N−1))

=

1

2

log 

|PV (N) + 1N PX1

T

N |

|PV (N−1) + 1N−1PX1

T

N−1

|

.

|PV (N−1) |

|PV (N) |

!

=

1

2

log





QN

i=1 σ

2

V (i) + σ

2

x

PN

i=1

QN

j=1

j6=i

σ

2

V (j)

QN

i=1 σ

2

V (i) + σ

2

x

PN−1

i=1

QN

j=1

j6=i

σ

2

V (j)





=

1

2

log



1 +

1/σ2

V (N)

1

σ2

x

+

PN−1

i=1

1

σ

2

V (i)





=

1

2

log



1 +

1/PV (N)

1

σ2

x

+

PN−1

i=1

1

PV (i)



 . (10)

Equation (10) gives us a measure of the extra information that would be obtained by including an additional observation into the fusion process. Also, since

I(X; H(N)) − I(X; H(N−1)) = h(X|H(N−1)) − h(X|H(N)), (11)

the quantity defined as the incremental mutual information can also be referred to as the incremental conditional

entropy. Thus we are measuring the reduction in the uncertainty of the solution as we consider an extra observation.

The difference in the differential entropy determines the decrease in the coding length of the scene structure as the

number of observations increases [12].

The above calculation requires computing the variances of the intermediate reconstructions. Any method to

compute them is perfectly suitable. In an earlier work [15], we have shown how to do this for the case of 3D reconstruction using optical flow. It should be remembered that all the geometric quantities have to be with respect to a

particular frame of reference; hence it may be necessary to transform the variances appropriately.

An Estimation Theoretic Interpretation: We will now present an alternative interpretation of the result in (10)

from an estimation theoretic perspective. The mean squared distortion is defined as

D(X, Xˆ ) =

1

M

X

M

j=1

E[(Xj − Xˆ

j )

2

]. (12)

Let p(Xj , Hj (1), ..., Hj (N)) denote the joint density function of the parameter and observations. The mean square

error estimator Xˆ

j of Xj , obtained from H(N)

, is Xˆ

j (N) = E

h

Xj |H

(N)

j

i

. From the Cramer-Rao lower bound

4
(CRLB) we can write the following set of inequalities.

D ≥

1

M

X

M

j=1

1

E



−

∂2

∂X2 log p(Xj , Hj (1), ..., Hj (N))

=

1

M

X

M

j=1

1

1

σ2

xj

+

PN

i=1 E



−

∂2

∂X2 log p(Hj (i)|X)



≥

1

1

M

PM

j=1 

1

σ2

xj

+

PN

i=1

1

PVj(i)



4

=

1

1

M

PM

j=1

1

Dj (N)

. (13)

The last step is a result of the application of Jensen’s inequality [16] and the fact that E

h

−

∂

2

∂X2 log p(Hj (i)|X)

i

=

1

PVj(i)

. Recalling that (10) is for a particular feature point where the subscript has been suppressed for clarity of

notation, let us denote ∆Ij

4

=I(Xj ; H

(N)

j

) − I(Xj ; H

(N−1)

j

). Then from (13) and the last expression of (10), we get

∆Ij =

1

2

log 

Dj (N − 1)

Dj (N)



. (14)

Alternatively, the innovations at the Nth stage, γN = XN − XˆN . Then following the standard derivation for the

Kalman filter [16], it can be shown that variance of the innovations

PγN = σ

2

V (N)



1 +

1/σ2

V (N)

1

σ2

x

+

PN−1

i=1

1

σ

2

V (i)



 , (15)

which shows that, for each feature point, the incremental mutual information is related to PγN as

∆I =

1

2

log 

PγN

σ

2

V (N)

!

. (16)

These relationships provide an alternative estimation theoretic interpretation to our result. Taken together (10), (14)

and (16) demonstrate the use of statistical evaluation techniques to the SfM problem, when it is suitably formulated.

3 Analysis and Experiments

3.1 Analysis:

Present methods to evaluate the quality of a reconstruction involve computing the distortion in (12). For a fusion

algorithm, this means that we need to compute (12) at every stage of the fusion and decide when to stop. This is

computationally intensive, distortion measures are not always very useful in practical experiments since the choice of

an acceptable threshold if often arbitrary and the source of the error (whether in the intermediate reconstructions or

in the fusion algorithm) is difficult to identify. In our approach, (10) gives a direct way to measure the contribution

of the intermediate solutions and the accuracy of the final solution as the algorithm progresses. The statistics of

the error can be computed using the SfM equations and its solutions, as described in [15]. If the solution is far

from its desired values, the error would be larger than if the solution is close to its true value. When the error in

the intermediate reconstructions is small, Dj is small and hence the difference in the mutual information is small.

Ideally, this difference should go to zero as we include more and more observations. If the error is large, Dj would

be large and ∆Ij would not decrease appreciably with the number of observations. Another salient feature of our

method is that we measure the information content between the true structure and the reconstructions before the

5
fusion. This allows us to understand the source of the error better since the effect of intermediate reconstructions

and fusion algorithm are separated.

One scenario where this idea can be applied is reconstruction from a video sequence where intermediate reconstructions, H(1), ..., H(L), obtained from a few frames (two or three) are combined together. Another application would be where partial reconstructions have been obtained from multiple cameras 3

. These partial models

would have common overlapping regions which can be combined together to form the single estimate. In this case,

H(1), ..., H(L) would represent these common sub-regions from L separate reconstructions.

The statistical assumptions of independence and Gaussianity are necessary in order to derive closed form expressions for the quantities of interest. The independence of the intermediate estimates H(1), ..., H(L) may be

valid when these are obtained from separate imaging systems and then combined. When the same camera is used,

the intermediate reconstructions should be obtained with non-overlapping frames; otherwise the common frames

increase the dependencies. Regarding the Gaussianity assumptions, it has been pointed out by Zhang in [7] that the

correspondence errors in SfM are usually normally distributed, if we can get rid of the outliers in the matches.

3.2 Experiments:

Experiment 1: A set of 3D points were generated so that we know their true positions. The perspective projections

of these points were generated and Gaussian noise with zero mean and known variance was added to these 2D

locations. The projections were taken for different positions of the camera, so that in the end a set of tracked features

was obtained. From every pair of such tracked features, the positions of the original 3D points were estimated,

which results in a set of 3D reconstructions. The first plot of Figure 2(a) shows the true value of the 3D points and

their estimated reconstruction from all the frames over which the features could be tracked. 4 The second diagram

in Figure 2(a) plots the decrease in the incremental mutual information with the increasing number of intermediate

reconstructions.

Experiment 2: As in the previous simulation, a set of features were tracked over a number of frames. However, the

level of noise added to the feature positions was higher and it led to a mismatch of some of the features. The 3D

positions of the points were estimated using the SfM algorithm and the results were erroneous as is clear from the

first plot of Figure 2(b). The second plot of Figure 2(b) depicts this case where the incremental mutual information

remains large and does not follow any trend.

Experiment 3: We will now present our result on a real video sequence. The video consists of a person moving his

head in front of a static camera. The aim was to reconstruct the model of the head of the person from this video.

The focal length of the camera was known. Figure (3)(a) represents an image from the video along with some of

the feature points which were tracked. Figure (3)(b) represents the change in the incremental mutual information

between the unknown 3D structure and the intermediate reconstructions from every pair of frames. Based on this

measure, the 3D model was reconstructed using 25 frames and Figure (3)(c) shows one particular view of this model.

4 A Discussion on the Usefulness of an Information Theoretic Criterion for

Vision Algorithms

The statistical quality analysis of computer vision algorithms has been studied quite extensively (see [14] for a

detailed literature survey on this topic). However, most of the methods have relied on computing the second order

statistical moments, like covariance of the estimate. The covariance is a preferred measure because of its relation to

the Cramer-Rao lower bound (CRLB), which dictates the minimum variance that an estimator can achieve [16]. If

the variance of a sequence of estimates (say, of the 3D structure) tends towards the CRLB, then the estimate is said

to be asymptotically efficient. However, computation of the CRLB often assumes that the estimate is unbiased (see

[6]). This is because, computing the bias of an estimator is not an easy task. Hence, even though expressions exist

3This is the set-up in the “Eye Vision” technology developed by Carnegie Mellon University (CMU) and CBS Television

(http://www.ri.cmu.edu/events/sb35/tksuperbowl.html).

4The first point was used to set the scale of the reconstruction, so that the geometric indeterminacies do not affect the result.

6
1 2 3 4 5 6 7 8 9 10

5

10

15

20

25

30

35

True and Estimated Depth Values

2 4 6 8 10 12 14

0

0.1

0.2

0.3

0.4

Plot of Incremental Mutual Information

1 2 3 4 5 6 7 8 9 10

−10

0

10

20

30

40

True and Estimated Depth Values

2 4 6 8 10 12 14

0

0.1

0.2

0.3

0.4

Plot of Incremental Mutual Information

(a) (b)

Figure 2: (a): The upper plot shows the true value of the depth of the 3D points using the solid line and the fused estimate from the intermediate

reconstructions from all the frames using the dotted lines. The second diagram plots the decrease in the incremental information with the

increasing number of frames. (b): The upper plot shows the true value of the depth of the 3D points using the solid line and the fused estimate

from the intermediate reconstructions from all the frames using the dotted lines. The lower plot is the change in the mutual information with

increasing number of frames. This is the case where the estimated reconstruction does not converge to the true value even with increasing

observations.

0 5 10 15 20 25 30

0

0.05

0.1

0.15

0.2

0.25

(a) (b) (c)

Figure 3: The above figures represent a 3D reconstruction from video using the method of measuring the IMI to judge the quality of the result.

(a) is one of the images from the video along with the set of tracked features used for the reconstruction. (b) represents the change in the IMI with

the number of images; (c) depicts one view from the reconstructed model.

for the CRLB of a biased estimator (known as the generalized CRLB), it is rarely used. The other main objection to

the use of variance as a measure of quality is that it neglects the effect of higher order statistics. This is often a major

approximation because the outliers, which are the source of many problems in computer vision algorithm, are often

not modeled accurately by second order statistics.

Recent work [17, 18] has shown that the motion and depth estimates are statistically biased, and the bias is

significant. This bias often propagates through later stages of the computation that rely on the motion and depth

estimates. Also, as we have shown in [15], the noise in the SfM estimates is significantly non-Gaussian. Hence we

propose that an information theoretic criterion which works by estimating the probability distribution function (pdf)

of the concerned physical quantities (e.g. the depth), rather than concentrate on certain moments only, is a more

suitable measure for a number of vision problems. The method of estimating the pdf will depend upon the particular

algorithm and underlying assumptions. The major limitation of an information theoretic criterion is its efficient,

robust and accurate estimation. This is because it is often difficult, and computationally expensive, to estimate the

probability density functions of the parameters of interest. However, estimation of MI has received some attention

7
among researchers in signal processing and information theory [19]. It is our hope that such information theoretic

criteria, as proposed in this paper, will become practically applicable as progress is made on robustly estimating

them.

5 Conclusion

In this paper, we have introduced a method to evaluate the quality of 3D reconstruction from a video sequence.

Existing methods rely on computing the distortion between the projections of the reconstructions and the original

images and deciding that the reconstruction is of acceptable quality when the distortion is below a certain empirically

chosen threshold. In this paper, we have shown that it is possible to evaluate the quality of the 3D structure estimate

as the algorithm proceeds by computing the incremental mutual information, which determines the importance of

considering an additional observation. It is related to the decrease in the coding length of the actual structure

conditioned on the increasing number of observations. Finally, experimental results have been provided to justify

these claims.

References

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8
Modular Programming Techniques for Distributed Computing 

Tasks 

Anthony Cowley, Hwa-Chow Hsu, Camillo J. Taylor 

GRASP Laboratory 

University of Pennsylvania, Philadelphia, PA, USA, 19104 

ABSTRACT 

This paper describes design patterns used in developing a software 

platform for mobile robot teams engaged in distributed sensing and 

exploration tasks. The goal of the system presented is to minimize 

redundancy throughout the development and execution pipelines by 

exploring the application of a strong type system to both the 

collaborative development process and runtime behaviors of mobile 

sensor platforms. The solution we have implemented addresses both 

sides of this equation simultaneously by providing a system for selfdescribing inputs and outputs that facilitates code reuse among 

human developers and autonomous agents. This well-defined 

modularity allows us to treat executable code libraries as atomic 

elements that can be automatically shared across the network. In this 

fashion, we improve the performance of our development team by 

addressing software framework usability and the performance and 

capabilities of sensor networks engaged in distributed data 

processing. This framework adds robust design templates and 

greater communication flexibility onto a component system similar 

to TinyOS and NesC while avoiding the development effort and 

overhead required to field a full-fledged web services or Jini-based 

infrastructure. The software platform described herein has been used 

to field collaborative teams of UGVs and UAVs in exploration and 

monitoring scenarios. 

KEYWORDS: sensor network, distributed computing, 

software design 

1. INTRODUCTION 

As efforts to field sensor networks, or teams of mobile 

robots, become more ambitious [5], [11], [4], 

communication constraints rapidly become the 

bottleneck both in the development effort and execution 

environment. From a development standpoint, human 

networking becomes clumsy as team sizes grow, putting 

team communications at a premium. Therefore, effort 

should be spent to optimize away the time developers 

must spend explaining things to each other, specifically, 

how to write code that has already been written or how 

to reuse existing code. If this aspect of collaborative 

development is not explicitly addressed, the team runs 

the risk of either losing the ability to reuse code, due to a 

lack of shared understanding, or drastically curtailing 

productivity by devoting excessive time to 

documentation efforts. Ideally, each developer’s efforts 

will be documented extensively enough for others to 

easily reuse the existing code without placing an 

undesirable documentation burden on the original 

developer. 

 The desire for software agents to autonomously 

exploit existing code is a subtly parallel goal. Should an 

agent be able to specify its requirements, it ought to be 

able to identify any existing code that would meet this 

need. This applies both in the sense of agents 

discovering new sources of data, and that of interactive 

data processing requests. We wish to field a sensor 

network wherein one sensor can tap into a potentially 

live data stream without any a priori knowledge of other 

nodes or their capabilities, while also giving each node 

on the network the ability to ask questions that require 

the processing of large amounts of data. In the first 

case, we need to give our agents the ability to identify 

the types of data being exported by other agents. This is 

addressed by having communication endpoints describe 

the data they trade in. The latter case involves not only 

finding the correct type of data, but also sending an 

active query to the data rather than saturating the 

network by bringing the data to the query. Such 

behavior requires descriptions of data sources and sinks, 

as well as the ability to move, command, and control 

executable code across the network. 

2. IMPLEMENTATION 

A crucial aspect in the development of this framework 

design philosophy is the relationship between the new 

software and that which it is built upon. We chose to 

develop our high level environment on top of an already 

full-featured platform. In our case, this platform was 

Microsoft’s .NET technology, which includes a strong 

type system in the .NET CLR (Common Language 

Runtime), an object-oriented language in the form of 
C#, and many varieties of network functionality in the 

.NET Class Library. Our design then focused both on 

what functionality we wished to add and that which we 

wished to remove. Simply put, we want to impose some 

structure on our developers that is not inherent to C#, 

.NET, or any existing platform. This structure is a 

fundamental part of the ROCI (Remote Objects Control 

Interface) [6], [9] philosophy, and is imposed on the 

ROCI developer as a form of design control that we 

believe adds a level of reliability to the resultant system. 

By imposing a prescribed design on developers, we are 

better able to isolate potential weaknesses and build in 

error detection and handling functionality. 

 

 ROCI itself is a high level operating system useful 

for programming and managing sensor networks. The 

core control element in the ROCI architecture is the 

ROCI kernel. A copy of the kernel runs on every entity 

that is part of the ROCI network (robots, remote 

sensors, etc.). The kernel is responsible for handling 

program allocation and injection. It allows applications 

to be specified and executed dynamically by forming 

communication connections and transferring code 

libraries to the nodes as needed. The kernel is also 

responsible for managing the network and maintaining 

an updated database of other nodes in the ROCI 

network. In this way, ROCI acts as a distributed peerto-peer system. Nodes can be dynamically added and 

removed from the network, and information about these 

nodes and the code running on them is automatically 

propagated throughout the system without the need for a 

central repository. 

 The control functionality needed by such a kernel is 

made possible by self-contained, reusable modules. 

Each module encapsulates a process which acts on data 

available on its inputs and presents its results on well 

defined outputs. Thus, complex tasks can be built by 

connecting inputs and outputs of specific modules. 

These connections are made through a pin architecture 

that provides a strongly typed, network transparent 

communication framework. A good analogy is to view 

each of these modules as an integrated circuit (IC) that 

has inputs and outputs and does some processing. 

Complex circuits can be built by wiring several ICs 

together, and individual ICs can be reused in different 

circuits. ROCI modules have been developed for a wide 

range of tasks such as: interfacing to low level devices 

like GPS units and cameras, computing position 

estimates based on GPS, IMU and odometry data, 

acquiring stereo panoramas, platform motion control, 

online map building and GPS waypoint navigation. 

 ROCI modules are further organized into tasks 

(Figure 1). A ROCI task is a way of describing an 

instance of a collection of ROCI modules to be run on a 

single node, and how they interact at runtime. Tasks 

represent a family of modules that work together to 

accomplish some end goal – a chain of building blocks 

that transforms input data through intermediate forms 

and into a useful output. A task can be defined in an 

XML file which specifies the modules that are needed to 

achieve the goal, any necessary module-specific 

parameters, and the connectivity between these 

modules. Tasks can also be defined and changed 

dynamically by starting new modules and connecting 

them with the inputs and outputs of other modules. 

Figure 1. A typical ROCI task: a collection of behavior 

modules with loggers connected to specific pin 

connections. A human operator interfaces with the logs 

via the browser, which may be running on a different 

machine from the task.

 The wiring that connects ROCI modules is the pin 

communication architecture. Pin communications in 

ROCI are designed to be network transparent yet high 

performance. Basically, a pin provides the developer 

with an abstract communications endpoint. These 

endpoints can either represent a data producer or a data 

consumer. Pins in the system are nothing more than 

strongly typed fields of the module class, and so are 

added to modules with a standard variable declaration 

statement. Pin communication allows modules to 

communicate with each other within a task, within a 

node or over a network seamlessly. The base Pin type 

will optimize the connection based on whether or not it 

is local and handle all error detection and handling, 

bandwidth utilization requirements, and optional 

buffering. The type system enforces pin compatibility at 
run time which makes it impossible to connect inputs 

and outputs of incompatible types. 

 This compatibility evaluation is done in an objectoriented fashion such that, when necessary, output data 

will be transparently up-cast before being transmitted to 

a data sink. This negotiated compatibility allows for 

what we call “blind polymorphism,” which does not 

require that both nodes have all the same types loaded. 

That is to say, if data can be cast up its inheritance 

hierarchy to the type that the data sink requires, then this 

cast will be done on the source side of the connection, 

thereby not requiring that the sink be aware of the 

inherited type. 

 Importantly, the modules in the system are self 

describing so that the kernel can automatically discover 

their input and output pins along with any user-settable 

parameters. These features of the ROCI architecture 

facilitate automatic service discovery since a module 

running on one ROCI node can query the kernel 

database to find out about services offered by modules 

on other nodes and can connect to these services 

dynamically. 

The self describing behavior of module inputs, 

outputs, and parameters is achieved automatically 

through the use of the underlying type system. This is 

an important element of ROCI’s ability to limit the 

potential for developer error. In the process of 

identifying necessary input and output pins, the module 

developer naturally defines certain data structures that 

the module takes as input and generates as output. 

These data structures represent a form of design contract 

that tells other users what type of input the module can 

parse, and what type of output it generates. This 

information is what the pin type system is built upon: a 

particular type of pin is designed to transfer a particular 

type of data. These types can then be used to verify 

potential connections between pins. By relying on type 

information that the developer necessarily creates by 

designing module-appropriate data structures, we are 

able to obviate the need for any separate developergenerated description of a module’s inputs and outputs. 

Such descriptions run the risk of becoming out of date, 

and are not always easily checked. Relying on the type 

system, however, means that if a module incorrectly 

parses an input data structure, for example, it will not 

compile. In this way we guarantee that if a Module 

compiles, then it must be compatible with the associated 

data description. 

2.1. The Task Programming Model

The abstraction gained by treating modules as primitive 

components allows us to bring compiler-level features to 

bear on ROCI tasks. Specifically, the idea of type 

checking the input/output connections between modules 

has already been covered, but type checking the 

parameters that govern the behavior of these modules is 

also provided at the task level. 

Individual module authors are able to decorate 

class-scope variable declaration statements with 

attributes that specify whether or not a variable is a 

startup parameter, or even if it is a control parameter 

that should be modifiable at run time. These attributes 

are extracted from compiled code, and are used by the 

ROCI to kernel to expose these variables when 

appropriate. 

Variables marked as startup parameters will be 

displayed in the browser UI when a user wishes to start 

a task. Type checking is performed as the user enters 

new values for these parameters, thus making it far less 

likely that a module will start with invalid parameters. 

Furthermore, the type of the parameter can be used to 

intelligently populate the parameter-setting UI by 

dynamically creating UI elements such as drop-down 

boxes with only valid values as options, as opposed to a 

text field for every parameter. Variables marked as 

control parameters (dynamic over the course of 

execution) can be modified by another standard browser 

interface. A running module can be selected, and any 

variables marked as control parameters will populate a 

parameter-setting UI similar to the one described for 

startup parameters. This functionality, built atop the 

strong type system in .NET, provides a compiler-like 

layer of type checking at all phases of execution, while 

simultaneously making the UI used to interact with a 

ROCI deployment more intuitive for the end user.

2.2. General Instrumentation 

The notion of task as program allows for varied 

interesting forms of system-level instrumentation and 

control. First, by sufficiently isolating individual 

modules such that they can be treated as atomic 

operations, we are able to treat tasks as programs built 

on a language that uses the specified modules as 

statements. Second, by virtue of its role as provider of 
all inter-module communications, the ROCI kernel is 

capable of rich monitoring and control of all data 

transactions. These two points both deal with the notion 

of program flow control. 

 Program flow control is primarily controlled by the 

sequence of operations specified in the program. In our 

case, a schedule of modules makes up the procedural 

part of a task program. As described above, a task is a 

collection of concurrently running modules. The order 

in which these modules run is not explicitly defined, but 

instead is effectively governed by data dependencies 

between modules. In general, if module alpha uses data 

from module beta, then module alpha will block until 

that data is available, thus creating a very loose schedule 

in which each iteration of module alpha’s processing 

loop is preceded by at least one iteration of module beta. 

There are no guarantees on the efficiency of this 

schedule; if only module alpha uses module beta’s 

output, then it may be wasteful for module beta to run at 

a higher rate than alpha. 

 This issue is addressed by having a task schedule. 

The task schedule merely specifies a linear sequence of 

module iterations, but can be leveraged to obtain far 

greater efficiency that a schedule governed solely by 

dependency blocking. This schedule is specified in the 

task XML file as a sequence of module names. The 

names are checked when the task file is loaded to ensure 

that all statements in the schedule are defined module 

names. This schedule can be used simply to eliminate 

wasted iterations of data producers, but it can also be 

used to obtain non-obvious gains in overall program 

efficiency. A schedule can include a bias to run a 

particular module more frequently than another if it 

would give the task, taken as a whole, greater efficiency. 

Furthermore, since this schedule is not encoded in 

compiled code, it is fully dynamic. That is, a user or 

automated process can adjust a task’s schedule at 

runtime to meet changing resource availability or 

execution priorities. 

 Such behavior is dependent on information. This 

information is made available by the instrumentation 

built into task schedules. The mechanisms that govern 

the execution of a ROCI task are in good position to 

monitor the iteration frequency of the task schedule in 

its entirety, and the resources being used by individual 

modules. This information can be used to raise alarms 

when a task frequency drops below a specified 

threshold, to throttle iteration frequency, or to modify 

the schedule to make better use of available resources. 

Furthermore, application specific efficacy metrics can 

be utilized by task monitoring modules to initiate new 

schedules to improve efficiency. 

 The distributed nature of ROCI deployments 

suggests a form of program flow throttling apart from 

the usual method of CPU resource allocation: network 

resource allocation. While the scheduling system can be 

used to monitor and control the rate at which a task 

schedule iterates, ROCI’s pin system can throttle 

network communications on a connection-byconnection basis. Individual pin connections can be 

monitored to examine the type of data being transmitted, 

the frequency of transmissions, and the bandwidth used. 

Both the frequency of transmission and the overall 

bandwidth used are controllable by the ROCI kernel. 

This allows a controller, human or automated, to give 

network precedence to certain connections, potentially 

allowing greater system effectiveness with limited 

resources. Note that by throttling network 

communications, the speed at which a networked task 

runs can be controlled. Especially in a schedule-free 

execution environment, wherein a collection of modules 

have their iteration frequencies mediated by data 

dependencies, the throttling of individual connection 

bandwidth can be used to control the iteration frequency 

of individual modules. Thus there are two distinct 

methods of controlling performance in an on-demand 

fashion based on mediating CPU or network resource 

allocation. 

2.3. Logger Modules 

Our sensor database [12], [10] system is implemented 

on top of ROCI through the addition of logger modules. 

These logger modules can be attached to any output pin 

and record the outputs of that pin’s owner module in a 

time-stamped log which can be accessed by external 

processes. These logger modules appear to the system as 

regular ROCI modules which means that they can be 

started and stopped dynamically and can be discovered 

by other ROCI nodes on the system. This last point is 

particularly salient since it means that robots can learn 

about the records available in other parts of the network 

at run time as those resources become available. Since 

logger modules can be attached to any output pin, there 

is no meaningful distinction between “low level” sensor 

data such as images returned by a camera module and 

“high level” information such as the output of a position 
estimation module. Any data that is relevant to a task 

can easily be logged through the addition of a logger 

module. 

Figure 2. Time is a useful index for synchronizing data 

concurrently collected from multiple sources. 

The generic logger module logs all incoming data 

based on time, an index relevant and meaningful 

regardless of the data type (Figure 2). Additional 

indexing methods that are specific to a particular data 

type are easily implemented by creating a new type of 

logger module that inherits from the general logger and 

is explicitly usable only with the expected data type. 

For example, a logger module that records the output of 

a GPS unit may also support efficient indexing based on 

position. Using time as a common key provides a 

simple mechanism for correlating information from 

different channels. Consider, for example, the problem 

of obtaining all of the images that a robot acquired from 

a particular position. This can be implemented 

efficiently by first indexing into the GPS log to find the 

times at which the robot was at that location and then 

using those times to index the image log to pull out the 

images taken from that vantage point. Using time as a 

common index also eliminates the need for a fixed 

database schema on the robots: different logger modules 

can be added or removed from a node as needed without 

having to perform complex surgery on a global table of 

sensor readings. Since the logger processes do not 

interact directly, they can be started and stopped, added 

and removed independently of each other. 

2.4. Query Processing 

Once a relevant data log has been found on the network, 

one must then face the problem of executing a query to 

extract information from that archive. It is often the 

case that the volume of data stored in a log makes it 

unattractive to transfer the data over the network for 

processing. In these situations we can take advantage of 

the fact that the facilities provided by ROCI can be used 

to support distributed query processing. Consider the 

example of a UAV that stores a log of images acquired 

as it flies over a site. If a process on a UGV wanted to 

access this data to search for particular targets in the 

scene, it would be impractical to transfer every image 

frame to the ground unit for processing. Here it makes 

sense to consider sending an active query to the UAV 

requesting it to process the images and send the target 

locations back to the UGV. This can be accomplished 

by developing a ROCI module that extracts the targets 

of interest from UAV imagery and then sending this 

module to the UAV as part of a query. The ROCI kernel 

on the UAV would then instantiate a task and use this 

module to process the data in the image log returning 

the results to the UGV. 

Sophisticated queries that involve chaining together 

the results of many processing operations or combining 

information from several logs can be handled through 

precisely the same mechanism. The query takes the 

form of a network of ROCI modules that carry out 

various phases of the query. The modules in this task 

are distributed to appropriate nodes on the network and 

the final output is returned to the node that initiated the 

request. This approach allows us to dynamically 

distribute the computation throughout the network in 

order to make more efficient use of the limited 

communication bandwidth. 

Another feature of this approach is that it promotes 

code re-use since the modules that are developed for 

carrying out various data processing and analysis 

operations online can also be used to implement queries 

on stored data logs (Figure 3). This is important not just 

by virtue of facilitating rapid development, but also by 

the robustness and familiarity users have with the 

component modules used in all aspects of a ROCI 

deployment. By making the same framework pervasive 

throughout the development pipeline, users are able to 

concentrate their efforts on improving core techniques 

because the code only needs to be written once. Once 

the code has been written, users setting up robot 

behaviors work from the same toolbox as those 

formulating queries at run time and throughout postprocessing. 
Figure 3. A ROCI query is, in many ways, very similar 

to a real-time task. In many cases, the inputs of the task 

come from live sensors, while the query gets data from 

logs. This distinction is transparent to the component 

modules. 

The notion of query stages combined with the strong 

type system underlying ROCI module inputs and 

outputs immediately opens the door for a multitude of 

queries that make use of functionality already used by 

robot behaviors. For example, a robust localization 

routine may be run on all robots as they move around 

the environment. This routine must update relatively 

quickly to allow the robot to navigate in real-time, thus 

necessitating that it only consider readily available data. 

However, a user or autonomous agent may require an 

alternate estimation of a robot's location at a particular 

time in the past, perhaps utilizing newly acquired data. 

This can be achieved by designing a query wherein a 

localization routine, possibly another instance of the 

original routine, is connected to not only locally 

collected data, but also to any number of data processing 

routines, also specified by the query body, running on 

any number of other nodes. This localization may take a 

relatively long time to execute, and may not be suitable 

for real time control, but it is available to any 

programmed behavior or human operator that requests 

it. This query, while complex, automatically benefits 

from the shared toolbox provided by the consistent 

design framework. Processing modules that already 

exist on data hosts need not be transmitted, while others 

are downloaded from peers on an as-needed basis. The 

query itself is analogous to a behavior task: it specifies 

processing modules and how they connect. The ROCI 

kernel handles the work of ensuring that modules exist 

on the nodes that need them, and that those modules are 

properly connected. 

By applying distributed database methods and 

techniques, the architecture presented here frees 

designers from having to create a static, allencompassing communications scheme capable of 

satisfying a set of pre-specified query types. Instead, 

individual developers are able to utilize all sensor 

network resources in a modular, dynamic fashion 

through the use of active distributed database queries. 

3. APPLICATIONS 

ROCI technology is being used throughout the GRASP 

Lab to power a variety of robotics projects. The 

structure supported by ROCI facilitates the design of 

complex single-platform systems, high-performance 

real-time behaviors, and relatively simple static sensors. 

Projects such as the Smart Wheelchair utilize ROCI to 

organize and make sense of the data collected by dozens 

of sensors on a single mobile platform. Teams of small 

truck-like robots (Clodbusters) use ROCI for everything 

from collaborative error minimization to vision-based 

obstacle avoidance. Even a fixed camera becomes far 

more useful when plugged into a computer running 

ROCI. ROCI immediately provides logging capabilities 

as well as the ability to expose the camera’s data stream 

to the network. Teams of ROCI-powered vehicles made 

up of Clodbusters, fixed wing UAVs, and an 

autonomous blimp have been successfully fielded in 

exploration and navigation experiments under adverse 

network conditions as part of the DARPA-funded 

MARS2020 program. 

Current database-related work involves visualization 

and exploitation of data generated by a heterogeneous 

team of ground and air robots equipped with cameras, 

GPS receivers, IMU readers, altimeters and other 

sensors. For visualization purposes, this data can be 

fused in an on-demand fashion through visualization 

modules a human operator can interact with. In this 

way, one can quickly bring up images taken by a UAV 

flying over a particular location by joining a GPS log 

with an image log over a time index. Of note is what 

data is sent over the network to meet a particular 

demand. To minimize network usage, one might use a 

map location selected by the user to index into a GPS 

log to see when the robot was at the desired location, if 

it ever was. The resultant time indices can be used to 

index into the image database, thus avoiding the need to 

transfer unnecessary images. 

An alternate formulation of this scenario that still 

maintains network efficiency, while improving usability, 

is to obtain the time indices of all images taken within 

some timeframe. These indices can be used to index 

into the GPS log to present the user with a map marked 
up with the locations where pictures were taken. The 

user can select one of these locations, thus providing the 

database system with a time index to use in obtaining a 

particular image. This solution exploits the fact that 

both time indices and GPS data are far more compact 

than image data. The goal is to transmit as narrow a 

subset of the largest data log, in this case the image log, 

as possible. This setup is what is used at the GRASP 

Lab to intuitively scan data collected during a team 

operation. 

A behavior-oriented application of the logging 

functionality can be found in a mobile target acquisition 

behavior. In this scenario, periodically placed overhead 

camera nodes log their image data which is made 

accessible to mobile robots when a network route to the 

camera node exists. Given a piece of code for visually 

identifying a target, a mobile robot can move to within 

routed radio range of overhead camera nodes and inject 

the target identification code as part of an image log 

query. The results of this query can simply be the time 

indices when the target was visible to the overhead 

camera. This information can be used to improve the 

efficacy of visual target searches – an extremely dataintensive process -- while minimizing the burden placed 

on the network. Under lab conditions, a two-node 

network, using a technology based on 802.11b ad-hoc 

networks, may be expected to manage 300KB/sec data 

transfer rates. This would mean that a single, 

uncompressed 1024x768 color image (2.25MB) would 

take over 7 seconds to transfer. While compression can 

greatly help, any resultant artifacts could cripple the 

effectiveness of a given processing algorithm. 

Regardless, a factor of 10 gained in compression is more 

than lost when faced with an image log of thousands of 

images. Compare this to the 20-50KB size of a typical 

ROCI module DLL, and it is clear that transferring the 

code rather than the data often presents considerable 

advantages. 

4. EVALUATION

The primary benefit of ROCI is the development 

process it suggests. Developing high level applications 

from reusable, modular components is a wellunderstood concept, but one whose acceptance has faced 

real difficulties as popular programming technologies 

have not kept up with the requirements of modern 

design techniques. ROCI represents an attempt to push 

the field forward by taking full advantage of powerful 

hardware as well as relatively modern programming 

techniques such as object-oriented programming and 

strong type systems. By building consistent support for 

the type system into our high level framework we have 

successfully allowed loosely structured development 

teams to collaborate on large-scale projects with more 

reliable results than is usual. The task-module-pin 

design structure encourages engineers without strong 

computer science backgrounds to contribute to larger 

projects without having to worry about their lack of 

understanding of the underlying system. Most 

developers concentrate on the specifics of what their 

module does, not how it fits into a larger system, or how 

any of the internal mechanisms – such as scheduling, 

communications, or user interface – work. 

4.1 Related Work 

 Similar systems exist for other application 

scenarios. TinyOS is an open-source effort to provide 

OS-level support for sensor platforms with extremely 

limited hardware. In fact, the fundamental design 

concepts of TinyOS and ROCI have much in common, 

primarily the encouraging of modular software design 

[1]. However, TinyOS specifically targets limited 

hardware platforms, which imposes limits on what can 

be attempted with it. We have chosen to target much 

more capable hardware – we use consumer-level laptop 

computers on many of our robots – and we are therefore 

able to distance ourselves from many of the difficulties 

faced by the mote programmer. 

 Distributed computing infrastructures that target 

more powerful hardware can also be found. Several 

Grid computing efforts are making large strides towards 

harnessing the computational power of thousands of 

computers over the Internet [3]. These efforts tend to be 

of a much more general slant than what we have 

undertaken. We have found that by focusing on the 

needs of our developers, we are better able to define 

constraints on the development process that significantly 

improve reliability. While the event-based pin 

communications infrastructure ROCI employs works 

well for sensor platforms exchanging data, it is not 

necessarily optimal for all computing needs. Further, 

we do not provide any tools for automating the 

distribution of a single computation over a very large 

network. 
 Sun’s Jini system for Java is an architecture that 

attempts to bridge the gap between embedded systems 

and services running on general purpose computers [2]. 

While this system boasts many of the same benefits as 

ROCI, we feel that it requires somewhat more effort on 

the part of the developer to make use of. The simplest 

ROCI deployments involve minimal usage of ROCI API 

calls. There is a template module that an author fills 

out, and then each pin connection in a task is specified 

in one line of XML. This type of deployment is an 

example of how the ROCI kernel is designed to handle 

most common usage patterns with minimal developer 

action. 

4.2 Final Words

 The ROCI system is evidence that a strong type 

system paired with solid software design fundamentals 

can yield substantial improvements in software 

reliability, reuse, and ease of use. While still primarily 

used in robotics efforts, projects that seek to stretch 

ROCI design methods in new directions, such as limited 

hardware devices and schedule optimization, are now 

underway. By defining the ROCI kernel itself in a 

modular fashion with well-defined interfaces, we are 

able to extend the offered functionality, usually without 

breaking backwards compatibility. This extensibility, 

both in terms of novel task-level applications and kernel 

extensions, is a validation of the design methods 

presented above. 

5. REFERENCES 

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B. Southall, J. Spletzer, and C. Taylor, “A framework 

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[12] Samuel R. Madden, Michael J. Franklin, Joseph 

Hellerstein, and Wei Hong, “The design of an 

acquisitional query processor for sensor networks,” In 

SIGMOD, June 2003. 

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13(1/2): pp. 91-128, 1999. 
Evaluating Reliability of Motion Features in Surveillance Videos 

Longin Jan Latecki1, Roland Miezianko1, Dragoljub Pokrajac2 1

Temple University, CIS Dept., Philadelphia, PA, latecki@temple.edu, rmiezian@temple.edu 

2

Delaware State University, CIS Dept., Dover, DE, dpokraja@desu.edu 

ABSTRACT 

Although a tremendous effort has been made to perform a 

reliable analysis of images and videos in the past fifty years, 

the reality is that one cannot rely 100% on the analysis results. 

The only exception is applications in controlled environments 

as dealt in machine vision, where closed world assumptions 

apply. However, in general, one has to deal with an open 

world, which means that content of images may significantly 

change, and it seems impossible to predict all possible 

changes. For example, in the context of surveillance videos, 

the light conditions may suddenly fluctuate in parts of images 

only, video compression or transmission artifacts may occur, a 

wind may cause a stationary camera to tremble, and so on. 

The problem is that video analysis has to be performed in 

order to detect content changes, but such analysis may be 

unreliable due to the changes, and thus fail to detect the 

changes and lead to “vicious cycle”. 

The solution pursuit in this paper is to monitor the 

reliability of the computed features by analyzing their general 

properties. We consider statistical properties of feature value 

distributions as well as temporal properties. Our main strategy 

is to estimate the feature properties when the features are 

reliable computed, so that any set of features that does not 

have these properties is detected as being unreliable. This way 

we do not perform any direct content analysis, but instead 

perform analysis of feature properties related to their 

reliability. 

The main effort in video analysis nowadays is still in 

making the feature computation more reliable. Our claim is 

that we need to accept the fact that the computed features will 

never be 100% reliable, and focus our attention on computing 

reliability measures. This way system decisions will only be 

made when features are sufficiently reliable. This means for 

an intelligent system for video analysis that in addition to 

feature computation, it should perform instantaneous 

evaluation of their reliability, and adapt its behavior in 

accordance to the reliability. For example, if the goal of a 

system is to monitor motion activity, and to signal an alarm if 

the activity is high, the system is allowed to make reliable 

decisions only if there exist a subset of the computed motion 

activity features that is sufficiently reliable. The monitoring of 

features reliability and adjusting the system behavior 

accordingly, seems to be the only way to deploy autonomous 

video surveillance systems. 

1. INTRODUCTION 

We begin by showing two examples of video content 

changes that cause the existing motion detection approaches to 

inaccurately detect the presence of substantial motion. Clearly, 

the detected motion is present in videos, but it is due to some 

content artifacts and is not due to the actual presence of 

moving objects. Consequently, human observant ignores such 

“motion” as irrelevant, while standard video analysis systems 

detect it as significant activity. We will show that the feature 

reliability methods proposed in this paper allow us to identify 

the unreliable motion features, and to ignore the irrelevant 

artifacts. This is possible without reducing the detection rate 

of real moving objects. Consequently, we eliminate false 

alarms without reducing the detection rate. We stress that this 

is obtained without any direct video content analysis (e.g., 

using different features), but by monitoring the reliability of 

computed features. As stated in the introduction, direct video 

content analysis with further features does not solve the 

problem, since these features may also become unreliable. 

Our first example illustrates motion artifacts in Campus 31

video introduced by some reflections in windows that are 

probably caused by cars passing by. In Fig. 1, we show two 

frames from Campus 3 video, one showing real motion, and 

the second showing the motion artifacts in addition to the 

normal motion. Our second example, in Fig. 2(a), shows 

motion artifacts introduced by video compression. The same 

scene without such artifacts is shown in Fig. 2(b). This video, 

which we call Temple 2, was recorded in real-world 

environment by the video surveillance system of the Campus 

Police Division of the Temple University. 

In Section 2, we first describe a simple temporal method to 

determine the reliability of motion detection. In Section 3, we 

present a more sophisticated statistical method based on 

distribution analysis of feature values and information theory 

[21]. Both methods monitor features computed by our motion 

detection approach presented in [17], which we summarize in 

Section 4. The motion features are computed for gray level or 

infrared videos using 3D spatiotemporal blocks of spatial size 

8x8 pixels, and temporal size of 3 frames. The blocks are 

disjoint in space and overlap by one frame in time. As result 

we obtain motion activity values for each 8x8 block in every 

video frame. By thresholding the motion activity values, we 

 

1 Campus 3 can be obtained from the Performance Evaluation 

of Tracking and Surveillance (PETS) repository: 

ftp://pets.rdg.ac.uk/PETS2002//DATASET1/TESTING/CAMERA3_JPEGS/
obtain a binary feature, called motion detection, with 1 

standing for ‘motion detected’ and 0 for ‘no motion detected’. 

Both videos as well as our motion detection results can be 

viewed on [12]. 

(a) 

(b) 

Figure 1. Two frames from Campus 3 video with moving 

blocks highlighted red: (a) motion artifacts due to reflections 

in the windows, (b) the same scene (a few frames later) 

without the artifacts.

(a) 

(b) 

Figure 2. Two frames from Temple 2 video with moving 

blocks highlighted red: (a) motion artifacts introduced by 

video compression, (b) the same scene (a few frames later) 

without the artifacts. 

A temporal reliability analysis introduced in Section 2 is 

applied to the motion detection feature, while a statistical 

reliability analysis introduced in Section 3 is applied to the 

motion activity feature. 

2. TEMPORAL ANALYSIS OF FEATURE 

RELIABILITY 

In this section, we describe a simple temporal method to 

determine the reliability of motion features. The input motion 

feature has binary values for each 8x8 block for each video 

frame with 1 for ‘motion detected’ and 0 for ‘no motion 

detected’. The algorithm described in Section 4.2 computes 

this feature vector. The 8x8 blocks are disjoint. Let f(n) be the 

number of 1s in the frame number n, i.e., f(n) is the number of 

detected moving blocks as function of frame number. We use 

the finite difference approximation of first derivative of f to 

monitor the reliability of our motion detection. In simple 

words, if the jump in values of f is above a certain threshold 

for a given time interval, the binary feature is unreliable in this 

interval. The threshold necessary to detect the unreliable 

features is not static. We propose a dynamic thresholding 

algorithm described in Section 2.1 to learn and vary this 

threshold. However, some other learning techniques could 

also be used. 

This reliability property works under the assumption that 

there exists an upper bound on the size of moving objects 

whose motion we want to detect (measured in the number of 

moving blocks). This assumption holds for most surveillance 

videos. Now we consider an example video, called Temple 2,

that satisfies this assumption. This video is recorded by a roof 

mounted, stationary camera, so that a certain minimal distance 

to moving objects is guaranteed. Typical moving objects there, 

humans and vehicles, cannot get arbitrarily large. Hence, the 

fraction of the scene occupied by a moving object is limited. 

Observe that the actual value of the upper bound on the size of 

moving objects needs not to be known, since our algorithm 

learns it automatically. 

In Fig. 3(a), we see the graph of function f for Temple 2

video. Time intervals with significant jumps of f that are 

correctly identified by our dynamic thresholding are marked 

with red lines in Fig. 3(b). The graph of modified feature f, 

when f was set to zero within the time intervals when motion 

detection was detected as unreliable is shown in Fig. 3(c). Fig. 

3(c) shows that the proposed method is able to identify and 

exclude the unreliable results of motion detection. By 

excluding these time intervals from further processing, we not 

only eliminate false alarms, but make possible to correctly 

detect alarm situations, although the input motion detection in 

not 100% reliable. For example, a significant increase in the 

number of motion blocks after the frame 1700 indicates an 

alarm situation. This is a correct prediction, since a street fight 

is recorded on the video after the frame 1700, see the Temple 

2 video [12]. 
(a)

0 200 400 600 800 1000 1200 1400 1600 1800 2000 0

50

100

150

200

250

300

350

400

Temple2-Motion Measure per Frame

Frames

(b)

0 200 400 600 800 1000 1200 1400 1600 1800 2000 0

50

100

150

200

250

300

350

400

Temple2-Motion Measure and Noisy Frames

Frames

(c)

0 200 400 600 800 1000 1200 1400 1600 1800 2000 0

50

100

150

200

250

300

350

400

Temple2-Filtered Motion Measure per Frame

Frames

Figure 3. (a) The graph of f(n), which is the number of 

moving blocks as function of frame number n. (b) Significant 

jumps of f (caused by feature unreliability) correctly identified 

by our dynamic thresholding. (c) The graph of f padded by 

zeros for frames with unreliable motion detection.

2.1. DYNAMIC THRESHOLDING ALGORITHM 

Now we describe a dynamic thresholding algorithm used to 

detect the jumps of function f. First we compute the initial 

values of mean meanl and standard deviation stdl using all 

previous values of f(x) for x=1, ..., t-1 and some time instance 

t. The actual dynamic thresholding starts at time x=t. A jump 

up is detected at points x ∈{x +1, x + 2,.., x + w} for a 

window size w if 

meanrw(x) – meanl(x) > C1*stdl(x), 

where C1 is a constant. A dynamic threshold values meanl and 

stdl are updated if 

 meanrw(x) – meanl(x) < C2*stdl(x), 

where C2 < C1 is a second constant. The updated values are: 

meanl(x) = u*meanl(x) + (1-u)*meanrw(x)

stdl(x) = u*stdl(x) + (1-u)*stdrw(x)

where u is a learning constant and 

∑ ( ) =

= +

w

f x

w

meanrw x 1

1 ( ) τ

τ

∑( ) =

+ − − =

w

d x meanrw x

w

stdrw x 1

2 ( ) ( ) 1

1 ( ) τ

τ . 

The symmetric window constant w was set to 3, giving us 

a sliding window of 7 frames (2*w+1). The learning constant 

was u=0.9. Constants C1, C2 of function f used in detecting 

jumps of the Temple 2 video were selected based on the initial 

running average meanl and stdl. The value of meanl was 10.3 

and the value of stdl was 7.4. Constant C1 was set to 15 and 

constant C2 was set to 3 providing the initial jump detected 

threshold to 154.5 and reset to no-jump detected threshold of 

30.9. 

3. STATISTICAL ANALYSIS OF FEATURE 

RELIABILITY 

To determine whether a particular feature is reliable, we 

assume that the feature bears more information if its 

distribution differs more significantly from a normal 

(Gaussian) distribution. Similar heuristics are used e.g., in 

Independent Components Analysis [20]. The follow-up 

assumption is that the feature becomes unreliable if an 

addition random noise is superimposed, which would lead the 

distribution of such noisy feature to become more Gaussian 

like. Hence, by measuring to what extent a feature distribution 

differs from a Gaussian distribution, one can not only get 

information to what extent the feature is useful but also when 

such usefulness drops (e.g., due to some external and often 

non-observed factor). 

The Information Theory proposes negentropy as the 

measure of this discrepancy. Given a probability density p(x) 

of a feature, Differential Entropy is defined [18, 19] as: 

H() () () x = ∫ − p x p x dx ∞

−∞

log (1) 

For a given class of distributions p(x) that have the same 

variance 2 σ , differential entropy is maximal for a Gaussian 

distribution where it is equal 

( ) 2 2 log2

2

1 HGauss σ = π eσ . (2) 

Hence, a negentropy, which defined as 

( ) ( ) ( ) 2 J x H H x = Gauss σ − (3) 

or its normalized value 
( ) ( ) ( ) 2

2 ( ) / 1 σ σ

Gauss

Gauss H

H x J x H = − (4) 

may be used to measure usefulness and reliability of a feature. 

Observe that the minimal value of negentropy is 0 (when p(x) 

is Gaussian). 

A naïve approach to compute negentropy would be to 

employ histograms to approximate p(x) with piecewise linear 

function p’(x) such that: 

p (x) Kp(x ) x [ ] x x x ' = i , ∈ i , i + ∆ 

where K is a normalization constant (chosen such that p’(x) is 

a distribution). However, as shown in [21] this non-parametric 

technique is very unstable since dependent on a proper choice 

of a histogram bin size ∆x and histogram centers xi. Hence we 

use parametric approach suggested in Hyvarinen’s NIPS 1997 

paper [18]. The main ideas of this approach are: 

1) Instead of original feature x, use a standardized feature 

x*=(x-mean(x))/std(x) that have zero mean and unit standard 

deviation. This way, we could directly use negentropy to 

compare reliability with no need to normalize with the entropy 

of a Gaussian. 

2) Use a first-order Taylor approximation of a logarithmic 

function in eq. (1) that leads to: ( )( ) 1 log 1 / 2 2 + ε + ε ≈ ε + ε ; 

3) Use conveniently chosen set of orthogonal functions of 

Gi(x) of a feature x to expand probability density function p(x) 

in vicinity of a Gaussian probability density. 

In practice, the choice of orthogonal functions is based on 

practicability and sensitivity on outliers of the computation of 

estimates for expectations E(Gi(x)), integrability of the 

obtained probability density function approximation and last, 

but not the least, the properties of non-Gaussian distributions 

we want to capture. 

Based on such consideration, [18] proposes the following 

two approximations of negentropy, that we use in this paper: 

( ) ( ) ( ) 2

*

2

2 * / 2

1

* *2 2















 = ⋅ + − −

π J x k E x e k E x a

x

a

 (5a) 

( ) ( ) ( ) 2

/ 2

2

2 * / 2

1

*

2

*2 *2 1















 = ⋅ + − − −x

b

x

b J x k E x e k E e (5b) 

where the coefficients are determined as: 

16 3 27

24 , 6 2

24 , 8 3 936 1 2 2

− =

−

= − = a b k k k

π

. (6) 

The proposed technique is applicable on any continuous 

feature. In this paper, we evaluate the reliability of the motion 

activity feature, defined in [17] (see Section 4) as the largest 

eigenvalue of texture vectors in a small time window. For 

each frame, we standardize the feature values x*, compute 

expectations ( ) * E x , ( )2 * / 2 2 * x E x e − ⋅ and finally compute the 

negentropy approximations eq. (5a), (5b) per frame.

We evaluated the proposed techniques for assessing 

feature reliability on a set of videos [12]. This set includes 

infrared videos, for which the same settings of parameters as 

for visual light videos were used. Here we focus on our results 

on two video sequences from the Performance Evaluation of 

Tracking and Surveillance (PETS) repository: a sequence 

from PETS20012

 here referred to as Campus 1 sequence, a 

sequence from PETS2002, here referred to as the Campus 3

sequence and on a Temple 2 sequence from Temple 

University. 

Campus 1. At the beginning of the sequence, there is no 

movement, so changes in the motion activity (an observed 

feature) are random, which reflects small negentropy values in 

approximately first 100 frames, see Fig 4(a). Both negentropy 

approximations (eq. 5a, 5b) demonstrate strong drop between 

frames 1960 and 2000 which corresponds to the higher level 

of noise that can be visually observed between these frames. 

Function B (eq. 5b) provides more stable approximation 

values, which makes it potentially more useful. 

Campus 3. Both methods identified drop around frames 

330, 660, a strong drop around 700, a drop around 720 and the 

relatively long-term drop between 800 and 900, see Fig. 4(b). 

Finally, there were some small oscillations between 1200 and 

1300 and one drop around 1400. All these events correspond 

to frames in the video sequence when our algorithm has 

difficulties in properly identifying moving objects based on 

observed feature (e.g., due to reflections in the upper right part 

of the frame, cp. Fig. 1). Again Function B (eq. 5b) performed 

better, by having less oscillations and fluctuations. 

Temple 2. On this video, there is evident instability 

(manifested as flicker) that can be traced to applied 

compression technique. The period of this disturbance, which 

has negative effects on motion detection, is around 62 frames. 

Using the proposed technique, we obtained negentropy values 

that reflect this periodicity. Both functions eq. (5a) and (5b) 

have strong periodical components, see Fig. 4(c), and 

demonstrate oscillations which period can be correctly 

determined using a Fast Fourier Transform [22], as 

approximately 62 frames. Function (5b) is again more stable 

and provides better automatic period estimation. The results of 

the statistical method agree with those of the temporal 

methods, cp. Fig. 3.

A common denominator of the results shown is that the 

proposed negentropy-based technique can help in determining 

frames when the observed feature is unreliable (periodic or 

pulse flicker, noise, etc.). Since both eq. 5a and 5b are only 

relatively rough approximations of negentropy, there is no 

wonder they do not provide the same values, especially when 

a negentropy is relatively high. As expected, when a 

negentropy is low, the feature probability distribution is closer 

to a Gaussian so both approximations would give similar 

results. Generally, eq. (5b) provides better performance. It is 

more stable and has less fluctuations. Hence is potentially 

more suitable for automatic thresholding. 

 

2

ftp://pets.rdg.ac.uk/PETS2001/DATASET1/TESTING/CAMERA1_JPEGS/ 
4. FEATURE GENERATION AND MOTION 

DETECTION 

We shortly describe our motion detection method proposed 

in [17]. It is based on change analysis of texture vectors 

computed for 3D, spatiotemporal (sp) blocks. In our previous 

paper [11] we have shown that the use of sp texture vectors of 

3D blocks in the framework of Stauffer and Grimson [14] can 

improve the detection of moving objects while potentially 

cutting back the processing time due to the reduction of the 

number of input vectors per frame. Our experimental results in 

[17] (videos be viewed on [12]) show that our motion 

detection technique leads to further performance 

improvements. 

4.1 Video representation with spatiotemporal 

(sp) texture vectors

We represent videos as three-dimensional (3D) arrays of 

gray level or monochromatic infrared pixel values gi,j,t at a 

time instant t and a pixel location i, j. A video is characterized 

by temporal dimension Z corresponding to the number of 

frames, and by two spatial dimensions, characterizing number 

of pixels in horizontal and vertical direction of each frame. 

We divide each image in a video sequence into disjoint 

NBLOCK× NBLOCK squares (e.g., 8x8 squares) that cover the 

whole image. Spatiotemporal (3D) blocks are obtained by 

combining squares in consecutive frames at the same video 

plane location. In our experiments, we used 8x8x3 blocks that 

are disjoint in space but overlap in time, i.e., two blocks at the 

same spatial location at times t and t+1 have one square in 

common. 

The fact that the 3D blocks overlap in time allows us to 

perform successful motion detection in videos with very low 

time frequency, e.g., in our experimental results [12] videos 

with 2 fps (frame per second) are included. The obtained 3D 

blocks are represented as 192-dimensional vectors of gray 

level or monochromatic infrared pixel values. We then zero 

mean these vectors and project them to three dimensions using 

principal component analysis (PCA). The obtained 3-

dimensional vectors form a compact spatiotemporal texture 

representation for each block. The PCA projection matrices 

are computed separately for all video plane locations (a set of 

disjoint 8x8 squares in our experiments). 

The blocks are represented by N-dimensional vectors bI,J,t, 

specified by spatial indexes (I,J) and time instant t. Vectors 

bI,J,t contain all values gi,j,t of pixels in the corresponding 3D 

block. 

To reduce dimensionality of bI,J,t while preserving 

information to the maximal possible extent, we compute a 

projection of the normalized block vector to a vector of a 

significantly lower length K<<N using a PCA projection 

matrix PK

I,J computed for all bI,J,t at video plane location (I,J). 

The resulting sp texture vectors * bI,J ,t = PK

I,J*bI,J,t provide a 

joint representation of texture and motion patterns in videos 

0 500 1000 1500 2000 2500 3000 0

1

2

3

4

5

6

7

8

Function A

Function B

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 0

1

2

3

4

5

6

7

8

Function A

Function B

0 200 400 600 800 1000 1200 1400 1600 1800 2000 0

1

2

3

4

5

6

7

8

Function A

Function B

(a) 

(b) 

(c) 

Figure 4. Estimated negentropy per frame of each video 

using (eq. 5a) in red and (eq. 5b) in blue for (a) Campus 

1; (b) Campus 3; (c) Temple 2 videos. 
and are used as input of algorithms for detection of moving 

objects. We used K=3 in our experiments. 

To compute PK

I,J we employ the principal values 

decomposition following [4,5]. A matrix of all normalized 

block vectors bI,J,t at video plane location (I,J) is used to 

compute the N×N dimensional covariance matrix SI,J. The 

PCA projection matrix PI,J for spatial location (I,J) is 

computed from the SI,J covariance matrix. The projection 

matrix PI,J of size N×N represents N principal components. By 

taking only the principal components that corresponds to the K

largest eigenvalues, we obtain PK

I,J. 

4.2 Moving objects detection based on local 

variation

The assumption of the proposed technique is that the 

variation of location vectors—corresponding to the same 

location within a small number of consecutive frames— will 

increase if the vectors correspond to a moving object. In 

practice, for each location (x,y), we consider vectors 

b x y t−W b x y t−W + b x y t b x,y,t+W * , , * , , 1 * , , * , ,K, ,..., 

corresponding to a symmetric window of size 2W+1 around 

the temporal instant t. For these vectors, we compute the 

covariance matrix Cx,y,t . We assign the largest eigenvalue of 

Cx,y,t , denoted as Λx,y,t, to a given spatiotemporal video 

position to define a local variance measure, which we will 

also refer to as motion activity 

ma(x,y,t) = Λx,y,t . 

The larger the variance measure ma(x,y,t), the more likely is 

the presence of a moving object at position (x,y,t). Finally, we 

label each video position as moving or stationary 

(background) depending whether the motion activity is larger 

or smaller than a suitably defined threshold. We use a 

dynamic thresholding algorithm (described in Section 2) to 

determine the threshold value at position (x,y,t) based on the 

history of ma(x,y,s) values over time (s=1, ..., t-1). 

5. CONCLUSIONS 

In this paper, we proposed and evaluated two methods to 

monitor the reliability of features applied in video surveillance 

and motion detection. The methods have been evaluated on 

real-life surveillance videos. Both methods correctly identified 

time intervals when an observed feature becomes non useful 

for motion detection (e.g., due to flicker, artifacts introduced 

by compression algorithm, etc.). The proposed methodology is 

potentially applicable to other domains where unsupervised 

learning is performed under open-world assumption (where 

we cannot anticipate all the events which could occur during 

the operational life of an automated intelligent system). 

6. ACKNOWLEDGEMENTS 

D. Pokrajac has been partially supported by NIH-funded 

Delaware Biomedical Research Infrastructure Network 

(BRIN) Grant (P20 RR16472), and DoD HBCU/MI 

Infrastructure Support Program (45395-MA-ISP Department 

of Army). 

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Visual Surveillance and Performance Evaluation of Tracking 

and Surveillance (VS-PETS), October 2003.

[12]R. Miezianko, L. J. Latecki, D. Pokrajac. Link to test 

results. http://knight.cis.temple.edu/~video/VA 

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Regazzoni, eds., Video-Based Surveillance Systems, Kluwer 

Academic Publishers, 2002. 

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Detection Based on Local Variation of Spatiotemporal 

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1973.
A Framework for Measuring Tracking Performance 

of a Sensor Network 

K Madhava Krishna Henry Hexmoor 

Dept. of Computer Science and Computer Engineering 

University of Arkansas 

Fayetteville, AR 72701 

mkrishna@uark.edu hexmoor@uark.edu

Abstract: A framework and analysis for a 

distributed sensor network based surveillance 

system is presented here. In a previous effort [1] 

we have presented methodologies for 

coordination and decision-making amongst 

sensors for tracking targets while in [2] we 

presented the results of endowing the sensor 

network with autonomy. Sensors monitor targets 

that crisscross a rectangular surveillance zone. 

When a sensor pursuits a target it leaves areas 

unguarded through which other targets can get 

past undetected. In this paper we presents a 

methodology that computes the tracking time for 

a sensor that guarantee detection of a required 

fraction of the targets expected to crisscross its 

home area to an arbitrary probabilistic threshold. 

The home area of the sensor is the area guarded 

by it when it is stationed at its home position, its 

default position when it is not in pursuit of a 

target. Simulations are presented that 

corroborate with the probabilistic model 

developed and hence vindicate its correctness. A 

framework for extending the probabilistic model 

to a system where multiple sensors guard the 

same area is also presented. 

1. Introduction 

This paper describes a methodology that 

guarantees probabilistic completeness for sensors 

that track targets in a multi-sensor setting. Each 

sensor guards in its default stationary state an area 

called the home area of the sensor. For a sensor 

j s , its home area is denoted by H j . The robots 

perform surveillance over a rectangular (square) 

surveillance zone. The surveillance zone is 

divided into number of square shaped cells as 

shown in figure 1 for the sake of modeling. The 

figure shows the sensors placed in their home 

positions. The radius of vision of the sensor 

equals the length of the diagonal of the cell. 

However the sensor only considers those targets 

that lie within its four neighboring cells as targets 

within its field of vision. This area representing 

its field of vision in its home position is also 

called as the home area of that sensor for the 

remaining of this paper. The home area of each 

sensor is depicted by thick squares. The 

simulation environment used for testing our 

strategies has been developed through Borland’s 

JBuilder IDE on the Java platform. 

A sensor allocates itself to one of the targets 

within its field of vision through a resource 

allocation process modeled through fuzzy rules 

[1]. The sensor further decides if it would monitor 

the target by remaining stationary or by pursuing 

(tracking) it. When a sensor tracks a target it 

leaves areas in its home position unguarded. The 

tracking time for a sensor j s , denoted by j t

represents the time for which the target would be 

away from its home position H j . The tracking 

time can be modulated based on the fraction of 

the number of targets that a sensor is expected to 

detect within a probabilistic threshold. If NT

ˆ

denote the number of targets expected to 

Figure 1: The rectangular surveillance zone with

sensors depicted as circles ensconced in their home

positions. The home area of each sensor is denoted

by thick squares 
crisscross H j within a temporal window Γ and 

f be the lower bound on the fraction of the 

number of targets, NΓ

ˆ , to be detected and Ω

represent the threshold the paper presents a 

framework for computing = (Γ ,Ω) ˆ , , j NT t g f . 

Here g is a function that guarantees that at-least 

a fraction f of the targets, NΓ , are detected to a 

probabilistic guarantee of Ω . In other words 

g : P(n ≥ f ⋅ Nˆ

Γ ) ≥ Ω , where P is the 

probability computation over the random variable 

n that denotes the number of targets detected. 

The rest of the paper is organized as follows. 

Section 2 presents the current work in the context 

of similar works found in the literature. Section 3 

presents the formulation of the methodology and 

section 4 depicts the efficacy of the methodology 

in simulations. Section 5 extends the formulation 

to an environment where multiple sensors are 

placed with the responsibility of guarding the 

same home area. Section 6 concludes and 

provides further scope of this work. 

2. Background Review 

The problem of multi sensor surveillance involves 

detection of multiple intrusions and/or tracking 

through coordination between the sensors. 

Detection and target tracking has been researched 

from multiple viewpoints. Some efforts have 

focused on the problem of identifying targets 

from a given set of data through particle filters [3, 

and probabilistic methods [4]. The problem of 

data association or assigning sensor 

measurements to the corresponding targets were 

tackled by Joint Probabilistic Data Association 

Filters by the same researchers such as in [4]. 

Kluge and others [5] use dynamic timestamps for 

tracking multiple targets. Krishna and Kalra [6] 

presented clustering based approaches for target 

detection and further extended it to tracking and 

avoidance in [7]. The focus of these approaches 

has been on building reliable estimators and 

trackers. They do not use distributed sensors and 

are not directly useful for the problem of large 

area surveillance. 

In the context of distributed task allocation and 

sensor coordination Parker [8] proposed a scheme 

for delegating and withdrawing robots to and 

from targets through the ALLIANCE architecture. 

The protocol for allocation was one based on 

“impatience” of the robot towards a target while 

the withdrawal was based on “acquiescence”. 

Jung and Sukhatme [9] present a strategy for 

tracking multiple intruders through a distributed 

mobile sensor network. Lesser’s group have made 

significant advances to the area of distributed 

sensor networks [10] and sensor management 

[11]. In [9] robots are distributed across a region 

using density estimates in a manner that facilitates 

maximal tracking of targets in that region. The 

decision for a robot to move to another region or 

to stay in its current region is based on certain 

heuristics. The authors of this paper present their 

scheme for resource allocation and coordination 

in a distributed sensor system through a set of 

fuzzy rules in [1] and further analyze the behavior 

of system by varying the autonomy of the sensors 

in [2]. 

In none of the above efforts is a strategy for 

guaranteeing some form of completeness is 

presented. This paper is unique from other efforts 

in multi-sensor systems in that it offers a tracking 

strategy for sensors that modulates their tracking 

time such that a required number of targets are 

detected within probabilistic guarantees. The 

authors in [12] present a framework that provides 

for meeting a targeted search time within 

probabilistic guarantees for a cooperated UAV 

search. However the computations and the basis 

for their framework is disparate from this effort 

and is presented for a different application and 

motivation. 

3. The Methodology 

Targets are modeled percolating in a Poisson 

fashion at the rate λ through each cell, which has 

one of its edges on the boundary or the perimeter 

of the surveillance area. For a surveillance zone 

such as in figure 1 consisting of six cells along 

each side of the perimeter, the rate of entry is 

6λ . λ is fixed at 0.1for all the examples 

discussed in this paper. Then the apparent rate at 

which each sensor would see a target, λSJ

provided it is stationary is given by the following 

approximation: 

∑=

=

P

k

k

SJ

1 π

θ λ λ , where, θ k is the angle 

subtended from the point where the target enters 

the boundary at the home position of sensor sj . 
Since the entry points of the arriving targets are 

not known a-priori, θ k is computed assuming 

that the target infiltrates at the midpoint of the cell 

edge that coincides with the perimeter of the 

zone. In the figure below (figure 2) the targets are 

assumed to enter at points p1, p2, p3, ... along the 

perimeter of the surveillance zone. For the sensor 

centered at ‘b’, the angle subtended by the target 

entering at p4 is shown marked θ . This angle 

covers the span of all the targets that will cross 

the region of surveillance of the sensor at ‘b’ by 

targets entering at p4. The total span of the angle 

for a target entering at all those points is 

π radians or in other words all targets that enter 

the surveillance zone have to necessarily be 

within a span of π radians from the point of entry 

for them to be within the surveillance zone. 

Let j t be the time for which a sensor sj is away 

from its home position in pursuit of a target as 

mentioned in section 1. We compute the apparent 

time Ta (the time for which a target that would 

have been in the field of vision of sj had sj been 

stationary at its home position perceives sj to be 

away) as: 

( ) 













+ − >

≤

=

∫

∫ κ

κ κ κ

κ

κ

κ

T

j

t

T

t

j

a

dt t T t T

T

t

dt t T

T

t

T

j

j

0

2

0

2 2 ; 2

2 ; 2

(1) 

Here, κ is the fraction of the home area left 

unguarded by sj as it moves away from its home. 

The upper limit of the integral Tκ denotes the 

time at which the sensor leaves its original area 

completely unguarded. If Tesc represents the 

average time for which a target stays in the home 

area of a sensor, the probability that a target is 

detected by a sensor is given by: 

a

esc

T

T

p = . (2) 

Let n be the random variable denoting the 

number of detections made over a temporal 

window Γ as before. The probability of detecting 

exactly k of the NΓ targets expected to arrive in 

Γ is given by the familiar binomial distribution: 

( ) ( ) k N k

p p k

N P n k X N Γ −

Γ

Γ − 













 = = = ˆ

1 ˆ ˆ

Here X is a Poisson random variable that 

measures the number of targets arriving. The 

resultant probability of detecting k such targets 

then becomes 

( ) ( ) ( ) Γ = Γ P n = k = P n = k X = Nˆ ⋅ P X Nˆ

It can be shown that the above resultant 

probability once again has a poisson distribution 

with parameter λSJ p . Hence the probability of 

detecting k targets has the representation 

( ) !

( )

k

p P n k e

k

−λSJ p λSJ = = (3). 

The tracking time j t is eventually computed by 

making use of equations (1), (2) and (3) and that 

which would satisfy the following guarantee 

condition: 

P(n = k ≥ f ⋅ Nˆ

t) ≥ Ω (4) 

Since double precision arithmetic does not allow 

computation of factorials beyond 20 the normal 

approximation to poisson distribution is used in 

our computations. 

4. Simulation Results 

The first objective is to evaluate empirically the 

validity of equation (2) that ascertains the 

probability of detecting a target by a sensor while 

it is in motion. For this purpose a single cell 

environment with one sensor such as in figure 4 is 

Figure 2: Targets are modeled as entering at

locations p1, p2, ..., p4 at the midpoints of the cell

edges that coincides with the perimeter of the zone. 
considered. Targets are introduced in poisson 

fashion at the midpoints of the four boundaries of 

the cell. The sensor’s home position is at the 

center of the cell. The wandering time j t is 

calculated for a given value of Ω and f . The 

sensor is away from its home position for j t units. 

The sensor does not track a particular target. It is 

merely away from its home position. The number 

of targets that crisscrossed the cell during this 

time interval and the number of those detected 

were recorded. 

The results are tabulated in table 1. The first 

column represents the desired fraction of the 

targets that need to be detected and the second the 

minimum probabilistic threshold of detecting the 

fraction. The third column is the actual fraction of 

the targets detected averaged over twenty runs. 

The fourth column signifies the relative frequency 

of times a fraction greater than or equal to the 

desired fraction was detected. The fourth column 

is then a means of evaluating whether the desired 

probabilistic threshold was obtained. If the 

desired fraction to be obtained is 0.6 and 

thirteen times out of twenty a fraction more than 

0.6 was detected, the entry in the last column of 

the table is 0.65 that signifies the required 

performance was met. It is seen that the average 

obtained fraction is above the desired fraction 

whenever the minimum probabilistic threshold is 

high indicating that the desired fraction was 

detected in most of the runs as entailed by the 

threshold. The average fraction obtained is lesser 

than the desired fraction when the desired 

probabilistic threshold is low. This is indeed 

expected as a low desired threshold indicates that 

the sensor is entailed to detect the desired fraction 

of targets only in a few of those twenty runs. The 

relative frequencies in the fourth column also do 

not fall significantly below the desired minimum 

probabilistic threshold in any of the runs. That the 

relative frequency is within 5 −10% of the 

desired threshold in all the runs validates the 

probability definition of equation (2) and the 

computation of apparent time in equation (1). 

In simulations Tesc is computed as the average of 

the minimum and maximum a target is within the 

home area of a sensor. The minimum time is the 

time taken by the target to traverse half the edge 

of a cell. The maximum time is the time taken to 

traverse from midpoint of a side to the farthest 

opposite vertex of the cell. Similarly Tκ is the 

average of the minimum and maximum time 

taken by the sensor to result in its home area 

becoming completely unguarded. The details of 

computing Tκ are omitted here for brevity. 

Table 1: Tabulation of the results obtained for the 

environment of figure 4 for different desired fraction 

and threshold values. 

The framework developed in section 2 is now 

tested for an environment shown in figure 1 with 

multiple sensors. Each sensor tracks targets such 

that the probabilistic guarantee is maintained with 

respect to its home area. The overall quality of 

track (QoT) at the end of a simulation interval Γ

is defined by: 

( )

( ) ∑

Γ

Γ = Γ

Γ =

N

i i

i

c

d

N QoT

1

1

 (5) 

Here NΓ is the actual number of targets that 

crossed the surveillance zone in Γ . The 

Desired 

minimum 

fraction 

( f ) 

Desired 

minimum 

probabilistic 

threshold 

(Ω ) 

Obtained 

average 

fraction 

(20 runs) 

Obtained 

relative 

frequency 

(20 runs) 

0.9 0.9 0.91 0.95 

0.9 0.1 0.23 0.05 

0.6 0.9 0.73 0.85 

0.6 0.1 0.38 0.2 

0.4 0.6 0.42 0.65 

0.4 0.4 0.32 0.3 

0.1 0.9 0.28 1 

0.1 0.1 0.08 0.2 

Figure 4: A single cell environment used for

validating the definitions of equations (2) and (1).

The bigger circle denotes the sensor and the

smaller circles the crisscrossing targets introduced

in poisson fashion. 
numerator di indicates the number of sensors 

that detected the target i in Γ while the 

denominator, i c denotes the number of sensor 

home areas that the target i had got past in Γ . 

Essentially QoT is an average measure on 

whether a target that crossed the home area of a 

sensor was detected by that sensor with the 

difference that the QoT would also reflect cases of 

targets that are detected by sensors whose home 

area it did not cross elsewhere in the surveillance 

zone. In the summation of (5) if the fraction 

i

i

c

d

exceeds unity it is clipped to unity. This is 

done since a fraction greater than unity tends to 

offset for fractions less than unity and does not 

reflect those cases. A stricter definition of QoT

that specifically captures the number of targets 

missed by a sensor that crossed its home area is 

given by: ∑=

=

NS

j cj

dj

S n

n

N QoT

1

1

 (6). 

Here NS denotes the total number of sensors in 

the environment, ndj denotes the number of 

targets detected by the sensor among those that 

had visited its home area H j , while ncj is the 

number of targets that had been through H j . 

Thus 

c

d

n

n

 represents the fraction of the targets 

that entered a sensor’s H j and were detected by 

it and can never exceed unity. However we found 

that at the end of the simulation interval the 

values as computed by (5) and (6) vary only 

marginally. Hence in this paper the results of QoT

are those computed as in (5). 

In the simulations that follow a sensor leaves its 

environment in pursuit of a target. Sensors can 

reallocate themselves to other targets during the 

course of a track as dictated by the resource 

allocation strategy. The time j t for a sensor is 

updated after every fixed number of samples 

based on the fraction of the targets that were 

detected thus far and the fraction that need to be 

detected in the remaining time window to meet 

the objective of (4). 

Figure 5 shows a snapshot of a simulation run. 

The bigger circles represent the sensors and the 

smaller circles the targets. The dashed rectangles 

enclosing the sensor and target identify the 

sensor-target pair (the target to which the sensor 

has allocated itself to). It is to be noted while a 

sensor tracks a target it also detects all other 

targets within its field of vision. Currently the 

problems of data association and target occlusion 

are not considered. 

4.1 Analysis: 

Figure 5a shows two graphs that plot rf , the 

fraction remaining and wander time, j t , along the 

y-axis. In both the graphs the abscissa denotes the 

time in samples. Sampling measurements on rf , 

j t are done once in every ten cycles of a 

simulation run. The total number of simulation 

cycles is 150 or in other words Γ = 150 in these 

simulations. Each cycle is repeated every 500ms. 

The graphs cover the entire simulation run of 150 

cycles or 15 samples of measurements. The plot 

of figure 5b depicts QoT on y-axis and sample 

time on x. Both graphs 5a and 5b are for a 

simulation run with parameter f = 0.8, Ω = 0.75 . 

The graphs of figure 5a are for one of the sensors 

of figure 5 only the graph of 5b depicts QoT of 

the entire system. Graphs in figure 5c and 5d have 

the same connotations as in figures 5a and 5b 

except that they are for parameters 

f = 0.8, Ω = 0.3 . The horizontal dashed line in 

the graph of 5b and 5d indicate the desired 

Figure 5: A snapshot of a simulation run. The dotted

rectangles enclosing a sensor-target pair indicate the

target to which that sensor is currently allocated to.

Sensors are shown by larger circles while targets are

depicted smaller 
fraction of target fraction of targets, f , expected 

to be detected at the end of the simulation. Since 

QoT as defined in (6) computes the fraction of 

targets detected averaged across all the sensors in 

the system, the horizontal line serves as an 

indicator if the QoT was achieved or not. 

For Ω = 0.75 the track time is modulated such 

that the desired fraction f averaged over all 

sensors is detected at the end of a simulation run 

for majority of such runs. Figure 5b corresponds 

to one such run where the track quality at the end 

of the simulation is 0.85 and is above the 

expected criterion of 0.8 and lies above the 

horizontal. Figure 5d corresponds where the 

QoT at the end of the simulation does not achieve the 

desired fraction. This is expected for a run with 

Ω = 0.3 where most of the runs are not required 

to detect a fraction greater than 0.8. 

For a marginal increase in rf in the top plot of 

figure 5a the corresponding decrease in j t is 

steeper in figure 5a when compared with figure 

5c. The decrease in wander time j t as rf is less 

steep in 5c than in figure 5a. For a given f the 

variations in j t are due to the variations in Ω . A 

higher Ω entails that the sensor cannot move too 

far away from its home due to lower values of j t . 

As the sensor moves away from its home and 

misses targets the required remaining fraction to 

be detected rf may tend to increase. In such a 

case the decrease in wander time also tends to be 

steeper for a similar increase in rf for a higher 

Figure 5a: The top graph shows rf plotted against

sample time while the bottom graph is a plot of j t

against samples. The plots are for a simulation

such as in figure 5 run with f = 0.8, Ω = 0.75

Figure 5b: A plot of track quality QoT . The dashed

horizontal line denotes the desired fraction of the

total targets that need to be detected. 

Figure 5c: Graph same as figure 5a for

parameters f = 0.8,Ω = 0.3

Figure 5d: Graph with same connotations as

figure 5b for parameters f = 0.8,Ω = 0.3. At

the end of simulation time the track quality is

below the horizontal line indicating that

performance criterion was not met 
Ω . A steeper increase translates as quicker 

returns to home by the sensor to detect more 

targets. 

6 Extension to Multi-sensor 

Surveillance 

The benefits of having more than one sensor 

guard the same home area is now considered. For 

example let each of the home area in figure 1 

(shown by thick squares) be guarded by 3 sensors. 

One such area is shown in figure 6. 

It can be shown that Tκ , the time taken by the 

sensor to leave the area completely unguarded is 

the same on an average for all the three sensors. 

Let the sensors be labeled as A, B and C. The 

probability that sensor A detects a target is 

denoted as p A and has the same form as (2). 

Similarly the individual probabilities of detection 

for sensors B and C are denoted as pB and pC . 

Since Tκ and hence Tapp are the same for the 

three sensors p A = pB = pC . The probability 

that at-least one of the sensors detect a target is 

given by p = p A U pB U pC . Determining p

from equations (3) and (4) and along with the 

condition p A = pB = pC leads to the following 

cubic in the individual probability of a sensor: 

3 3 0 3 2p A − p A + p A − p = (7). 

The solution to the cubic solves the individual 

probability of a sensor detecting a target. 

Figure 7a shows two graphs. The top graph 

depicts the individual probability of a sensor 

detecting a target for a fixed Ω (here 0.7) and 

varying f . The lower graph plots j t versus 

f for a constant Ω (here 0.7). Each of these 

graphs shows two plots. The plot with a dashed 

line corresponds to the case where a single sensor 

guards an area. The plot with solid line 

corresponds to the case where multiple sensors 

guard an area. The graphs indicate that the 

individual probability of detection is consistently 

lower when multiple sensors guard an area than a 

single sensor guarding and the wander time is 

correspondingly high for a multi-sensor case. 

Hence a sensor can wander away from its home 

area for a longer duration when if there are more 

than one guarding its home area. In [2] we have 

shown longer tracking time enhances 

performance criteria based on median and mean 

number of detections of targets. 

7 Conclusions: 

A framework that provides for probabilistic 

guarantees for a multi-sensor based multi-target 

tracking system is provided here. Sensors 

modulate their tracking time based on the desired 

fraction of targets that need to be detected and the 

minimum probabilistic threshold of detection. 

Simulation results corroborate the efficacy of the 

formulation of the scheme for probabilistic 

guarantees. Extension of the scheme to multiple 

sensors guarding the same area enables longer 

tracking time for a sensor and hence better 

Figure: An area guarded by three sensors, one

at the center and two at the corners 

Figure 7a: Plots of individual probability and

wander time against varying values of desired

fraction f . Solid lines are plots corresponding to

a single sensor while dashed lines correspond to

multi sensor case
performance based on mean and median number 

of detections. 

References: 

[1] K Madhava Krishna, H Hexmoor and S Pasupuleti, 

“A Surveillance System Based on Multiple Mobile 

Sensors”, to appear in Proceedings of FLAIRS, 2004, 

Special Track in Sensor Fusion. 

[2] K Madhava Krishna, H Hexmoor and S Pasupuleti, 

“Role of Autonomy in a Distributed Sensor Network”, 

to appear in Proceedings of ICAI, 2004. 

[3] D Schulz; W Burgard, D Fox and A Cremers, 

“Tracking multiple moving targets with a mobile robot 

using particle filters and statistical data association”, 

IEEE International Conference on Robotics and 

Automation, 1165-1170, 2001 

[4] D Schulz and W Burgard, “Probabilistic state 

estimation of dynamic objects with a moving mobile 

robot”, Robotics and Autonomous Systems, 2001. 

[5] B. Kluge, C Kohler and E Prassler, “Fast and robust 

tracking of multiple objects through a laser range 

finder”, IEEE International Conference on Robotics 

and Automation, 1165-1170, 2001 

[6] K Madhava Krishna and P K Kalra, “When does the 

robot perceive a dynamic object”, Journal of Robotic 

Systems, 19(2), 2002 

[7] K Madhava Krishna and P K Kalra, “Detection 

tracking and avoidance of multiple dynamic objects”, 

Journal of Intelligent and Robotic Systems, 33(4): 371-

408, 2002 

[8] L Parker, “Cooperative robotics for multi-target 

observation”, Intelligent Automation and Soft 

Computing, 5[1]:5-19, 1999 

[9] B Jung and G.S. Sukhatme, “Multi-Target Tracking 

using a Mobile Sensor Network”, Proc., IEEE Intl. 

Conf. On Robotics and Automation, 2002 

[10] B Horling, R Vincent, R Miller, J Shen, R Becker, 

K Rawlins, and V Lesser, “Distributed Sensor Network 

for Real Time Tracking”, In Proceedings of the 5th 

International Conference on Autonomous Agents:. 417-

424, 2001. 

[11] B Horling, R Miller, M Sims, and V Lesser, 

“Using and Maintaining Organization in a Large-Scale 

Distributed Sensor Network”, In Proceedings of the 

Workshop on Autonomy, Delegation, and Control, 

(AAMAS 2003). 

[12] P Vincent and I Rubin, “A Framework and 

Analysis for Cooperative Search Using UAV Swarms”, 

Proceedings of SAC’04, March 14-17, Nicosia, Cyprus 
1

Goal-Oriented Intelligence in Optimization of Distributed 

Parameter Systems 

Shlomo Orr, MRDS, Inc. (PERMIS, 2004) 

Abstract 

Models of complex systems can be differentiated by their ability to reproduce or generate 

system behavior, by their prediction power, by their robustness, or, conversely, by their 

sensitivity to inputs and parameters; by their uncertainty (if captured); and by their 

intelligence. Even the term “prediction” is not unique. First, a first-principle (physically 

based) distributed parameter model could be an excellent predictor if (a) it captures the 

main system behavior, and (b) its parameters and inputs are known accurately; otherwise, 

it would fail, possibly drastically. Second, predictive power depends on the data, on the 

goal, and on the time scale. For example, scheduling of pumping and injection in an 

oilfield for maximum profit over the next 5 years; or pumping from a contaminated 

aquifer in order to maintain certain (low) concentration at a compliance point for the next 

20 years, vs. prediction of plume migration in groundwater towards a nearby river, over 

time: in each case, the model has a slightly different expected function, as well as 

different intelligence type. The paper reviews the recent developments in subsurface fluid 

flow management such as optimization of oil production and groundwater remediation 

(both sharing similar practices, though for different purposes) as a continuous struggle to 

increase intelligence by (a) adapting new tools such as artificial intelligence and dynamic 

stochastic control; (b) attempting to integrate these tools; and (c) reducing uncertainty. 

Although the systems discussed seem specific to the (mathematical) geosciences 

(specifically to oil reservoirs and contaminated aquifers), and although these systems are 

very different from man-made machines, similar rigid structure and reliance on 

differential-integral calculus, as well as the serial processing, knowledge evolution, and 

uncertainty propagation from one discipline to the next exist in most science and 

engineering fields, and so does the need for a paradigm shift. Given the need in adaptive, 

intelligent control/planning/optimization of such systems, the progress of these 

segregated efforts towards a multiresolutional decision support system is inevitable, 

highly desirable, and highly promising. However, we are still facing the challenge of 

performing and defining optimal integration between PDE models and multiresolutional 

representations, and since such integration depends on model quality and data quantity 

and quality, this is an adaptive integration process as well. One criterion for such 

“optimal” integration would be uncertainty reduction (resulting from the integrated MR 

system), which brings up yet another challenge: to define the metrics for uncertainty 

reduction. 
2

1. Introduction

Management of distributed-parameter systems, particularly where complex natural 

processes intersect with human industrial practice and theoretical knowledge, is 

extremely difficult to analyze and optimize. From a knowledge organization perspective, 

this area of practical knowledge is in disarray. For example, knowledge in the petroleum 

industry relates to many scales of representation, yet this fact is not taken into account in 

an organized manner. 

Indeed, the oil industry is a live example of the need to integrate multiple disciplines 

presently not integrated, including huge volumes of raw data (particularly in geophysics) 

and multiple computational and conceptual models of geology, geophysics, and reservoir 

dynamics. Although the need in unification of the bodies of knowledge in these 

disciplines and the associated (tremendous) benefits of analysis enhancement capability 

has been widely recognized, progress in this direction has been very slow. The main 

reason for this is the rigid, segregated, serial process of knowledge and model building – 

from geophysical signals to simulation-optimization of fluid dynamics in porous media – 

a process that has evolved naturally during the last century, where the simulator has 

become the focal junction where all the knowledge and understanding of the physical 

processes and material properties are being filtered and concentrated in the form of 

partial differential equations (PDE that describe mass balance of oil, water, and gas in 3D 

space) whose coefficients (or distributed parameters) suppose to capture the physicalchemical properties of the medium on a particular scale, everywhere in the modeled 

subsurface/reservoir domain, assuming some “known” boundary conditions and initial 

conditions. In the following, we will use subsurface flow systems, particularly, oil 

reservoirs, as examples of managed, distributed parameter systems. 

Oil reservoirs are complex systems on all scales. Decisions such as pumping and 

injection (schedule and rates), new well placement, and (directional) drilling in an active 

oil field, are typical of the complex relationships between reservoir characterization and 

oil field/reservoir management. The solutions to such problems involve a complex system 

of multiphase flow equations (linked PDE) in a heterogeneous domain (reservoir), as well 

as economical factors such as short-term and long-term oil price, worth of information, 

inventory/storage/delivery, cost of drilling, maintenance, production, etc. Well drilling 

and construction equipment are costly and cannot be afforded as frequently as necessary, 

while prevalent information gaps render decision-making uncertain and hence, risky. 

Yet, the advantages of reservoir simulations should not be underestimated either. 

Models or simulators based on PDE solutions provide physical insight into various 

important flow phenomena, as well as the general behavior of the fluid movements in the 

reservoirs, under scarcity of spatial data typical of both old and young reservoirs, 

particularly the latter. The ability to capture the essence of the complex physics behind 

the reservoir responses to pumping and injection is the strength of the simulator and the 

essence of its intelligence. However, this strength could promptly become its weakness 

where (a) natural geological heterogeneities on certain scales are being missed, or (b) 

physical/chemical/thermodynamic processes are being missed (e.g., leaching 

geochemistry; instability of the oil-water interface), or (c) uncaptured (or erroneous) 

boundary conditions, all of which would lead to wrong predictions. In other words, 

wherever an essential physical phenomenon on any scale is being missed, the simulator 
3

looses its intelligence, i.e., its ability to predict short-term reservoir responses and longterm oil reserves and revenues. 

The main question we attempt to address in this paper is how to merge the 

advantages and use the intelligence of existing models and interpretations in a 

comprehensive intelligent system that could take advantage of such physically based 

intelligence, while eliminating its limitations. In order to answer this question, we first 

need to understand the structure and limitations of current approaches to 

optimization/control of subsurface fluid flow and solute transport. The reader could 

notice that although the problems discussed here seem to be specific to optimization of 

oil production and groundwater remediation, similar rigid structure and reliance on 

differential-integral calculus exist in most engineering fields, and so is the need for a 

paradigm shift when planning/control/optimization become the focus. Yet, we should 

also keep in mind some major difference between the geosciences (or natural systems in 

general) and man-made machines. In hydrogeology and oil reservoirs, we deal with 

multiphase flow in heterogeneous formations, with transient flow and transport 

phenomena occurring on all scales, with nonlocal dependency on (unknown) fluid flow 

everywhere. However, whenever we focus on operations’ scheduling, feedback and feedforward, this complex system becomes similar to other complex operations; finding a 

new well location, however, requires considering the complete heterarchy of transient 

flow phenomena in space, often with major data gaps. Such data gaps challenge all 

models, and consequently, any integration of PDE models with MR knowledge 

representations (and/or MRDS). Such integration seems to be data-dependent, and 

requires optimization on its own merit, weighting the robustness, prediction/anticipation 

(goal-oriented) power, the uncertainty associated with different representations, as well as 

uncertainty reduction produced by such integration. 

 

2. Current approaches to simulation-optimization-control of 

distributed-parameter, subsurface flow systems

The cutting edge subsurface fluid management such as oil reservoir optimization and 

groundwater remediation control under uncertainty has been moving in three major 

fronts: (1) operations research (including stochastic models and risk assessment); (2) 

stochastic-dynamic control; and (3) artificial intelligence (AI), particularly artificial 

neural networks (ANN), genetic algorithms (GA), and fuzzy logic (FL). However, under 

the current structure of serial, segregated, and isolated “disciplines” that process the 

information from geophysics/explorations to reservoir characterization, reservoir 

simulations (or flow and transport models in hydrogeology), and optimization/control, it 

is impossible for these three fronts to merge into a unified, integrated approach, nor could 

a major progress in oil field management be made. Under the current paradigm, 

optimization/planning/control of these complex systems have been handicapped by 

uncertainty on one hand, and prohibitive computer power & time requirements on the 

other hand, without benefiting from all available information. 

The typical approach to reservoir characterization and management sketched in 

Figure 1 shows the different subsystems that constitute both exploration and production. 

The figure is highly simplified, with many subsystems not shown, such as subdivision of 
4

exploration (remote sensing, surface- and borehole-geophysics; seismic, electrical, 

electromagnetic, micro-gravity, SP, etc); geologic investigations (structural geology, 

geochemistry, lithology, bio-stratigraphy); subdivision of production (well pattern design, 

injection and pumping, gas, water, and displacing fluids); and well construction, - all of 

which are complex, interdependent, and require real time updating and decision making. 

The figure illustrates current model construction and subsequent optimization. 

Blocks 1 and 2, and, to some extent, Block 3 (conceptual model), represent reservoir 

characterization, which plays a crucial role in exploration and subsequent reservoir 

management. Typically, the conceptual model (Block 3) of the reservoir is an undeclared 

part of the simulator; this is where all the geology is filtered, upscaled, and translated into 

the simulator’s parameters, which inherently entails averaging and discarding of 

information (acting as a low-band filter), including small scale features that may be crucial 

(in which case, their large-scale influences would be modeled as different, large-scale 

parameters – e.g., dispersion coefficient). Most of the assumptions and decisions related to 

reservoir representation are made at the conceptual model stage, and are subject to 

modeler’s understanding and experience. 

 Figure 1. A schematic view of current approaches to reservoir optimization. 

Block 4 is the current quantitative “brain” (or predictor), typically a distributedparameter, complex PDE solver that may include several linked PDE with their auxiliary 

constitutive functions (mostly determined in the lab, on a lab-scale), or less commonly, a 

cell model, represented by Ordinary Differential Equations (ODE), implying a larger 

Seismic, gravity, 

electromagnetic,

electric signals 

Excitation 

World

(Oil Field)

Geophysics 1

Seismic processing, 

interpretation, and

modeling 

Geologic model 2

Structural,

Stratigraphy

Sedimentology 

Petrology, Statistics

Simulator 4

(PDE Solver)

Reservoir conceptual 3

model (processing)

Geostatistical modeling

Economic 5

Model (NPV)

Optimization (GA) 6

or Decision Model

Surface 7

Operations

• Scheduling

pumping/injection 

• Well placement

Cuttings from drilling, core samples,

chemistry/mineralogy, bio/fossil, fluids

Pressures, saturations,

chemistry/composition

discharge/injection rates 

Geophysics 1

Well information

Location/configuration

Model (NPV)

MCS/stochastic 4*

 6

Decision Model

• Drilling, construction,

materials, operational costs

• Constraints
5

scale, i.e., lower resolution). Within this computational block, additional analytical forms 

are utilized for computing parameters and constitutive relationships, as well as local 

modeling (e.g., the Buckley-Leverett model of displacement). Ideally, the simulator 

contains multiple analytical models functioning at different time scales, and demonstrates 

processes working at different levels of resolution. However, current models are far from 

this ideal. 

Due to the embedded upscaling and loss of information, feedback from the reservoir 

simulator (4) to the geological model (2) is not reliable, except for special cases where 

certain disparity exists between the measuring window and the scale of the geologic 

feature, and where only a piece of the puzzle is missing (e.g., in well testing with an 

appropriate monitoring system in place, or in dual porosity systems where the rock 

properties are well characterized on all scales). Typical inverse or automatic calibration 

procedures determine some local reservoir-fluid interaction “properties” that fit a 

particular (and hence, uncertain) model. Subsequent interpretations of geologic features 

based on inverse modeling (or calibration of the simulator) are, therefore, speculative. 

2.1 Reservoir Simulations and Groundwater Modeling Problems 

Historically, modeling of fluids flow in porous media using PDE started by Muskat 

in the 1930’s [52, 53]. Until that point, predictions of reservoir behavior over time was 

merely extrapolations from a (local) “production curves” or “well performance models”, 

which describe cause-effect relationships between production, fluid content (oil, water, 

gas), and pressures in producing and injection wells, over time, using curve 

fitting/regression [66]. The introduction of PDE suddenly provided insight and extended 

the prediction power significantly, providing intelligence to an otherwise a black box 

model. This addition of intelligence has had a sweeping effect, and was extended to 

groundwater and multiphase flows in porous media, including geothermal reservoirs, 

unsaturated flow in soils, and contaminant transport in aquifers (e.g., [9]), while it has 

been further reinforced by a rapid development of numerical methods and ever-increasing 

computer power. The success of the numerical model that could explain and predict the 

subsidence of Venice in the early 70’s [84-86] has been used as a live example of the 

ultimate intelligence of this new tool. By the early 80’s, reservoir engineers and 

hydrogeologists have developed numerous numerical models (or simulators), which, with 

the help of new visualization tools and mainframe computers, could both predict and 

visualize the movement of oil, gas, water, and contaminants (in groundwater), with 

ultimate confidence and optimism due to the exponential growth of computer power and 

the prospect of optimal management. However, before long, it has become clear that once 

applied to geological formations on a scale where the heterogeneity cannot be neglected, 

the strength of the PDE-based model becomes its weakness; this sensitivity, overlooked 

and even welcomed initially (because sensitivity to certain inputs and parameters is 

consistent with the physics of the phenomenon), came to haunt the modelers later on; the 

exaggerated expectations have turned into disappointment and distrust. 

How could this be explained? A reservoir simulator based on PDE requires accurate 

definitions of reservoir properties on assumed certain scales, everywhere in the reservoir, 

in order to reliably represent the flow, and predict reservoir responses. Such near-ideal 

conditions could occur in cases where the scales of heterogeneities are much smaller than 

the simulated domain, and given the particular question being asked, such heterogeneities 
6

could be lumped under unique, measurable reservoir characteristics that could be 

assumed uniform on a particular scale. While this could be the case in many sandy 

reservoirs and aquifer, on a certain scale, many more reservoirs and aquifers exhibit nonuniformity on all scales, and thereby, drastically degrade the prediction capability of 

PDE-based models. This has forced reservoir modelers and hydrogeologists to account 

for heterogeneity in any possible way. Due to lack of spatial data, heterogeneity translates 

to uncertainty, and uncertainty translates to randomness, and thus, the PDE become 

random (or stochastic) PDE [e.g., 87], severely complicating and inhibiting prediction 

capability. Moreover, since the uncertainty is on all scales and in all parameters, 

structural model errors add severe, unquantifiable uncertainty to the already uncertain 

solution [58, 54, 82]. Before we reach this bleak conclusion, let us further explore current 

treatment of heterogeneity/uncertainty in reservoir simulations. 

2.2 Dealing with data gaps and uncertainty 

We recognize that knowledge of all reservoir flow properties on all scales 

everywhere in the reservoir is impossible even without considering drilling costs. Due to 

the high cost of drilling, there is typically only sparse information on reservoir behavior, 

while geophysical (esp. seismic) data are by far more abundant. As a separate discipline, 

reservoir modelers have no choice but to rely on geological interpretations and limited 

observations of reservoir behavior, while being forced to average and upscale reservoir 

properties using ad-hoc estimates and geostatistical tools. 

The prevalent method to account for heterogeneity (of reservoir properties) and the 

resulting uncertainty is to treat all the data or interpretations related to one or two 

dominant parameters (typically, saturated permeability) statistically, i.e., transforming 

uncertainty into randomness, typically under the assumptions of underlying joint 

probability distribution (PDF) that (assuming ergodicity) represents space and time as 

well. Once a certain parameter is considered random, the PDE solution becomes random 

(or stochastic) as well, and additional theoretical difficulties emerge [56-58, 87]. This 

approach has been developed and used for the last five decades in different areas of 

science and engineering, including stochastic optimization of oil reservoirs [1, 10-12, 20, 

28, 36, 51, 59, 65-66, 80-81] and groundwater remediation [2, 3, 14-15, 19, 21-23, 25-27, 

31, 39-42, 49, 68-73, 77, 83]. Despite remarkable theoretical advances in this difficult yet 

essential extension of the deterministic approach, developments have been limited to 

simple geometries and far-reaching simplifications. 

The use of Monte Carlo Simulations (MCS), where “equally probable” highresolution worlds (or realizations) are generated and simulated in order to compute 

ensemble statistics has been used extensively in the areas of reservoir simulations and 

hydrogeology (e.g., [56-58]); however, in practice, such a procedure results in enormous 

(if not prohibitive) computational burden for predictions alone, and becomes practically 

prohibitive for optimization, unless far-reaching simplifications are being made (e.g., 

[28]). In addition to these limitations, the traditional stochastic approach suffers from the 

following drawbacks and inconsistencies: (a) it cannot overcome, nor assess the major 

uncertainty in the model structure (which remain rigid); and (b) it leads to additional 

(now statistical) models with new parameters that are also uncertain; (c) using 

interpretations of well tests that assume homogeneity on a “near well” scale as the basis 

for conditional (stochastic) simulations; (d) using a single “dominant” parameter (on a 
7

single scale) as the only random property (otherwise, computations are prohibitive even 

for limited cases); (e) assuming a PDF based on sparse spatial data; (f) assuming 

deterministic boundary conditions despite the significant uncertainty in it; (g) the 

inability to capture the linked physics and chemistry on all relevant scales (thereby, 

missing important phenomena such as front instability (between displacing and displaced 

fluids during enhanced oil recovery, where micro-scale variations trigger and promote 

fingering and bypassing due to capillary and viscosity differences [e.g., 35] and various 

geochemical reactions. Nevertheless, reservoir simulations and groundwater modeling are 

an important basis for approximations, correlations, and physical interpretations, 

including understanding and highlighting of the gaps and limitations of these 

interpretations. 

Further, repeating the MCS chain of simulations and optimization as soon as new 

information arrives is practically impossible under the current scheme. Thus, despite the 

powerful theoretical framework and insight provided by the stochastic approach, this 

approach is yet in infancy, and does not extend beyond a certain definition of parameter 

uncertainty. Indeed, when optimization is attempted, e.g., for a new well placement, the 

computation-intensive stochastic approach becomes impossible, while a partial use of the 

approach (e.g., using only a few Monte Carlo simulations, as in [28, 12, 71], not 

accounting for uncertainty in other parameters, in the conceptual models, and in all 

interpretations and decisions along the path in Figure 1, leads to largely non-optimal 

decisions. If the reduction of intelligence can be measured by the amount of error 

between optimum and non-optimal operation, such a difference implies a significant 

reduction in intelligence gained by physically based models. 

In conclusion, we recognize relationships between uncertainty, model robustness, 

and intelligence; an ideal PDE-based model is highly intelligent in a sense that it can 

predict reservoir behavior at all points in space and time; however, as soon as the model 

structure is inaccurate or model parameters are uncertain, it looses its intelligence to a 

large degree. Practically, this implies that a sensitive model would be “intelligent” as 

long as all necessary data exist and are accurate, but drastically looses its intelligence 

where data are uncertain, inaccurate, or insufficient; on the other hand, a less sensitive 

(more robust) PDE-based model would also be less intelligent to begin with. Thus, we 

seem to face an optimization problem: what model would be the optimal model for a 

particular problem; or better, what combination of models would be optimal in terms of 

data use, (maximum) intelligence, and robustness. 

2.3 Current use of Artificial Intelligence 

Before we answer this question, we should be aware two other sets of models: one 

based on artificial intelligence (AI) methods (also commonly termed soft computing), 

mostly in the context of geologic analysis and oil explorations, and one based on a 

statistical framework, particularly geostatistics and Bayesian statistics. As to AI, tools 

such as artificial neural networks, fuzzy logic, genetic algorithms, and probabilistic 

reasoning, have been used in reservoir characterization [75-76], subsurface flow [29, 63-

64], and well field development and optimization [1, 10-11, 13, 28-30, 59, 62-64]. 

Consistent with the AI approach is the excessive use of geostatistics, such as the search 

for best next well placement described in [30], where the authors bypassed the simulator 

altogether, and used indicator kriging, instead, to interpolate expected production and 
8

make corresponding decisions. Nevertheless, one of the important outcomes from these 

developments is the recognition of the need in integration of methodologies rather than 

using them in isolation [75]. In particular, the need to address the issues of (a) integrating 

information from various sources with varying degrees of uncertainty; (b) finding 

relationships between measurements and reservoir properties; (c) reducing uncertainty 

and risk; and (d) using all of these to optimize reservoir development and management, in 

real time. However, the progress in this direction has been slow, and fragmented results 

still dominate the field. The main reason for this is the need to translate information 

among the subsystems that constitute an oil reservoir, from geophysics to geology, and 

from geology to reservoir flow properties, and perform all of these translations on 

different scales of information, with different geometric and stratigraphic representations. 

These integration problems, and the overwhelming problem of uncertainty due to lack of 

data in the presence of inherent heterogeneity, have been unresolved, to date, with only 

scattered use of the various computational tools for limited characterization and 

prediction purposes; hence, leading to non-optimal management of oil reservoirs, water 

resources, and environmental cleanup (groundwater remediation) operations. 

How could these capable AI models be combined with all other models in an 

adaptive framework that will (a) account for all the information (old and new, without 

initial filtering), and (b) allow continual updating and improvement due to continual data 

accumulation. The challenge is, thus, to integrate various measurements/data and models 

in a comprehensive, flexible, adaptive knowledge representation that will use all the 

available information for optimal decision making in the most intelligent way possible. 

Before trying to answer this question, let us review the third approach to 

control/optimization of subsurface flow and transport problems. One step in that direction 

was made by Rogers and co-workers [63, 64] who ‘trained’ a ANN by using multiple 

deterministic flow and transport simulations of a complex aquifer under a pump & treat 

operation, and later [29] for oil reservoir simulation-optimization, and then used the 

efficient ANN as a replacement (“proxy”) for the cumbersome, slow simulator. Due to 

the limited extrapolation power of the ANN, many model runs were needed for the 

training to cover the expected span of possibilities (in the search space), to enable 

optimization of pumping and injection schedules. Although the method used is 

deterministic, as pointed out by the authors, it could, in principle become stochastic by 

generating multiple realizations and running Monte Carlo simulations (MCS), which, 

however, would result in prohibitive computer power. In other words, since the 

unsupervised ANN used is relatively less intelligent than the PDE models, it was used 

only as a minor auxiliary function. We would like to reverse this ranking of intelligence 

in a way that will enable broader conceptualization and knowledge representation. 

2.4 Applying Dynamic Control 

Dynamic, stochastic control has been used and further developed mainly for 

groundwater remediation purposes, specifically for pump & treat operations, which are 

similar to oil production operations; while the goal in oil production is to maximize 

production profit (over a certain period), the goal of groundwater remediation is to 

maximize extraction of contaminated water from the aquifer over a reduced period. The 

dynamic-stochastic control approach in this field [6-7, 16-18, 24, 32-34, 37-38, 60-61, 

74] is an extension of the more general stochastic control theories of [8, 50, 67, 78-79]. 
9

While under the dynamic control approach, inverse modeling (i.e., updating/calibrating of 

uncertain parameters in a simulator or in a flow and transport model) is done jointly with 

the optimization process (hence, dual control), while feedback control rules enable 

changing of pumping rates (control variables) in response to changing hydraulic heads or 

contaminant concentrations (state variables). The stochastic simulator varies from 

extended Kalman filter to PDE, using perturbation methods and dividing the cost 

function into deterministic and stochastic parts, with the goal of minimizing remediation 

or plume-containment cost while optimizing both sampling and control actions. 

Typically, differential dynamic programming (DDP) is used to compute the deterministic 

control [6] while the solution of the stochastic part of the cost function is obtained 

analytically using stochastic control techniques applied to the governing flow and 

transport equations (PDE), with challenging mathematical derivation that requires a twice 

differentiable cost function. The on-line parameter estimation fed into the flow equation 

enables updating of both state variable estimates and state covariances. In terms of 

formulation of the cost function, the following highlights are worth mentioning: (a) the 

goal is to minimize the average (estimated, probabilistic) cost function; (b) the cost 

function is separable in stages, and according to the dynamic programming approach, 

whatever the initial state and initial decision are, the remaining (future) 

decisions/solutions should constitute an optimal solution based on the current state; i.e., 

the problem is reduced to finding a current optimal control variable, given a cost function 

over the remaining (future) periods, and given the current information state which 

includes all relevant a priori knowledge of the system and its history of observations and 

control; probabilistically, this information state is the conditional probability density 

function of the state at the current period conditioned on all past information; 

consequently, the cost function depends on uncertainty, directly. The two hidden 

elements in this procedure are: (a) the Bayesian approach, and (b) learning (from past 

experience). 

Similar works [24] emphasize the use of all available information to estimate all 

present and future uncertainties, solving the management problem over the designated 

control horizon, applying the optimal control action (pumping or injection) during the 

current time period, and repeating this process at the next decision time, with PDE (flow 

equations) treated as a dynamical state-space system using finite element and finite 

difference techniques, considering (both) transmissivities and boundary conditions 

uncertain, and hence, perturbed in a highly simplified aquifer system, with the goal of 

minimizing pumping (and treatment) costs while maintaining hydraulic heads that 

guarantee containment of the contaminant plume. The results (a) provided insight into 

system response under uncertainty; (b) assessed trade-offs between satisfying goals and 

minimizing uncertainty (based on a simplified uncertainty model); (c) emphasized the 

effect of management decisions at any stage on model predictions in the next step. 

Explicit optimization combined with sensitivity analysis appeared to be an effective 

management approach. Other works [37-38, 60-61] extended the methodology of optimal 

estimation and scheduling of aquifer remediation under uncertainty, by allowing more 

complexity to be introduced, while performing real time (dynamic) feedback from 

measurements, as well as joint (on-line) parameter estimation - optimization and 

stochastic optimization. Subject to constraints and a specified reliability of meeting water 

quality requirements for a current period, the method minimizes the expected value of the 
10

cost in the next (remaining) periods. A comparison between (adaptive) deterministic 

feedback control and the stochastic control formulated by [37] showed a clear cost 

reduction using the stochastic control formulation, with increasing difference as the 

uncertainty increases. Despite the accommodation of more complexity, and more general 

constraints, dynamic control methods that rely on PDE models are not yet suitable for 

complex real world problems. 

One of the important insights that emerged in this implementation of stochastic 

control is the “probing” and “caution” effects highlighted by Bar Shalom [8]; the effect of 

the stochastic/perturbation part in the dual-control example [of Lee and Kitanidis] is that 

of sensitivity analysis and system excitation (the “probing” effect) followed by 

measurements and gaining information about system parameters that resulted in a 

substantial improvement. A paradigm shift is embedded here: rather than focusing on 

general predictive power (or lack of it), the dynamic control approach anticipates how the 

actual (future) state will deviate from estimated state currently in hand, and steers the 

system to mitigate possible losses (the “caution” effect). These two effects (of probing 

and anticipation/caution) imply yet another effect – that of goal-oriented learning. 

The advantage of dynamic control was demonstrated by [16] who used differential 

dynamic programming to determine the benefits of time-varying optimal groundwater 

pumping policies, with the goal to reduce groundwater concentrations (of a contaminant) 

to acceptable levels. They demonstrated that static pumping policies would cost 45-75% 

more than policies that allow time-varying pumping rates, where the management model 

can “chase” the contaminant plume. Another set of developments along this line [17-18, 

74] made use of the “transition function” (TF) that models (or transforms) the system 

from one state to the next (in the groundwater contamination case, the TF consists of the 

matrices generated by the finite element model at each time step) in order to reduce the 

number of iterations needed for convergence and overall computational time in the 

differential dynamic programming. 

A substantial use of the second derivatives of the transition function in a constrained 

differential dynamic programming (DDP in a complete form) was made [74] with respect 

to a general case pump & treat remediation, including pumping scheduling and finding 

best well location. In this work [74], these derivatives were used to generate feedback 

laws with the aid of the penalty function method (which converts the constrained optimal 

control problem to unconstrained optimization, and consequently, allows flexibility in the 

response of the feedback laws to violation of constraints). These feedback laws describe 

relationships between required corrections of the control variables and weighted 

deviations of observed states from the predicted states. The goal was to find the 

relationships between the second derivatives of the transition function and evolutionary 

feedback laws, where the latter relate deviations from (and hence, required corrections to) 

optimal pumping scheduling and deviations of heads and concentrations (state variables) 

from their anticipated states, through weights discovered/assigned to these state 

deviations. The methods requires, as a first step, to employ a (deterministic) model and 

initial “optimal” pumping policy, which enables to build the first transition function, and 

find relationships between control and state deviations. The feedback laws are obtained 

by adjusting the relative weight assigned to each penalty function (corresponding to each 

control variable). 
11

If we disregard the evolutionary nature of the feedback laws, the simple linear 

relationships expressed by the feedback laws (between observed deviation and required 

action) resembles the inverse of action-response functions used in different works [39-

40]. It is interesting to note that while the transition function is derived from the 

governing PDE (flow and transport) model (which could be viewed as an elaborated 

response function model), the feedback law represents cause-effect rules (much like the 

inverse of the transition function) that compensate for model errors, regardless of the 

source of the errors. It is also interesting to note that the evolution of the feedback laws 

over time has an element of memory and learning (from past cause-effect relationships). 

Results from a simplistic example [74] showed to be robust and efficient in terms of 

reducing cost (by 4-51% less than optimization without using a feedback law) as well as 

required computer time, for up to 25% deviations from mean parameter values (i.e., 

uncertainty up to CV = 0.25). 

Although exercised with only small perturbations (hence, small uncertainty) and 

some other limitations, this particular (complete) DDP approach is the first 

control/optimization method that frees itself not only from the need in a rigorous, well 

defined statistical/uncertainty model (with assumed PDF, correlation structure, etc.) but 

also free from both parameter errors and model errors, yet without neglecting uncertainty, 

and indirectly, reducing it, which makes this work a milestone that calls for continuation. 

Other works have coupled optimization with network design (optimal monitoring and 

information extraction from new wells) [7, 31, 40-42, 68], where the former [7] coupled 

sequential development of the groundwater withdrawal management with sampling 

strategies, dynamically, which led to the solution of the withdrawal design using a 

closed-loop stochastic control (dual control) method that includes anticipation of future 

observation locations; the decomposition of the cost function into deterministic and 

stochastic parts, particularly, the inclusion of uncertainty in the cost function leads to 

trade-off between cost of new wells and uncertainty reduction. The sampling network 

design method sequentially selects new measurement locations based on the combined 

effect of the state variable (hydraulic head) uncertainty at that location, and the sensitivity 

of the cost function to that uncertainty. More specifically, new sampling locations are 

selected using the Bayesian approach (to condition new measurements on existing 

information) and based on the product of the sensitivity of the stochastic part of the cost 

function and the modeled (predicted) variance of the state-variable (hydraulic head) at 

that location; that is, the sensitivity of the cost function to the head uncertainty is 

weighted by the magnitude of the prediction error – and vice versa (the prediction error is 

weighted by the sensitivity of the cost function to this error). The head uncertainty is 

evaluated by first-order, second-moment groundwater flow model, where the head 

uncertainty is linked to uncertainty in hydraulic conductivity, boundary conditions, 

recharge, and leakage (all are inputs of the PDE). 

3. Interim conclusions 

The theoretical developments and adaptations of methods from the different disciplines 

of operations research, stochastic control theories, and artificial-intelligence/softcomputing for management of oil reservoirs and groundwater remediation have provided 

insight into 
12

a) the effect of uncertainty (even if just in one parameter) on optimal management and 

cost; 

b) the inseparability of the various components of optimal reservoir management, such 

as optimal scheduling and best new well location for either pumping/injection or new 

monitoring wells; 

c) the inseparability between optimal management and characterization; 

d) the relationships between parameter uncertainty, reliability, and risk; 

e) the relationships between parameter uncertainty and cost; 

f) the effect of probing the system, system anticipation, and the “caution” that follows; 

g) the similarity between the components of sensitivity analyses, random perturbations, 

and response functions and their “inverse” - weighted feedback laws; 

h) the ability to compensate for unknown model errors by determining appropriate 

weighted feedback policies, particularly under dynamic feedback control; 

i) the hidden forms of memory and learning that exist in some statistical models 

(particularly Bayesian statistics), particularly where recursive/evolutionary information 

processing takes place, as is the case in some dynamic control systems, and particularly 

where such processing results in corresponding feedback; 

j) the strength of Bayesian approaches in both estimation and uncertainty reduction. 

The advantage of the control approach is in shifting the emphasis from one type of 

intelligence – that of predictions of first principle (physically-based) models to goaloriented system anticipation (the anticipation of the effect that a control action would 

have on the goal, i.e., on the cost function), as well as shifting sensitivity analysis (of 

general model predictions) to sensitivity of the cost function (to parameter uncertainty 

and particularly, to state uncertainty), which changes the experimental design and overall 

planning. This goal-oriented intelligence is less “ambitious” than the “know-it-all” firstprinciple model. Our goal is to increase the intelligence of the goal-oriented anticipating 

model by combining/integrating knowledge and models from all disciplines in a 

multiresolutional decision support system (MR-DSS or MRDS), e.g., [4-5, 43-48]. 

4. Increasing intelligence with intelligent control 

Fortunately, the area of intelligent control, particularly, the MRDS has been 

developing rapidly during the last two decades, combining the advantages and eliminating 

the limitations of control theories, operations research, and artificial intelligence. For 

example, an intelligent control agent such as MRDS could free the dynamic control from 

its ultimate dependence on the rigid PDE, and can increase its learning, accumulated 

memory, and speed of convergence to optimal solutions by orders of magnitude. 

Moreover, one of the appealing outcomes of the stochastic approach (including stochastic 

PDE) – the effect of conditioning on uncertainty reduction via correlations among 

variables – could be amplified significantly by extending the associations among 

variables on all relevant scales (through advanced MR clustering methods) far beyond 

linear the statistical correlation used in the traditional stochastic approach; the MultiResolutional (MR) knowledge representation in MRDS maximizes the information 

hidden in interdependencies among these variables on all levels of resolution, independent 

of any particular single-scale model. By maximizing extraction of information, the MR 

approach effectively reduces uncertainty and overcomes the problem of lacking and 
13

corrupted information. Most importantly, by using intelligent control, specifically, a goaloriented MR knowledge representation, we could eliminate the dependency on PDE 

models, and use them just as interpretations and general gap-filler in the process of MR 

rule building (the latter being based on experiences and cause-effect relationships). An 

adaptive MR knowledge representation is the only way to integrate all the methods from 

all disciplines – to benefit from the advantages of the different models and eliminate their 

limitations (particularly their rigid structure); to break through the rigid serial, modelbuilding process (currently done in segregation and isolation) and (hence) to enable more 

powerful use of data and knowledge from all disciplines; to provide the highest 

uncertainty reduction possible, and efficient global stochastic optimal control of complex 

natural resources systems such as oil reservoirs and groundwater, with the highest 

intelligence and autonomy possible for particular goals. 

 However, we are still facing the challenge of performing and defining optimal 

integration between PDE models and multiresolutional representations, and since such 

integration depends on model quality and data quantity and quality, this is an adaptive 

integration process as well. One criterion for such “optimal” integration would be 

uncertainty reduction (resulting from the integrated MR system), which brings up yet 

another challenge: to define the metrics for uncertainty reduction. 

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AGENT WITH REASONING AND LEARNING. THE STRUCTURE DESIGN 

Dr. Leonid M. Polyakov 

Globe Institute of Technology 

New York, NY 

Leonid@globeinstitute.org

ABSTRACT 

Reasoning and learning are the most powerful 

intellectual functions. It is not easy to emulate 

them. Main problem is determined by nature of 

reasoning that is based on computation with 

words instead of computation with numbers. 

There are a lot of different approaches to the 

knowledge representation in the agent’s 

knowledge base. The most important languages 

of knowledge representation are preposition 

logic and predicate logic. Design of the agent 

models of intentional (conscious) and 

unintentional (unconscious) reasoning 

(intuition) with multi-knowledge base structure 

based on preposition and predicate logic, 

learning and heuristic generation are topics of 

this discussion. 

Keywords: agent, design, learning, reasoning, 

preposition logic, predicate logic, knowledge 

base, rules of reasoning, application rule, 

hypothesis, intuition, multi-KB system. 

APPROACH TO THE PROBLEM 

SOLUTION 

Reasoning, as we know, is the process of 

drawing conclusion from facts. There is a lot of 

research dedicated to the problems of reasoning 

and the agent structure design [1,2,4,6]. All of 

them are based on representation of knowledge 

as rule-based, semantic net or frame structure 

knowledge base. These knowledge bases (KB) 

include just knowledge of application (AKB) 

(domain oriented KB). Rules of reasoning are 

applied on AKB in different ways for different 

agents. The theorem prover is the representative 

of the system with reasoning but it is design 

without of the KB. Most of the existing systems 

with reasoning are not universal theorem prover 

(http://wwwformal.stanford.edu/clt/ARS/Entries/acl2). These 

systems are based on rules of reasoning and 

don’t work with application knowledge ether. 

Some of them, like ACL2, are designed as multiKB systems. However, all these systems are 

based just on preposition logic. The most 

interesting result in the area of reasoning is the 

Jess language (Jess, the Java Expert System 

Shell, http://herzberg.ca.sandia.gov/jess/ 

demo.html). This system is not the multi-KB 

system and has just one KB-AKB. Information is 

presented by predicate logic. Rules of reasoning 

are incorporated into source code. Idea of a 

multi-KB in search engines also was described 

by Dr. Lotfi Zadeh in “The Prototype-Centered 

Approach to Adding Deduction Capability to 

Search Engines- The Concept of Protoform” 

(BISC letter, 21 Dec 2001) 

http://www.cs.berkeley.edu/People/Faculty/Hom

epages/zadeh.html In this letter: “The deduction 

database is assumed to consist of logical 

database and a computational database, with the 

rules of deduction...” 

Multi-KB structure is only the possible way to 

increase level of universality of the agent up to 

the level of AI system [5]. Separation of AKB 

and RKB from the program converts a 

conventional system into system with ability to 

learn, creates conditions for teaching the system 

through delivery new rules of application by an 

expert in area of application and reasoning 

without knowledge of programming. It is 

important step from a conventional system to the 

AI system. New rules should have the same 

structure as existing rules. New processes can be 

added as new program modules. Multi-KB 

structure creates conditions to design a system 

with ability to generate rules as possible 

hypothesis in the AKB (Fig.8). The first KB is 

application knowledge base-AKB; the second 

one is a reasoning KB-RKB. RKB has rules of 

reasoning. RKB is universal KB. It can be used 

with different AKB. The number of areas of 

application or number of Goals determines the 

number of AKB. The Double-KB structure of a 

system is shown on Fig.1. The process of 

reasoning is shown on Fig. 2. Complicated 

application rules should be decomposed to 

simple structure by rules of reasoning (AndElimination rule-RR on Fig.2) application. 

Process of reasoning in preposition logic is 

determined by terms of application rules (AR). 

Process of reasoning in predicate logic is 

determined by predicate of application rules 

(AR). Choice of rules of reasoning (RR) is 

determined by the structure of the application 

rule. New knowledge is generated by application 

rules to the World Model (WM). Technically a 
process of reasoning can be described as the 

chain of steps: 

Data-AR activation-AR application to the 

WM (testing all chains of related knowledge)-

RR activation 

Fig. 3 shows four-steps algorithm. Fig.4 shows 

Forward-chain algorithm of reasoning that is 

based on rules RR15-RR17. Application of the 

rules RR1-RR14 is not shown. Fig.6 presents 

realization of multi-KB structure in the systems 

with preposition and predicate logic. Fig.7 

presents realization of multi-KB structure in the 

systems with INTUITION. Definition and nature 

of intuition is described in [5]. Discover of the 

Dr. Ben Seymour (neuroscientist from London 

University College 

(http://news.bbc.co.uk/go/pr/fr/-

/2/hi/health/3791357.stm) supports this 

hypothesis. 

 RKB AKB 

 

 System 

Fig. 1 The double-KB system structure

 PREPOSITION AND PREDICATE LOGIC RULES OF REASONING 

There is limited set of reasoning rules in preposition logic [1-5]: 

RR1. Implication Elimination: α ⇒ β, (modus ponens-mp) (IF α is in DB THEN β⇒true) 

RR2. And –Elimination: α1∧α2∧α3∧αn ⇒ LIST(αi), LIST(αi) = α1,α2,α3,... αn 

 con(αi) ⇒ LIST(αi), [i=1,n] 

RR3. And-Introduction: α1 ,α2 ,α3,... ,αn ⇒ α1 ∧α2 ∧α3...∧αn 

 LIST(αi) ⇒ con(αi), [i=1,n] 

RR4. Or-Introduction: LIST(αi)⇒ α1∨α2∨α3∨...∨αn αi = α1 ,α2 ,α3,... ,αn

 LIST(αi) ⇒ dis(αi), [i=1,n] 

RR5. Double-Negation Elimination: ¬ ¬ α ⇒ α

RR6. Unit Resolution: α ∨ β ∧ ¬ β ⇒ α

RR7. Resolution: α ∨ β ∧ β ∨ γ ⇒ α∨ γ

RR8. Universal Elimination: ∀ν α(ν) ⇒ α(g), (from DB: ν = g) 

RR9. Existential Elimination: ∃ ν α(ν) ⇒ α(g) (from DB: ν = g) 

RR10..Existential Introduction: α(g) ⇒ ∃ ν α(ν) (from DB: ν = g) 

RR11. DeMorgan Laws 

RR12 Universal Generalization: (∀x) P(x) 

RR13 Existential Generalization: (∃ x) P(x) 

RR14 Rules of induction: P(1)=T 

 (∀k) {[P(k)=T]⇒ [P(k+1)=T]} P(n) ⇒ T 

RR15 Associative law 

Reasoning 

Knowledge base

(Rules of reasoning)

Internal data 

representation 

Inference engine

Interface

Variables description 

Environm

Translator

Application 

Knowledge base

(Application rules)

Goals 
This set of rules creates the universal RKB. 

Example of the process of reasoning. 

Suppose, DB initially includes facts A, B, C, D, and E, and AKB contains application rules: 

AR1: IF Y is true AR3 

 AND S is true AR3 

 

 AND D is true AR2 

 THEN Z is true 

 

AR2: IF X is true AR1 

 AND B is true 

 AND E is true AR4 

 THEN Y is true RR 

 

AR3: IF A is true 

 THEN X is true 

 

AR4: IF P is true RR: IF S and B and W is true THEN S is true 

 THEN S ∧ B ∧ W is true 

 

 Fig. 2 An inference (forward) chain in a system based on proposition logic.

For proposition logic Forward chaining (data-driven reasoning) 

 DB DB DB DB 

 IDP(WM) 

 IDR (WM) IDR (WM) IDR(WM)

 AKB AKB AKB AKB 

 Goal

 RKB RKB RKB RKB

Fig.3 The system structure and algorithm. IDR-internal data representation, WM-World Model, AKBapplication knowledge base, DB-Data base (external data representation), RKB-reasoning knowledge 

base 

ABCDE X

 Y&D&S→Z 

X&B&E →Y 

 A→X 

 C → P 

 S&B&W← P 

 L&M→N 

 Y&D&S→Z 

X&B&E →Y 

 A→X 

 C→ P

S&B&W← P

 L&M→N

 S,B,W X P 

 A B C D E 

 Y&D&S→Z 

X&B&E →Y

 A→X 

 C→ P

S&B&W← P

 L&M→N

A B C D E 

S,B,W XPY

 Y&D&S→Z 

X&B&E →Y

 A→X 

 C→ P

S&B&W← P

 L&M→N 

con(αi)⇒LIST(αi)

 ............. 

α∨β∧¬β⇒ α

con(αi)⇒LIST(αi)

 ............. 

α∨β∧¬β⇒ α

con(αi)⇒LIST(αi)

 ............. 

α∨β∧¬β⇒ α

con(αi)⇒LIST(αi)

 ............. 

α∨β∧¬β⇒ α

Y 

D Z 

S 

A X 

B 

E 

S and B and W 

P 

ABCD E ABCD E ABCD E

ABCDE XP

ABCD E
SYSTEMS ARE BASED ON PREDICATE LOGIC 

Syntax in predicate logic can be presented as: PREDICATE (LIST OF TERMS - OBJECTS) 

PREDICATES: RELATIONSHIP, PROPERTIES, and FUNCTIONS. 

 Suppose, the following facts in the predicate Logic using meaningful predicates and functions rules. 

Rules of application 

1) Anyone sane does not teach an AI course. 

 ∀x sane(x)→¬ AIInsructor (x) ) 

2) Every circus elephant is a genius. 

 ∀xCircusElephant(x) → genius(x) 

3) Nothing is both male and a circus elephant. 

 ¬ ∀x Male(x) ⇔ CircusElephant(x) 

4) Anything not male is female. 

 ¬∀x Male(x) ⇔ Female(x) 

Data 

1) Clyde is not an AI instructor. ¬AIInsructor(Clyde) 

 5) Clyde is a circus elephant. CircusElephant(Clyde) 

Determine state of the following is true, false or cannot be determined based on the application rules: 

 Clyde is a genius. 

 

Rules of reasoning include all rules of reasoning based on preposition logic and set of rules that are specific 

to the predicate logic: 

RR16. Find all atomic sentences that related to the first term in DB 

RR17. Find all atomic sentences with conclusion that related to the predicate 

 of the result of RR1 action 

RR18. Check each of them against solution question. 

ALGORITHM OF REASONING

 Proof that Clyde is a genius: DB 

 RR16 RR16 

 AKB 

 ¬AIInsructor(Clyde) CircusElephant(Clyde) 

 RR17 

 RR17 

 ∀x sane(x)→¬ AIInsructor (x) ∀xCircusElephant(x) → genius(x) 

 

 ¬ ∀x Male(x) ⇔ CircusElephant(x) 

 RR18 

 No 

 RESULT Yes 

 RR17

Fig.4 shows Forward-chain algorithm of reasoning based on rules RR15-RR17. Action of the RR1-RR14 is 

not shown. 

x → Clyde

Genius(Clyde)

Male(Clyde)
 Fig.5 “Wumpus World” model (preposition logic). 
Fig. 6. This system (predicate logic language) is based on the algorithm presented by Fig, 4 
Fig 7. Modeling of INTUITION. 
Fig 8. Hyphotheses generator. First 5 expressions are basic knowledge in math, rest of the expressions are 

 generated as the heuristics to mach to the presented set of numbers. Analyzer shows correct 

 expression. This system has a very limited basic math knowledge.. 

 

 

 

 

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 [5] Polyakov L. Structure Approach to the Intelligent System Design. Proceedings of the 2002 

 PerMIS Workshop August 13-15, 2002. 

 [6] Russell S. Norvig P. Artificial Intelligence. A Modern Approach. Prentice Hall, 1995 
Miniaturized all-solid-state 3D camera for real-time range imaging

Thierry Oggier∗, Peter Seitz and Nicolas Blanc 

CSEM SA, Swiss Center for Electronics and Microtechnology, Badenerstrasse 569 

 CH 8048 Zurich, Switzerland 

ABSTRACT 

The perception of the world in three-dimensions is natural for 

human beings. Technical 3D imaging systems, however, have 

suffered until today from high complexity and severe practical 

limitations to obtain 3D-information of the environment. This is 

overcome by a new type of optical 3D camera based on the timeof-flight (TOF) principle: Light from an LED or laser diode array 

is RF modulated at a few tens of MHz and illuminates a scene. The 

light is diffusely reflected back by the objects in the scene, and it is 

imaged with a conventional lens onto a custom solid-state image 

sensor. Each of its pixels is capable of synchronous demodulation 

of the incident modulated light, for the precise local determination 

of the parameters offset, amplitude and phase. The phase 

information is a direct measure of the local distance. 

This principle has been employed in a miniaturized 3D camera 

(SwissRanger) for the acquisition of range images in video realtime. Without any mechanical scanning parts and with eye-safe 

emitting power, the camera delivers distance data, intensity 

information as well as an estimation of the distance accuracy for 

each of its 124x160 pixels. 

Due to the use of a combination of CCD principles and CMOS 

circuitry in each pixel, a distance resolution is obtained that is 

close to the physical noise limitations given by the photon shot 

noise. Under optimum conditions a distance resolution of a few 

mm over a measurement range of several meters is obtained. A 

large number of applications are envisaged for which our TOF 

range camera provides a cost-effective and simple solution. 

Keywords: Optical 3D imaging, range finder, SwissRanger, 

distance measurement, lock-in pixel, time-of-flight, range camera. 

1. INTRODUCTION 

We live in a three-dimensional world. Human beings 

are able to perceive their environment thanks to the “human 

stereo vision” system, the eyes. Several technical 

approaches are known to render imaging systems more 

intelligent by letting conventional cameras obtain 

information about the third dimension. Methods based on 

the triangulation principle were developed in the past e.g. 

stereo vision systems or systems based on structured 

projection. So far, the required computational cost 

underlying such a triangulation system and the inherent 

need of a minimum base distance of the two sensors (the 

projection and sensing unit) prevented their introduction 

into markets that are demanding low cost and small camera 

size. Another approach based on interferometry achieves 

very high distance resolutions, but due to its short 

measurement range, interferometers are only employed in a 

very restricted number of applications. Very promising 

results are achieved with time-of-flight (TOF) measuring 

devices. Resolutions in the sub-centimeter range and 

measurement ranges of several hundred meters have been 

reported. The drawback of these TOF-systems lies mainly in 

the high emitted power that is required and the necessity to 

use moving mechanical parts (e.g. scanners), leading to 

system costs that are unacceptable for many applications. 

Until recently, no reliable and cost-effective 3D 

imaging cameras have been available on the market. The 

optical 3D camera described in this work was developed 

targeting a new, cost-effective imaging system allowing to 

capture three-dimensional imagery of the world in video 

real-time. A cost-effective and robust camera dictates the 

use of an all-solid-state, application-specific image sensor 

obviating the need for any moving parts. Extensive 

optoelectronic characterization results prove that the 

achieved distance accuracies approach the ultimate 

resolution given by the photon shot noise [1]. 

In the first section of this work, the principle of optical 

distance-measuring cameras based on the TOF method is 

explained. An electromagnetic wave, modulated at a few 

tens of MHz is emitted by the camera’s illumination unit, 

illuminating the entire scene. The light, diffusely reflected 

by the different objects in the scene, is imaged onto the 

camera’s custom sensor by a conventional lens. Within each 

pixel of this sensor, the signal is demodulated 

synchronously. The local phase shift - caused by the imaged 

object’s distance - as well as the intensity and the amplitude 

of the incoming electro-magnetic wave are obtained at each 

pixel site. 

In the following section, the working principle and the 

requirements of the sampling process in the so-called “lock-
in pixel” [2] and the sensor are discussed. Extensive

optoelectronic characterization results corroborate the 

theoretical predictions, proving that the SwissRanger 

camera yields distance data whose precision is close to the

photon quantum noise limit. 

In the fourth section different possible applications are

described, in which the knowledge of the third dimension

makes it possible to work with straightforward, simple 

algorithms. Some pictorial results of these algorithms

illustrate the effectiveness of the chose approach based on 

range image data. The market potential of such costeffective 3D-imaging devices in their different application 

fields is discussed and illustrated.

Finally an outlook for future improvements in the field 

of optical 3D cameras is given and their implications on the

camera’s performance is briefly discussed. 

2. TOF MEASUREMENT PRINCIPLE 

The TOF measurement principle is based on the finite

speed of light c ≅ 3•108

 ms-1 (in air). In order to reduce the

required timing constraints on the system, instead of a pure 

pulse TOF measurement, a homodyne phase shift

measurement is performed, as illustrated in Figure 1.

The principle is based on an illumination unit, which emits

an intensity-modulated electromagnetic wave front. This

emission signals can be described as 

e(t) = e ⋅[ ] 1+ sin( ) 2πf ⋅t (1)

e: Emitted mean optical power 

f: Modulation frequency 

After reflection on the objects in the scene, the wave

front reaches the sensor again. The power impinging on the

sensor is reduced by different target characteristics 

(reflectivity, distance) and optical properties of the camera. 

The total signal attenuation can be summarized as a factor k. 

In addition to the modulated light, background light BG e.g. 

sun light or artificial light is sensed. Compared to the high 

frequency of the modulated signal, the background 

illumination can be considered as being constant. Therefore, 

the signal power impinging on a pixel can be described as

s(t) = BG + e ⋅ k ⋅[ ] 1+ sin( ) 2πf ⋅t −φ (2)

BG: Background illumination power 

k: Attenuation factor 

φ: Phase delay arising from the object’s distance

By sampling the incoming signal four times within a

modulation period, the incident signal’s modulation 

parameters can be completely determined, by making use of

Equ. (3), (4), and (5). This calculation procedure is known

as the four-bucket algorithm [3]. The four sampled and 

accumulated photo charge signals are denoted as A0, A1, A2

and A3. 

Figure 1: Measurement principle of the optical TOF 3D range camera. High-frequency modulated light is emitted by an LED array, it

is reflected diffusely by the object, and it is demodulated synchronously in a lock-in image sensor. 
















−

− =

0 2

3 1

A A

A A

φ atan (3)

4

A A A A B 0 + 1 + 2 + 3 = (4) 

[ ] [ ]

2

A A A A 2

0 2

2

3 − 1 + − A = (5) 

φ: Measured phase delay 

B: Measured offset 

A: Measured amplitude 

An illustration of the sampling process is sketched in 

figure 2. The phase φ represents a direct measure of the

acquired target distance, B corresponds to a conventional

black and white intensity image and A is the amplitude of

the incoming wave. 

Figure 2: Illustration of the four samplings of the wave A0, A1, 

A2 and A3 and the reconstituted wave characteristics 

amplitude A, intensity B and phase φ. 

The distance can be derived from the phase according 

to 

φ

π = ⋅ 2

L0 L (6)

L0: Non-ambiguity range 

L0 represents the non-ambiguity range of the phase 

measurement and corresponds to half the wavelength of the 

modulation frequency (7). 

f

c L

2 0 = (7)

A more detailed discussion of homodyne phase

measurement and its physical detection limit given by the 

photon shot noise is given in [4].

3. SWISSRANGER CAMERA 

DEMONSTRATOR 

Figure 1 illustrates the different components required 

for the distance-measuring device. The camera consists of: 

• Illumination unit 

• Optical elements for imaging and filtering

• Custom sensor 

• Sensor control electronics 

• Data processing electronics 

• Camera interface 

Based on the described synchronous demodulation 

image sensor and the optical TOF range imaging principle, a 

miniaturized camera demonstrator (SwissRanger) was 

developed, shown in Fig. 3. Apart from the custom-made 

sensor, the SwissRanger camera only consists of 

commercially available components. 

Its dimensions are 135 mm x 45 mm x 32 mm and the

camera weighs less than 200 g, of which more than half is

the weight of the metal case. The camera offers a lateral 

resolution of 160 x 124 pixels and during operation it

consumes about 1.5 A at 12 V, depending on the particular 

measurement settings. Due to the use of a solid-state image 

sensor and the commercial availability of all other 

microelectronic components, the camera’s measurement

principle is well suited for the fabrication of cost-effective 

products. 

The illumination unit emits an intensity-modulated light 

wave of a few 10 MHz into the entire field-of-view (FOV).

The total emitted mean power amounts to up to 800 mW.

LEDs emitting at a wavelength of 870 nm are employed. In 

general, laser diodes or LEDs can be used in the 

illumination unit. In any case, the maximal optical power 

limit is given by eye safety considerations. Implementing

diffusive micro-optical elements in front of the emitting 

diodes eases on the one hand the eye safety limitations and 

on the other hand illuminates the FOV in a more controlled 

manner.
Figure 3: Photograph of the SwissRanger camera demonstrator. 

The optical elements consist of the imaging optics in 

front of a bandpass filter. The imaging optics forms an 

image of the scene in the sensor plane, and the filter reduces 

possible background illumination in the scene. The imaging

optics has to be adjusted carefully to the illumination unit

and the sensor. Ideally, the illumination unit only emits light

in the FOV determined by the optics and the sensor. The 

filter also needs to be designed according to the light source. 

LEDs require a broader bandpass filter than laser diodes. 

Therefore, for outdoor applications laser diodes allowing the 

implementation of a more narrow bandpass filter are 

preferred to LEDs. 

Figure 4: Electronics board of the SwissRanger camera 

demonstrator. 

The electronics board provides the different signals to

control the sensor. These signals are required for the 

readout, supply voltages or gate controls. The analog to

digital conversion is performed on the printed circuit board,

as well as the entire data processing, implementing the 

equations (3), (4) and (5). The camera settings allow the

definition of a noise-level threshold to withhold inaccurate 

distance measurements from being made available outside 

the camera. The interface to the computer conforms to the 

widely used USB2.0 standard. Different parameters such as 

integration time, definition of region-of-interest (ROI) or

spatial filtering can be programmed by the user through the 

USB2.0 interface. 

4. 3D LOCK-IN IMAGE SENSOR

The application-specific image sensor has been

designed, simulated and manufactured in a 0.8 μm 

CMOS/CCD technology from the silicon foundry ZMD in

Dresden, Germany. The sensor contains 160 x 124 pixels.

Each pixel can be addressed and read out individually, thus, 

any arbitrary ROI can be defined. The sensor is based on the 

so-called 2-tap pixel architecture, implying that each pixel 

contains two photocharge storage sites. This architecture 

represents a trade-off between speed (4-tap) and sensitivity 

(1-tap). A more detailed comparison about the different

multi-tap pixel architectures is reported in [5].

Figure 5: Picture of the SwissRanger sensor manufactured on a

0.8 μm CMOS/CCD technology. 

The pixel has been created using ISE-TCAD simulation 

tools. The CCD-gates within each pixel allow fast

photocharge separation, temporal sampling and

accumulation. More details about CCD imaging have been

published in [6] and [7]. Because of the high modulation

frequencies and the requirements in TOF-systems regarding 

the shutter, dominating the demodulation characteristics, it

is of highest importance to transfer and sum the 

photocharges with as little additional noise as possible. For

this reason, we employ the CCD principle, realized with a 

buried channel CCD option in an otherwise standard CMOS

process for virtually noise-free photocharge separation,

sampling and accumulation. The same CMOS technology is 

used to address and read out the pixels. 

This combination of CMOS and CCD technology does

not only result in a pixel performance that is optimized for

optical TOF range imaging, it also opens the way to future 
system-on-chip (SoC) solutions of cost-effective single-chip

TOF range cameras. 

Extensive optoelectronic characterization confirms that 

the SwissRanger camera demonstrator approaches the

physical detection limit given by the photon shot noise. 

Under favorable measurement conditions (little background

illumination and pixel signals close to saturation) a distance 

resolution of a few mm can be obtained for a measurement 

range of several meters [1].

5. APPLICATION EXAMPLE 

Thanks to the advantageous properties of the

SwissRanger camera (high distance resolution of TOFmeasurements, high lateral resolution and speed) completely

new solutions to difficult measurement problems can be

envisaged. A large number of applications fields can be

covered in a more cost-efficient way.

In this paragraph, we describe a few application

examples of optical 3D range cameras based on the TOF 

principle. Typical pictures illustrate the feasibility of the 3D

imaging approach for these problems. 

Figure 6 shows three views of one 3D picture of a

human face taken by a SwissRanger camera. 

Figure 6: Shot of the SwissRanger camera on a human face. 

The 3D picture was taken with an exposure time of less 

than one second. The black-and-white reflectivity 

information is projected onto the measured threedimensional surface. This results implies that optical 3D

imaging can provide valuable additional information to the 

reflectivity map of a human face, without any special 

requirements, in a short time and at low cost. It seems 

obvious that biometrical applications could make good use

of this additional information for increased security. 

Another application example is motion tracking. The

knowledge of the third dimension allows implementing 

much faster and easier detection algorithms. Figure 7 shows 

the hand tracking of a person in a room. Three pictures of a 

video-rate sequence are presented. 

Figure 7: 1st row: b/w coded distance map. 2nd row: b/w 

reflectance image. 3rd row: hand tracking. 

In the first row of figure 7, the distance map is intensity 

coded. Pixels considered not accurate enough for the hand 

tracking are withheld by the camera at pixel level. These 

pixels are represented in the first and second row as black 

pixels. Pixels in the first image row represent the measured

distance. Dark pixels correspond to closer distance whereas 

bright pixels originate from objects farther away from the 

camera. The second row shows the conventional b/w

reflectance images of the sequence. The third row shows

those pixels in white that are extracted by a simple handtracking algorithm.

Information about the third dimension makes it much

easier to develop fast, reliable algorithms of low 

complexity, for which the presented hand tracking is a good 

example: Algorithms based on the distance maps save a lot 

of computational power compared to pure 2D algorithms. 

Figure 8 shows a sequence of range images of a scene, 

acquired at video-rate. The distance on the different maps is
b/w coded. Objects with darker pixels are closer to the

camera; brighter objects are situated farther from the 

camera. For illustration, the used colour-coded distance

scale is provided. The sequence shows a person entering a

room. This person can easily be tracked and detected by

processing the distance information. Any possible 

influences by lighting effects, such as shadows, do not

influence the distance map, in strong contrast to the 

detection algorithms based on conventional 2D-sensors. 

Figure 8: Sequence of distance maps acquired by the SR-2 

camera for room observation.

6. OUTLOOK 

The next generation of 3D-TOF cameras will be based

on CMOS/CCD technologies with smaller feature sizes. 

This will increase the number of lock-in pixels and their 

density on one custom TOF image sensor. By using laser

diodes and vertical cavity surface emitting lasers (VCSEL), 

outdoor applications are targeted, first at closer distances

and then at distances of several tens of meters. New pixel

architectures and technologies will allow higher modulation 

frequencies [8] and thus further improve the distance

resolution. Finally, the use of microlenses is foreseen in

order to increase the pixel sensitivity. 

7. SUMMARY AND CONCLUSIONS 

In this paper, an overview of the optical homodyne

phase measurement technique used for distance

measurements is given. The TOF-principle as implemented 

in the SwissRanger camera demonstrator is presented and 

the different required components are described.

The potential of the optical 3D TOF imaging principle 

is illustrated with three examples, face recognition, hand 

tracking and room observation, requiring only straightforward and simple algorithms. Many more applications are 

foreseen in a wide range of applications, such as

automotive, security, safety, door-and-gate control, robotics,

autonomous vehicles, computer pointing devices, domotics,

games, biometrics, toys, etc. 

It is concluded that the described optical 3D imaging as 

implemented in the SwissRanger camera demonstrator 

represents an outstanding measurement concept for 

acquiring true images of our rich three-dimensional world,

that can finally been acquired at high speed, high resolution,

with miniature camera systems and at low cost. 

ACKNOWLEDGMENT 

The authors would like to thank all the members of the 

Image Sensing Group of CSEM SA for their continuing 

support in the various phases of this research and 

development project. 

REFERENCES 

[1] T. Oggier et al., “An all-solid-state optical range

camera for 3D real-time imaging with sub-centimeter

depth resolution (SwissRanger

TM)”, Proceedings of the

SPIE, Vol. 5249 No. 65, 2003. 

[2] T. Spirig, P. Seitz, O. Vietze, F. Heitger, „The Lock-in 

CCD – Two-Dimensional Detection of Light“, IEEE

journal of quantum electronics, Vol.31, No. 9, 1995. 

[3] K. Creath, “Phase-Measurement Interferometry 

Techniques”, Progress in Optics, Vol. XXVI, E. Wolf 

(Ed.), Elsevier, 1988. 

[4] R. Lange and P. Seitz, “Solid-State Time-of-Flight

Range Camera”, IEEE J. Quantum Electronics, Vol. 37 

(3), 390-397, March 2001. 

[5] W. Boyle and G. Smith, “Charge coupled

semiconductor devices”, Bell Syst. Tech. Jour., Vol. 49,

pp. 587-593, 1970. 
[6] R. Kaufmann et al., “A Time-of-Flight Line Sensor – 

Development and Application“, Proceedings of the 

SPIE, Vol. 5459 No. 24, 2004. 

[7] A. Theuwissen, “Solid-State Imaging with ChargeCoupled Devices”, Kluwer Academic Publishers, 1995. 

[8] B. Büttgen, T. Oggier, R. Kaufmann, P. Seitz, N. Blanc, 

“Demonstration of a novel drift field pixel structure for 

the demodulation of modulated light waves with 

application in three-dimensional image capture”, 

Proceedings of the SPIE, Vol. 5302 No. 2, 2004 

 ∗

 Contact: thierry.oggier@csem.ch 
Obstacle Detection using a TOF Range

Camera for Indoor AGV Navigation

T. Hong, R. Bostelman, and R. Madhavan

Intelligent Systems Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-8230, U.S.A.

Tel: (301) 975-2865 Fax: (301) 990-9688

Email: {tsai.hong,roger.bostelman,raj.madhavan}@nist.gov

ABSTRACT— The performance evaluation of an obstacle

detection and segmentation algorithm for Automated Guided

Vehicle (AGV) navigation in factory-like environments using a

3D real-time range camera is the subject of this paper1. Our

approach has been tested successfully on British safety standard

recommended object sizes and materials placed on the vehicle

path. The segmented (mapped) obstacles are then verified using

absolute measurements obtained using a relatively accurate 2D

scanning laser rangefinder.

Keywords:

Automated Guided Vehicle, 3D range camera, 2D

Laser Rangefinder, Obstacle Detection and Segmentation.

1. INTRODUCTION

Obstacle detection and mapping are crucial for autonomous indoor driving. This is especially true for Automated Guided Vehicle (AGV) navigation in factory-like

environments where safety of personnel and that of the

AGV itself is of utmost importance. This paper describes

the performance of an obstacle detection and segmentation

algorithm using a 3D real-time range camera.

The 3D range image camera is based on the Time-OfFlight (TOF) principle [8] and is capable of simultaneously

producing intensity images and range information of targets

in indoor environments. This range camera is extremely

appealing for obstacle detection in industrial applications

as it will be relatively inexpensive as compared to similar

sensors and can deliver range and intensity images at a rate

of 30 Hz with an active range of 7.5 m.

Since obstacle detection plays a basic function for autonomous driving, there has been much research on many

different types of sensors, such as sonar [11], color/gray

level cameras [2], FLIR (Forward Looking InfraRed) cameras [10], and stereo cameras [9], [1], [12], [6]. Most of the

vision approaches are not applicable to indoor scenes due

1Commercial equipment and materials are identified in this paper in

order to adequately specify certain procedures. Such identification does

not imply recommendation or endorsement by the National Institute

of Standards and Technology, nor does it imply that the materials or

equipment identified are necessarily the best available for the purpose.

to lack of texture in the environment. Other researchers

have proposed LADAR (Laser Detection And Ranging)

sensors for detecting obstacles [4], [3], [5]. However, one

dimension LADAR which has been used in AGV industry

is not suitable for the 3D world of factory environments.

Our proposed approach to obstacle detection uses a low

cost, 3D real-time range camera. First, we calibrate the

camera with respect to the AGV so that we can convert

the range values to 3D point clouds in the AGV coordinate frame. Second, we segment the objects which have

high intensity and whose elevation values are above the

floor of the operating environment on the AGV path. The

segmented 3D points of the obstacles are then projected

and accumulated into the floor surface-plane. The algorithm

utilizes the intensity and 3D structure of range data from the

camera and does not rely on the texture of the environment.

The segmented (mapped) obstacles are verified using absolute measurements obtained using a relatively accurate 2D

scanning laser rangefinder. Our approach has been tested

successfully on British safety standard recommended object

sizes and materials placed on the vehicle path. In this paper,

the AGV remained stationary as the measurements were

collected.

The U.S. American Society of Mechanical Engineers

(ASME) B56.5 standard [13] was recently upgraded2to

allow non-contact safety sensors as opposed to contact

sensors such as bumpers on AGVs. Ideally, the U.S. standard can be upgraded further similar to the British safety

standard requirements [14]. The British safety standard of

industrial driverless trucks/robots requires that (a) sensors

shall operate at least over the full width of the vehicle

and load in every direction of travel, (b) sensors shall

generate a signal enabling the vehicle to be stopped by

the braking system under specified floor condition before

contact between the rigid parts of the vehicle and/or load

and a person, (c) sensors shall detect parts of a persons

body as close as possible to the floor but at least the

2not cited here as the upgrade was not published prior to the date of

this paper.
“test apparatus shall be detected”, (d) the activation of

such sensors shall not cause injury to persons, and (e)

reflective characteristics of test apparatus for personnel

detection means which work without physical contact shall

be representative of human clothing. We anticipate the work

described in this paper and the continuing research efforts

to lay the groundwork towards further upgrade of the U.S.

safety standards for AGVs in factory-like environments.

The paper is structured as follows: Section 2 describes an

obstacle detection and segmentation algorithm using range

camera images. Section 3 provides the experimental results

when the proposed algorithm is employed for detection and

segmentation of British standard test apparatus. Section 4

concludes the paper and indicates future research areas that

are under investigation.

2. OBSTACLE DETECTION AND SEGMENTATION

In this section, we describe an algorithm to detect and

segment obstacles in the path of the AGV using a solidstate Time-Of-Flight (TOF) range camera. The 3D range

camera shown in Figure 1 is a compact, robust and cost

effective solid state device capable of producing 3D images in real-time. The camera has a field-of-view of 42◦

(horizontal) × 46◦(vertical) and is capable of producing

range images of 160×124 pixels. For a brief overview of

the characteristics and operating principles of the camera,

see [8]. Approximately sized British standard test obstacles,

shown in Figure 2, were placed on the travel path.

Fig. 1. The TOF 3D range image camera. The camera simultaneously

generates intensity images and range information of targets in its field-ofview at a rate of 30 Hz with an active range of 7.5 m.

The obstacle detection and segmentation algorithm combines intensity and range images from the range camera

to detect the obstacles and estimate the distance to the

obstacles. The steps of the algorithm are illustrated for a

sample image from the camera:

1) First, a patch data with high intensity values (i.e., the

intensity value is greater than 20) in the front of the

robot are used to fit a plane for estimating the floor

surface as shown in Figure 3(a).

2) Second, the left and right edges of 3D robot paths are

projected to the range and intensity images such that

only obstacles on the path can be considered as shown

in Figure 3(b).

3) Third, all the intensity pixels inside of the left and

right edges are used to hypothesize the potential

(a)

(b)

Fig. 2. Experimental setup. (a) and (b) depict the experimental setups

that are described in this paper. See Section 3 for further details.

obstacle. If the intensity value of the pixel is greater

than half of the average of the intensity in the image

then the pixel is considered as a potential obstacle as

shown in Figure 3(c).

4) Fourth, each potential obstacle pixel in the range

image is used to find the distance to the floor plane

when the distance to the floor is greater than some

threshold as shown in Figure 3(d). The threshold is

dependent on the traversability of the robot.

Potential obstacles in the world model can be accumulated as the AGV drives; Figure 4 shows an obstacle

map representation that is part of the world model. The

obstacles map is shown at 10 cm grid resolution. Nearly

all the obstacles are found, but at the cost of false positives

from the reflected objects. To increase the accuracy of our
(a) (b)

(c) (d)

Fig. 3. Obstacle segmentation algorithm illustration.

obstacle detection, the obstacles in the map and information

obtained from an added color camera may be temporally

integrated. Such integration has proven to be a very useful

cue for obstacle detection [7].

3. EXPERIMENTAL SETUP AND RESULTS

The experiments were conducted under two scenarios as

stated within the British Standard:

1) A test apparatus with a diameter of 200 mm and a

length of 600 mm placed at right angles on the path of the

AGV. The actuating force on this test apparatus shall not

exceed 750 N.

2) A test apparatus with a diameter of 70 mm and a

height of 400 mm set vertically within the path of the AGV.

The actuating force on this test apparatus shall not exceed

250 N.

Figures 2(a) and (b) show the experimental setup for the

two aforementioned scenarios. The center of the camera

lens was centered approximately horizontal and vertical

on the apparatus for all measurements. The scanning laser

rangefinder was offset from the camera by 0 mm vertically,

250 mm horizontally, and to the left of the camera as

viewed from the camera to the test apparatus. The range

camera was used to detect known test apparatus mounted

on a stand and moved to different locations with respect to

the camera.

The obstacle detection and segmentation algorithm was

tested on the British standard test apparatus as described

in [14], and was evaluated against ground truth. A singleline scanning laser rangefinder, shown in Figure 5, mounted

beside the range camera, was used to simultaneously verify

the distance to the test apparatus for each data set and

served as ground truth. The rangefinder produces 401 data
Fig. 4. Obstacle map.

Fig. 5. Experimental setup of the AGV, the scanning laser rangefinder,

and the range camera.

points over a 100◦semi-circular region in front of the robot.

The obstacle detection and segmentation algorithm was

tested on British standard test apparatus which were placed

in 0.5 meter to 7.5 m distances to the sensor. Table 1 shows

the performance of the range camera for measuring the

distance to the test apparatus placed at several distances

from the range camera. As can be seen, the accuracy (mean)

of the range decreases as the distance of the apparatus

placed in front of the range camera is increased.

In Figure 6, the test apparatus was placed at a distance

of 2.5 m from the range camera. Each object in the

test apparatus was clearly detected even though the range

camera was also sensitive to the reflectors on the wall of

the hallway. The resultant intensity, range, and segmented

images are shown in Figures 6(a), (b) and (c), respectively.

The ground truth provided by the scanning laser rangefinder

is shown in Figure 6(d) and has been rotated to show a topdown view.

In Figure 7, the test apparatus is a mannequin leg placed

on the floor with an approximate diameter of 200 mm

and a length of 600 mm. This test apparatus is more

challenging for the algorithm because the entire object is

close to the floor. As can be seen, the legs are detected,

but at the cost of detecting reflectors. Since some reflectors

(see Figure 7(c)) are at a distance of more than 7.5 m,

these are modulated by the non-ambiguity distance range

of the camera. This deficiency can be eliminated by using

two different modulation frequencies (such as 10 MHz and

20 MHz) where the detected objects would be coarsely

represented at a more appropriate distance. The control

algorithm can then intelligently delete them.

4. CONCLUSIONS AND FURTHER WORK

An obstacle detection and segmentation algorithm for

Automated Guided Vehicle (AGV) navigation in factorylike environments using a novel 3D range camera was described in this paper. The range camera is highly attractive

for obstacle detection in industrial applications as it will

be relatively cheap and can deliver range and intensity

images in real-time. The performance of the algorithm was

evaluated by comparing it with ground truth provided by a

single-line scanning laser rangefinder.

We envisage the extension of the work detailed in this

paper in the following areas:

• We believe that the range camera can be used for moving obstacle detection from a moving AGV. The detection

of moving obstacles in the factory floor is a next critical

step for AGV navigation in such dynamic environments.

Additionally, this sensor can be combined with a color

camera for detecting and tracking obstacles over long

distances.

• We also believe that the range camera discussed in

this paper holds good potential to be used in outdoor environments. Towards this, we have taken and analyzed some

outdoor data and the preliminary results show good promise

in using this sensor for outdoor forest environments. Some

prospective applications include mapping factory environments (“lights-out”) manufacturing, and even for use in

space due to its compactness.

5. REFERENCES

[1] P. Batavia and S. Singh. Obstacle Detection Using Adaptive Color

Segmentation and Color Stereo Homography. In Proc. of the IEEE

Intl. Conf. on Robotics and Automation, May 2001.

[2] M. Bertozzi, A. Broggi, A. Fascioli, and P. Lombardi. Artificial

Vision in Road Vehicles. In Proc. of the 28th IEEE Industrial

Electronics Society Annual Conf., 2002.

[3] T. Chang, T-H. Hong, S. Legowik, and M. Abrams. Concealment and

Obstacle Detection for Autonomouos Driving. In Proc. of the Intl.

Association of Science and Technology for Development - Robotics

and Application, 1999.

[4] A. Ewald and V. Willhoeft. Laser Scanners for Obstacle Detection

in Automotive Application. In Proc. of the Intell. Vehicles Symp.,

2000.

[5] J. Hancock, M. Hebert, and C. Thorpe. Laser Intensity-based

Obstacle Detection. In Proc. of the IEEE/RSJ Intl. Conf. on

Intelligent Robots and Systems, 1998.
Table 1

Quantitative Comparison of Performance

Nominal Obst.

Dist. [cm]

3D Range Camera 2D Rangefinder

Mean [cm] Mean [cm]

64 64 65

111 111 111

160 161 161

210 204 210

259 249 259

310 284 310

(a) Intensity Image (b) Range Image

(c) Segmented Image (d) Ground Truth

Fig. 6. Results of the obstacle detection and segmentation algorithm for the experimental setup shown in Figure 2(a). The resultant intensity, range,

and segmented images are shown in (a), (b) and (c), respectively. The ground truth provided by the scanning laser rangefinder is shown in (d) and has

been rotated to show a top-down view.
(a) Intensity Image (b) Range Image

(c) Segmented Image (d) Ground Truth

Fig. 7. Results of the obstacle detection and segmentation algorithm for the experimental setup shown in Figure 2(b). The resultant intensity, range,

and segmented images are shown in (a), (b) and (c), respectively. The ground truth provided by the scanning laser rangefinder is shown in (d) and has

been rotated to show a top-down view.

[6] M. Hariti, Y. Ruichek, and A. Koukam. A Voting Stereo Matching

Method for Real-Time Obstacle Detection. In Proc. of the IEEE Intl.

Conf. on Robotics and Automation, 2003.

[7] T-H. Hong, T. Chang, C. Rasmussen, and M. Shneier. Feature

Detection and Tracking for Mobile Robots Using a Combination

of Ladar and Color Images. In Proc. of the IEEE Intl. Conf. on

Robotics and Automation, May 2002.

[8] T. Oggier, M. Lehmann, R. Kaufmann, M. Schweizer, M. Richter,

P. Metzler, G. Lang, F. Lustenberger, and N. Blanc. An All-solidstate Optical Range Camera for 3D Real-time Imaging with Subcentimeter Depth Resolution. In Proc. of the SPIE Conf. on Optical

System Design, September 2003.

[9] C. Olson, L. Matthies, H. Schoppers, and M. Maimone. Robust

Stereo Ego-motion for Long Distance Navigation. In Proc. of the

IEEE Intl. Conf. on Computer Vision and Pattern Recognition, 2000.

[10] K. Owens and L. Matthies. Passive Night Vision Sensor Comparison

for Unmanned Ground Vehicle Stereo Vision Navigation . In Proc.

of the IEEE Intl. Conf. on Robotics and Automation.

[11] N. Sgouros, G. Papakonstantinous, and P. Tsanakas. Localized

Qualitative Navigation for Indoor Environments. In Proc. of the

IEEE Intl. Conf. on Robotics and Automation, 1996.

[12] R. Williamson and C. Thorpe. A Trinocular Stereo System for

Highway Obstacle Detection. In Proc. of the IEEE Intl. Conf. on

Robotics and Automation, 1999.

[13] American Society of Mechanical Engineers’ Safety Standard for

Guided Industrial Vehicle and Automated Functions of Manned

Industrial Vehicle. Technical Report ASME B56.5, 1993.

[14] British Standard Safety of Industrial Trucks - Driverless Trucks and

their Systems. Technical Report BS EN 1525, 1998.
Performance Evaluation of Temporal Range

Registration for Unmanned Vehicle Navigation

R. Madhavan and E. Messina

Intelligent Systems Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-8230.

Tel: (301) 975-2865 Fax: (301) 990-9688

Email: {raj.madhavan, elena.messina}@nist.gov

ABSTRACT— In this paper, we evaluate the performance

of an iterative registration algorithm for position estimation of

Unmanned Ground Vehicles (UGVs) operating in unstructured

environments. Field data obtained from trials on UGVs traversing

undulating outdoor terrain is used to quantify the performance of

the algorithm in producing continual position estimates. These

estimates are then compared with those provided by ground

truth to facilitate the performance evaluation of the algorithm.

Additionally, we propose performance measures for assessing the

quality of correspondences. These measures, collectively, provide

an indication of the quality of the correspondences thus making

the registration algorithm more robust to outliers as spurious

matches are not used in computing the incremental transformation.

Keywords:

UGV, range images, registration, uncertainty, performance measures.

1. INTRODUCTION

Active range sensing has become an integral part of

any unmanned vehicle navigation system due its ability to

produce unambiguous, direct, robust, and precise images

consisting of range pixels. This is in direct contrast to passive sensing where the inference of range largely remains

computationally intensive and not robust enough for use

in natural outdoor environments. Depending on the speed

of the vehicle, operating environment, and data rate, such

range images acquired from a moving platform need to be

registered to make efficient use of information contained in

them for various navigation tasks including map-building,

localization, obstacle avoidance, and control.

Iconic methods that attempt to minimize the discrepancies between sensed data and a model of the environment

have been utilized for range registration. The attraction of

these methods lies in the fact that the matching works

directly on data points. Because the search is confined to

small perturbations of the range images, it is computationally efficient. For example, Kanade et al. [3] compared elevation maps obtained from 3D range images to determine

vehicle location. A similar iconic approach has also been

adopted by Shaffer [10] but it does not take into account

the uncertainty associated with the observation data.

We have developed a temporal iterative algorithm for

registering range images obtained from unmanned vehicles.

Formally, the process of registration is defined as follows:

Given two sets of range images (model set: M and data set:

D), find a transformation (rotation and translation) which

when applied to D minimizes a distance measure between

the two point sets. Despite the apparent simplicity of the

problem, to register range images from unmanned vehicles

traversing unstructured environments, the terrain of travel,

sensor noise and determination of accurate correspondences

make it quite challenging.

The registration algorithm is a modified variant of the

well-known Iterative Closest Point (ICP) algorithm [1]. At

each iteration, the algorithm determines the closest match

for each point and updates the estimated position based on

a least-squares metric with some modifications to increase

robustness. The modified algorithm has been shown to be

robust to outliers and false matches during the registration

of 3D range images obtained from a scanning LADAR

rangefinder on an Unmanned Ground Vehicle (UGV) and

also towards registering LADAR images from the UGV

with those from an Unmanned Aerial Vehicle (UAV) that

flies over the terrain being traversed [9]. For completeness,

the temporal iterative registration algorithm is summarized

in Section 2.

In this paper, we evaluate the performance of the registration algorithm for position estimation of UGVs operating

in unstructured environments. Field data obtained from two

trials on UGVs traversing undulating outdoor terrain is used

to quantify the performance of the algorithm in producing

continual position estimates. Using the data obtained from

the first trial, the iterative registration algorithm aids the position estimation process whenever Global Positioning System (GPS) estimates are unavailable or are below required

accuracy bounds. In the second trial, ICP is combined with

a post-correspondence Extended Kalman Filter (EKF) to

account for uncertainty present in the range images. For

both the trials, the position estimates are then compared

with those provided by ground truth to facilitate the performance evaluation of the registration algorithm. In addition,
we propose performance measures for assessing the quality

of correspondences. These measures, collectively, provide

an indication of the quality of the correspondences thus

making the registration algorithm more robust to outliers as

spurious matches are not used in computing the incremental

transformation. The registration algorithm is then combined

with proposed performance metrics and compared to the

traditional ICP algorithm in terms of accuracy and speed.

The paper is structured as below: Section 2 describes the

iterative temporal registration algorithm. Section 3 presents

experimental results when the iterative algorithm is used

for obtaining position estimates. Section 3.1 compares

registration-aided position estimates with those provided

by GPS. Section 3.2 details a map-aided registration algorithm for pose estimation. Section 4 develops performance

measures for quality assessment of correspondences within

the registration process and provides the associated results.

Section 5 provides the conclusions and outlines areas of

continuing research.

2. ITERATIVE TEMPORAL REGISTRATION ALGORITHM

The process of registration is stated formally as:

min(R,T)

X

i

||Mi − (RDi + T)||2(1)

where R is the rotation matrix, T is the translation vector

and the subscript i refers to the corresponding points of the

sets M and D.

2.1. Iterative Closest Point Algorithm

The ICP algorithm can be summarized as follows: Given

an initial motion transformation between the two point

sets, a set of correspondences are developed between data

points in one set and the next. For each point in the first

data set, find the point in the second that is closest to it

under the current transformation. It should be noted that

correspondences between the two point sets is initially

unknown and that point correspondences provided by sets

of closest points is a reasonable approximation to the true

point correspondence. From the set of correspondences, an

incremental motion can be computed facilitating further

alignment of the data points in one set to the other. This find

correspondence/compute motion process is iterated until a

predetermined threshold termination condition.

In its simplest form, the ICP algorithm can be described

by the following steps:

1. For each point in data set D, compute its closest point

in data set M. In this paper, this is accomplished via

nearest point search from the set comprising ND data

and NM model points.

2. Compute the incremental transformation (R,T) using

Singular Value Decomposition (SVD) via correspondences obtained in step 1.

3. Apply the incremental transformation from step 2. to

D.

4. If relative changes in R and T are less than a threshold,

terminate. Else go to step 1.

To deal with spurious points/false matches and to account

for occlusions and outliers, we modify and weight the leastsquares objective function in Equation (1) such that [11]:

min(R,T)

X

i

wi||Mi − (RDi + T)||2(2)

If the Euclidean distance between a point xiin one set

and its closest point yiin the other, denoted by di

4

=

d(xi, yi), is bigger than the maximum tolerable distance

threshold Dmax, then wiis set to zero in Equation (2).

This means that an xi cannot be paired with a yi since

the distance between reasonable pairs cannot be very big.

The value of Dmax is set adaptively in a robust manner by

analyzing distance statistics.

Let {xi, yi, di} be the set of original points, the set of

closest points and their distances, respectively. The mean

and standard deviation of the distances are computed as:

μ =

1

N

X

N

i=1

di; σ =

vuut

1

N

X

N

i=1

(di − μ)

2

where N is the total number of pairs.

The pseudo-code for the Adaptive Thresholding (AT) of

the distance Dmax is given below:

if μ < D

Ditnmax = μ + 3σ;

elseif μ < 3D

Ditnmax = μ + 2σ;

elseif μ < 6D

Ditnmax = μ + σ;

else Ditnmax = 2;

where itn denotes the iteration number and D is a function

of the resolution of the range data.

During implementation, D was selected based on the

following two observations:

1) If D is too small, then several iterations are required for the algorithm to converge and several good

matches will be discarded, and

2) If D is too big, then the algorithm may not converge at

all since many spurious matches will be included. The

interested reader is referred to [11] for more details on

the effect and selection of D and 2 on the convergence

of the algorithm.

At the end of this step, two corresponding point sets,

PM:{pi} and PD:{qi} are available.

The incremental transformation (rotation and translation)

of step 2. is obtained as follows:

• Calculate H=

PND

i=1(pi − pc)(qi − qc)

T

; (pc,qc) are

the centroids of the point sets (PM,PD).
• Find the Singular Value Decomposition (SVD) of H

such that H = UΩVT where U and V are unitary

matrices whose columns are the singular vectors and

Ω is a diagonal matrix containing the singular values.

• The rotation matrix relating the two point sets is given

by R = VUT.

• The translation between the two point sets is given by

T = qc − Rpc.

This process is iterated as stated in step 4. until the

mean Euclidean distance between the corresponding point

sets PM and PD is less than or equal to a predetermined

distance or until a given number of iterations is exceeded.

3. EXPERIMENTAL RESULTS

3.1. Registration-aided Position Estimation

In this section, we estimate the position of an UGV operating in an unknown outdoor environment. The registration

algorithm is used for aiding position estimation whenever

GPS errors are above a predetermined threshold1.

An Extended Kalman Filter (EKF) was used to fuse

encoder, GPS and compass observations to arrive at ground

truth position estimates. It should be noted here that the

EKF pose estimate is always superior than that provided by

GPS alone and thus has been considered as ground truth.

Consequently, a better position fix is guaranteed even when

GPS is subject to multipathing errors. The ground truth was

obtained in a similar fashion as reported in [8].

Figure 1 shows the results of the position estimation

using the registration algorithm. As mentioned earlier, registration of range images is used to aid position estimation

when GPS reported positional errors exceed a given threshold. In Figure 1(a), the registration-aided position estimates

are denoted by ‘+’ and that of the GPS by ‘◦’. The wheel

encoder estimates are also shown by ‘×’ for comparison.

The error between the GPS and the registration-aided

position estimates as compared with the ground truth are

shown in Figure 1(b). It is evident that the registration-aided

estimates are far superior than that of GPS alone.

3.2. 2D Map-aided Position Estimation

A map-aided position estimation algorithm for computing accurate pose estimates for a UGV operating in tunnellike environments is described in this section. Using ground

truth2together with the information from a range and

bearing scanning laser rangefinder, a map of the operating

domain, represented by a polyline that adequately approximates the geometry of the environment, is obtained. The

map building process relies on position estimation provided

by artificial landmarks.

1The error in the GPS positions reported were obtained as a function of

the number of satellites acquired. As an alternative, the so-called dilution

of precision measure associated with the GPS can be used for the same

purpose [2].

2The ground truth was obtained using a rotating laser scanner and

known artificial landmarks placed at surveyed locations [7].

An Iterative Closest Point-Extended Kalman Filter (ICPEKF) algorithm is used to match range images from a scanning laser rangefinder to the line segments of the polyline

map [6]. For this application, ICP alone does not provide

sufficiently reliable and accurate vehicle motion estimates.

These shortcomings are overcome by combining the ICP

with a post-correspondence EKF. Once correspondences are

established, a post-correspondence EKF, with the aid of a

non-linear observation model, provides consistent vehicle

pose estimates.

The ICP-EKF algorithm has several advantages. First,

the uncertainty associated with observations is explicitly

taken into account. Second, observations from a variety of

different sensors can be easily combined as the changes are

reflected only as additional observational states in the EKF.

Third, laser observations that do not correspond to any line

segment of the polyline map are discarded during the EKF

update stage thus making the algorithm robust to errors in

the map.

The estimated vehicle positions (solid line)3 provided by

the ICP-EKF algorithm along with the ground truth (dotted

line) is shown in Figure 2(a). The vehicle travels a distance

of 150 meters from right to left. The corresponding 2σ

confidence bounds for the absolute error in x, y and φ

are shown in Figure 2(b). It can be seen that the errors

are bounded and thus the pose estimates are consistent. It

is also clear that the estimated path is in close agreement

with the ground truth.

4. PERFORMANCE MEASURES

The correspondence determination process is the most

challenging step of the iterative algorithm. Establishing

reliable correspondences is extremely difficult as the UGV

is subjected to heavy pitching and rolling motion characteristic of travel over undulating terrain. This is further

exacerbated by the uncertainty of the location of the sensor

platform relative to the global frame of reference. In addition to these factors, noise inherently present in range

images complicates the process of determining reliable

correspondences.

One solution to overcome the above deficiencies is

to extract naturally occurring view-invariant features, for

example, corners, from range images. Such ground control

points can then be used for establishing reliable registration

with the ICP algorithm converging to the global minimum.

A hybrid approach to register aerial images obtained from

a UAV with those from the UGV was developed by augmenting the modified ICP algorithm with a feature-based

method. The feature-based hybrid approach was shown to

be effective in producing reliable registration for UGV

navigation [9].

For the map-aided position estimation scheme described

in Section 3.2, the ICP-EKF algorithm failed to produce

3As the estimates and the their corresponding ground truth are very

close, extra effort is required on the part of the reader to distinguish

between the two.
−0.4 −0.2 0 0.2 0.4 0.6 0.8 1 1.2

−18

−16

−14

−12

−10

−8

−6

−4

−2

0

Position Estimates

X [m]

Y [m]

(a)

0 10 20 30 40 50 60 70 80 90 100

−0.5

0

0.5

1

1.5

2

Position Errors

X [m]

0 10 20 30 40 50 60 70 80 90 100

−2

−1

0

1

2

3

4

5

Y [m]

(b)

Fig. 1. Registration-aided position estimation. The aided estimates are shown by ‘+’ and that of GPS by ‘◦’. The wheel encoder estimates shown by

‘×’ are included for comparison. In (b), position errors as compared to the ground truth is depicted (GPS estimate is shown in dashed-dotted line).

unambiguous correspondences with the map whenever variations in data sets were not unique. To enable ICP to produce accurate correspondences, a strategy to augment the

ICP-EKF algorithm with artificial/natural landmarks was

devised to provide external aiding. To facilitate the selection

of landmarks, an entropy-based metric was developed to

enable the evaluation of information contained in a potential

landmark. A curvature scale space algorithm was developed

to extract natural landmarks from laser rangefinder scans

[5]. The proposed landmark augmentation methodology has

been verified for the localization of a Load-Haul-Dump

truck and resulted in the ICP-EKF algorithm producing

reliable and consistent estimates [6].

We propose the following measures towards performance

evaluation of the registration algorithm for position estimation.

4.1. ICP Estimate and Dead-reckoning Prediction Measure

The ICP itself can be used to compute the estimates of

the pose of the UGV. This can be compared with dead-
40 50 60 70 80 90 100 110 120 130 140

−30

−20

−10

0

10

20

30

40

50

 Estimated Vehicle Path

X [m]

Y [m]

ICP−EKF 

Gnd. Tth.

(a)

30 40 50 60 70 80 90 100 110 120

−2

−1

0

1

2

2σ bounds for x, y and Φ

σ

x [m]

30 40 50 60 70 80 90 100 110 120

−2

−1

0

1

2

σ

y [m]

30 40 50 60 70 80 90 100 110 120

−0.4

−0.2

0

0.2

0.4

time [sec]

σ

Φ [rad]

(b)

Fig. 2. 2D Map-aided Position Estimation. ICP-EKF estimated position

the trial vehicle (solid line) and the ground truth (dotted line) are shown in

(a). The 2σ confidence bounds are computed using the covariance estimate

for the error in x, y and φ compared to the actual error computed with

the ground truth estimates as depicted in (b).

reckoning estimates each time before the correspondences

are computed. More specifically, the prediction covariance

(from dead-reckoning) can be utilized as a check on the ICP

estimates, since if the associated state covariances become

large, this is an indication of the state estimation filter

divergence as a result of the poor ICP estimates.

The largest Eigen value of the predicted state covariance

matrix (that is a measure of the total positional uncertainty)

can be used as a measure to check the quality of the ICP

estimates.

Also the determinant of the predicted state covariance

matrix can be used as a measure since it represents total

predicted uncertainty and this can be observed to see if the

ICP produces reliable and non-divergent estimates (since

once the ICP estimates start behaving erratically, this is

reflected by similar behavior in the correspondences).

4.2. Mean Squared Error Measure

To indicate if the correspondences make sense the following measure is proposed:

Pmse =

1

n

Xn

i=1

[d (pi, `i)]2

where pi and `i are the i

th of n range data points and

d (pi, `i) is the distance from the p

th

i

point to the `

th

i

point.

Global minimum of the function will occur at the true pose

of the vehicle.

At the true pose, all or at least the majority of the range

data points will be close to their corresponding points, thus

yielding a very low value for the correct solution. The

problem with this measure is that it is difficult to decide if

the pose is true in the presence of outliers and occlusions.

4.3. Classification Factor

Similar to [4], we define well defined data points as those

points that lie within some distance threshold from their

corresponding points:

Pcf =

1

n

Xn

i=1

μ

1 −

d

m

dm + cm

¶

where d = d(pi, `i), c = neighborhood size, m = sigmoid

steepness4. At true pose, global maximum should approach

close to unity and will be less in the neighborhood of well

defined data points. Note that Pcf values can fall only

between [0,1].

Indirectly this measure indicates the future-goodness of

the pose estimate if a certain threshold is exceeded. The

problem with this measure could be that it is not as

sensitive as Pmse since it applies only for a certain local

neighborhood. Thus Pmse can be used as a comparative

performance measure whereas Pcf for pass/fail decisions

for the correspondences before they are passed on for

computing the incremental transformation.

4.4. Comparative Performance Measure

It is the ratio defined by

Pcpm =

Pcf

2

Pmse

The peak of this measure should occur at the true pose.

In other words, this measure serves as a nonlinear scaling

factor applied to the inverse of the measure, Pmse.

4A sigmoid function is given by f(a) = 1

1+e−ga where g denotes

gain.
4.5. Results and Discussion

In this section, we use 3D LADAR data obtained during

field trials to illustrate the utility of the proposed metrics

in assessing the quality of correspondences. The LADAR

was mounted on a UGV traversing rugged terrain on a

pan/tilt platform to increase its narrow 20◦ field of view.

The range of the tilt motion is ±30◦resulting in an effective

field of view of about 90◦and providing a range image

of 32 lines × 180 pixels where each data point contains

the distance to a target in the operating environment. The

angular resolution of this LADAR is 0.658◦ × 0.5

◦

in the

horizontal and vertical directions, respectively.

We illustrate the combined utility of adaptive thresholding and the Pmse measure by using it to register 3D range

images. We then compare the registration results with direct

ICP (i.e., without AT and Pmse). For the comparison, the

same termination threshold condition is employed for both

the algorithms.

Figures 3 and 4 summarize the comparative results.

Figures 3(a) and (b) show the registered LADAR images

via the direct and combined ICP algorithms, respectively.

The combined ICP needed 39 iterations whereas the direct

ICP took 82 iterations. The mean distances before and after

registration were 0.19 m and 0.07 m for the two algorithms,

respectively. Figures 4(a) and (b) show the closest point

distance before and after registration. It is thus evident

that the combined ICP algorithm is vastly superior than

the direct ICP algorithm both in terms of accuracy and

speed. Even though the Pmse metric is sensitive to outliers,

we contend that the adaptive thresholding methodology in

combination with the mean-squared error metric provides

an acceptable means in inferring the validity of the position

estimate.

5. CONCLUSIONS AND FURTHER WORK

The evaluation of performance of an iterative registration

algorithm for position estimation of UGVs operating in

unstructured environments was the main theme of this

paper. The modified ICP algorithm was used to aid the

position estimation process and the resulting estimates were

compared with ground truth to facilitate the performance

evaluation for two sets of field data. Field data obtained

from trials on UGVs traversing undulating outdoor terrain

was used to quantify the performance of the algorithm in

producing continual position estimates.

In the first set of experimental results, registration-aided

position estimates were generated whenever GPS estimates

were unavailable or unreliable. For the second set of trials,

the ICP-EKF algorithm was used for map-aided position

estimation. In both cases, the presented results demonstrated the efficacy of the registration algorithm for position

estimation.

The second part of the paper developed performance

measures towards assessing the quality of correspondences

required for accurate and efficient registration. The modified algorithm was combined with the mean-squared error

metric to register 3D LADAR range images. The combined

algorithm was then evaluated against the direct ICP algorithm. The accompanying results showed the superiority

of the combined algorithm both in terms of speed and

accuracy.

Future work includes combining the measures to achieve

efficient 3D registration for mapping and position estimation tasks, both in indoor and outdoor environments.

Currently, we are in the process of obtaining LADAR data

in areas where GPS accuracy degrades and then approaches

its best estimate. Such data sets would be of immense value

in evaluating the utility of the registration algorithm and the

proposed performance measures.

6. REFERENCES

[1] P. Besl and N. McKay. A Method for Registration of 3-D Shapes.

IEEE Transactions on Pattern Analysis and Machine Intelligence,

14(2):239–256, 1992.

[2] M.S. Grewal, L.R. Weill, and A.P. Andrews. Global Positioning

Systems, Inertial Navigation and Integration. Wiley, 2001.

[3] I. Kweon and T. Kanade. High Resolution Terrain Map from

Multiple Sensor Data. In Proceedings of the IEEE International

Workshop on Intelligent Robots and Systems, volume 1, pages 127–

134, 1990.

[4] P. MacKenzie and G. Dudek. Precise Positioning using Model-based

Maps. In Proceedings of the IEEE International Conference on

Robotics and Automation, pages 1615–1621, 1994.

[5] R. Madhavan and H. Durrant-Whyte. Natural Landmark-based

Autonomous Navigation using Curvature Scale Space. Robotics and

Autonomous Systems, 46(2):79–95, February 2004.

[6] R. Madhavan and H. Durrant-Whyte. Terrain Aided Localization

of Autonomous Ground Vehicles. Special Issue of the Journal of

Automation in Construction (Invited), 13(1):69–86, January 2004.

[7] R. Madhavan et al. Evaluation of Internal Navigation Sensor Suites

for Underground Mining Vehicle Navigation. In Proceedings of the

IEEE International Conference on Robotics and Automation, pages

999–1004, May 1999.

[8] R. Madhavan, K. Fregene, and L.E. Parker. Distributed Cooperative Outdoor Multi-robot Localization and Mapping. Autonomous

Robots: Special Issue on Analysis and Experiments in Distributed

Multi-Robot Systems, 17(1):23–39, July 2004.

[9] R. Madhavan, T. Hong, and E. Messina. Temporal Range Registration for Unmanned Ground and Aerial Vehicles. In Proceedings

of the IEEE International Conference on Robotics and Automation,

pages 3180–3187, April 2004.

[10] G. Shaffer. Two-Dimensional Mapping of Expansive Unknown

Areas. PhD thesis, Carnegie Mellon University, 1992.

[11] Z. Zhang. Iterative Point Matching for Registration of Free-Form

Curves and Surfaces. International Journal of Computer Vision,

13(2):119–152, 1994.
(a) Direct ICP

(b) Modified ICP with AT and Pmse

Fig. 3. Illustration of 3D LADAR registration via the direct (w/o AT and Pmse) and combined ICP algorithms. The model (‘◦’) and data (‘+’) points

after registration are shown.

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

0

0.5

1

1.5

2

2.5

Data Points

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Closest Point Distance Before and After Registration

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registered

(a)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

0

0.5

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Closest Point Distance Before and After Registration

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Fig. 4. The registered (shown in dashed-dotted line) and unregistered closest point distances are shown corresponding to the registration of range

images depicted in Figures 3(a) and 3(b), respectively.
Evaluating System Capabilities and User Performance in the Battlefield

Augmented Reality System 

Mark A. Livingston†J. Edward Swan II† Simon J. Julier‡ Yohan Baillot‡

Dennis Brown† Lawrence J. Rosenblum†Joseph L. Gabbard§ Tobias H. Hollerer  ̈

¶

Deborah Hix§

Naval Research Laboratory

Washington D.C.

Abstract

We describe a first experiment in evaluating the system

capabilities of the Battlefield Augmented Reality System, an

interactive system designed to present military information

to dismounted warfighters. We describe not just the current

experiment, but a methodology of both system evaluation

and user performance measurement in the system, and show

how both types of tests will be useful in system development.

We summarize results in a perceptual experiment being used

to inform system design, and discuss ongoing and future

experiments to which the work described herein leads.

1 Introduction

One of the most challenging aspects of the design of

intelligent systems is the user interface – how the user

will perceive and understand the system. Our application

presents military information to a dismounted warfighter.

In order to both refine the system’s capabilities and improve the warfighter’s performance of tasks while using the

system, we measure human performance using our system,

even while early in the design phase of the user interface.

This paper describes an early experiment in the context of

system evaluation and describes implications for both system and human performance metrics as they apply to such

systems.

1.1 Application context

Military operations in urban terrain (MOUT) present

many unique and challenging conditions for the warfighter. 

Portions of this paper were originally published in [10] and [11].

†Virtual Reality Laboratory, Naval Research Laboratory. Corresponding email: livingston@ait.nrl.navy.mil

‡

ITT Advanced Engineering and Sciences

§Systems Research Center, Virginia Polytechnic Inst. and State Univ.

¶Dept. of Computer Science, University of California, Santa Barbara

The environment is extremely complex and inherently

three-dimensional. Above street level, buildings serve varying purposes (such as hospitals or communication stations).

They can harbor many risks, such as snipers or mines,

which can be located on different floors. Below street level,

there can be an elaborate network of sewers and tunnels.

The environment can be cluttered and dynamic. Narrow

streets restrict line of sight and make it difficult to plan and

coordinate group activities. Threats, such as snipers, can

continuously move and the structure of the environment itself can change. For example, a damaged building can fill

a street with rubble, making a once-safe route impassable.

Such difficulties are compounded by the need to minimize

the number of civilian casualties and the amount of damage

to civilian targets.

In principle, many of these difficulties can be overcome

through better situation awareness. The Concepts Division

of the Marine Corps Combat Development Command (MCCDC) concludes [2]:

Units moving in or between zones must be able

to navigate effectively, and to coordinate their activities with units in other zones, as well as with

units moving outside the city. This navigation

and coordination capability must be resident at

the very-small-unit level, perhaps even with the

individual Marine.

A number of research programs have explored the means

by which navigation and coordinated information can be delivered to the dismounted warfighters. We believe a mobile

augmented reality system best meets the needs of the dismounted warfighter.

1.2 Mobile Augmented Reality

Augmented reality (AR) refers to the mixing of virtual

cues from the real three-dimensional environment into the

user’s perception. In this work, AR denotes the 3D merging
Figure 1. A sample view of our system, showing

one physically visible building with representations of three buildings which it occludes.

of synthetic imagery into the user’s natural view of the surrounding world, using an optical, see-through, head-worn

display.

A mobile augmented reality system consists of a computer, a tracking system, and a see-through HMD. The system tracks the position and orientation of the user’s head

and superimposes graphics and annotations that are aligned

with real objects in the user’s field of view. With this

approach, complicated spatial information can be directly

aligned with the environment. This contrasts with the use of

hand-held displays and other electronic 2D maps. With AR,

for example, the name of a building could appear as a ”virtual sign post” attached directly to the side of the building.

To explore the feasibility of such a system, we are developing the Battlefield Augmented Reality System (BARS). Figure 1 is an example from BARS. This system will network

multiple dismounted warfighters together with a command

center.

Through the ability to present direct information overlays, integrated into the user’s environment, AR has the potential to provide significant benefits in many application

areas. Many of these benefits arise from the fact that the virtual cues presented by an AR system can go beyond what

is physically visible. Visuals include textual annotations,

directions, instructions, or “X-ray vision,” which shows objects that are physically present, but occluded from view.

Potential application domains include manufacturing [1],

architecture [20], mechanical design and repair [7], medical

applications [4, 17], military applications [11], tourism [6],

and interactive entertainment [19].

1.3 Performance Measurement in BARS

BARS supports information gathering and human navigation for situation awareness in an urban setting [11]. A

critical aspect of our research methodology is that it equally

addresses both technical and human factors issues in fielding mobile AR. AR system designers have long recognized

the need for standards for the performance of AR technology. As the technology beginsto mature, we and some other

research groups are also considering how to test user cognition when aided by AR systems.

We determined the task in which to measure performance first through consultation with domain experts [9].

They identified a strong need to visualize the spatial locations of personnel, structures, and vehicles occluded by

buildings and other urban structures during military operations in urban terrain. While we can provide an overhead map view to view these relationships, using the map

requires a context switch. We are designing visualization

methods that enable the user to understand these relationships when directly viewing, in a heads-up manner, the augmented world in front of them.

The perceptual community has studied depth and layout perception for many years. Cutting [3] divides the visual field into three areas based on distance from the observer: near-field (within arms reach), medium-field (within

approximately 30 meters), and far-field (beyond 30 meters).

He then points out which depth cues are more or less effective in each field. Occlusion is the primary cue in all

three spaces, but with the AR metaphor and the optical seethrough, this cue is diminished. Perspective cues are also

important for far-field objects, but this assumes that they

are physically visible. The question for an AR system is

which cues work when the user is being shown virtual representations of objects integrated into a real scene.

Our immediate goal is thus to determine methods that

are appropriate for conveying depth relationships to BARS

users. This requires measurement of the system’s performance in presenting information that feed the users’ perceptions of the surrounding environment. Then, we need to

establish a standard for warfighter performance in the task

of locating military personnel and equipment during an operation in urban terrain. For example, one goal of our work

is to determine how many depth layers a user can understand.

2 Related Work

2.1 Perceptual Measures in AR Systems

A number of representations have been used to convey

depth relationships between real and virtual objects. Partial

transparency, dashed lines, overlays, and virtual cut-away

views all give the user the impression of a difference in the

depth [7, 16, 20, 12].
Furmanski et al. [8] utilized a similar approach in their

pilot experiment. Using video AR, they showed users a

stimulus which was either behind or at the same distance

as an obstructing surface. They then asked users to identify

whether the stimulus was behind, at the same distance as,

or closer than the obstruction. The performance metric here

is thus an ordinal depth measure. Only a single occluded

object was present in the test. The parameters in the pilot

test were the presence of a cutaway in the obstruction and

motion parallax. The presence of the cutaway significantly

improved users’ perceptions of the correct location when

the stimulus was behind the obstruction. The authors offered three possible locations to the users, even though only

two locations were used. Users consistently believed that

the stimulus was in front of the obstruction, despite the fact

that it was never there.

Ellis and Menges [5] found that the presence of a visible

(real) surface near a virtual object significantly influences

the user’s perception of the depth of the virtual object. For

most users, the virtual object appeared to be nearer than it

really was. This varied widely with the user’s age and ability to use accommodation, even to the point of some users

being influenced to think that the virtual object was further away than it really was. Adding virtual backgrounds

with texture reduced the errors, as did the introduction of

virtual holes, similar to those described above. Rolland et

al. [13] found that occlusion of the real object by the virtual object gave the incorrect impression that the virtual object was in front, despite the object being located behind

the real object and other perceptual cues denoting this relationship. Further studies showed that users performed better when allowed to adjust the depth of virtual objects than

when making forced-choice decisions about the objects’ locations [14].

2.2 Cognitive Measures in AR Systems

There have been few user studies conducted with AR

systems; most such studies (including ours) have been at

the perceptual level, such as those described above. The

recent emergence of hardware capable of delivering sufficient performance to achieve stable presentation of graphics does enable such studies, however. One example of a

cognitive-level study is the application of AR to medical

interventions with ultrasound guidance [15]. In this trial,

a doctor performed ultrasound-guided needle biopsies with

and without the assistance of an AR system that had been

designed for the task. A second physician evaluated the needle placement of the first. The analysis showed that needle

localization was improved when using the AR system. The

performancemetricsin thistrial were the standard for evaluating doctors’ performance used by medical schools: needle

placement at various locations within the target lesion. The

physician uses the ultrasound to determine the ideal and actual needle locations. Thus the measure is tightly connected

to the task, and in fact exists prior to the development of the

AR system.

3 Experiment

As noted above, we have begun our performance measurements with the subsystem that depicts occluded surfaces. The first test we performed was a perceptual experiment to determine whether the system provides sufficient

information for the user to understand three layers of depth

among large objects that are occluded from view.

3.1 Design Methodology

From our initial design work and review by colleagues,

we selected three graphical parameters to vary in our representations: drawing style, opacity, and intensity. These

comprised a critical yet tenable set of parameters for our

study. We used an urban environment that fit our laboratory

facilities. By sitting in the atrium of our building, a user

could wear an indoor-based version of our system (which

is more powerful than the current mobile prototypes). The

environment included one physically visible building and

two occluded buildings. Among the two occluded buildings we placed one target to locate in one of three different

positions: closer than the two occluded buildings, between

the two, or behind both. This introduced the question of

whether the ground plane (i.e. perspective) would provide

the only cue that users would actually use. Because our application may require users to visualize objects that are not

on the ground or are at a great distance across hilly terrain,

we added the use of a consistent, flat ground plane for all

objects as a parameter.

3.2 Hardware

The hardware for our AR platform consisted of three

components. For the image generator, we used a Pentium IV 1.7 GHz computer with an ATI FireGL2 graphics

card (outputting frame-sequential stereo). For the display

device, we used a Sony Glasstron LDI–100B stereo optical see-through display (SVGA resolution, 20

horizontal

field of view in each eye). The user was seated indoors

for the experiment and was allowed to move and turn the

head and upper body freely while viewing the scene, which

was visible through an open doorway to the outdoors. We

used an InterSense IS-900 6-DOF ultrasonic/inertial hybrid

tracking system to track the user’s head motion to provide a

consistent 3D location for the objects as the user viewed the

world. The IS-900 provides position accuracy to 3.0 mm

and orientation accuracy to 1  0

.

The user entered a choice for each trial on a standard

extended keyboard, which was placed on a stand in front

of the seat at a comfortable distance. The display device,

whose transparency can be adjusted in hardware, was set
for maximum opacity of the LCD, to counteract the bright

sunlight that was present for most trials. Some trials did

experience a mix ofsunshine and cloudiness, but the opacity

setting was not altered. The display brightness was set to the

maximum.

The display unfortunately does not permit adjustment of

the inter-pupillary distance (IPD) for each user. If IPD is

too small, then the user will be seeing slightly cross-eyed

and tend to believe objects are closer than they are. The display also does not permit adjusting the focal distance of the

graphics. The focal distance of the virtual objects is therefore closer than the real object that we used as the closest

obstruction. This would tend to lead users to believe the

virtual objects were closer than they really were.

Stereo is considered a powerful depth cue at near-field

distances (approximately 1.0 meters, or about at arm’s

length). At far-field distances, such as the task we gave

our users, stereo is not considered to be a strong depth cue;

however, we wanted to be able to provide some statistical

evidence for this claim. Many practitioners of AR systems

have noted that improper settings of parameters related to

stereo imagery (such as IPD and vergence) can lead to user

discomfort in the form of headaches or dizziness. None of

users reported any such problems; they wore the device for

an average of 30 minutes. These issues will need to be addressed in future versions of the hardware for AR systems,

but are beyond the scope of our work.

3.3 Experimental Design

3.3.1 Independent Variables

From our heuristic evaluation and from previous work, we

identified the following independent variablesfor our experiment. These were all within-subject variables; every user

saw every level of each variable.

Drawing Style (“wire”, “fill”, “wire+fill”): Although the

same geometry was visible in each stimulus (except for

which target was shown), the representation of that geometry was changed to determine what effect it had on depth

perception. We used three drawing styles (Figure 2). In

the first, all objects are drawn as wireframe outlines. In

the second, the first (physically visible) object is drawn as a

wireframe outline, and all other objects are drawn with solid

fill (with no wireframe outline). In the third style, the first

object is in wireframe, and all other layers are drawn with

solid fill with a white wireframe outline. Backface culling

was on for all drawing styles, so that the user saw only two

faces of any occluded building.

Opacity (constant, decreasing): We designed two sets of

values for the α channel based on the number of occluding

objects. In the “constant” style, the first layer (visible with

registered wireframe outline) is completely opaque, and all

other layers have the same opacity (α  0  5). In the “decreasing” style, opacity changes for each layer. The first

Figure 3. The experimental design (not to scale)

shows the user position at the left. Obstruction 1

denotes the visible surfaces of the physically visible building. The distance from the user to obstruction 1 is approximately 60 meters. The distance from the user to target location 3 is approximately 500 meters, with the obstructions and target locations roughly equally spaced.

(physically visible, wireframe) layer is completely opaque.

The successive layers are not opaque; the α values were 0  6,

0  5, and 0  4 for the successively more distant layers.

Intensity (constant, decreasing): We used two sets of intensity modulation values. The modulation value was applied to the object color (in each color channel, but not in the

opacity or α channel) for the object in the layer for which it

was specified. In the “constant” style, the first layer (visible

with registered wireframe outline) has full intensity (modulator=1.0) and all other layers have intensity modulator=0.5.

In the “decreasing” style, the first layer has its full native intensity, but successive layers are modulated as a function of

occluding layers: 0.75 for the first, 0.50 for the second, and

0.25 for the third (final) layer.

Target Position (close, middle, far): As shown in the

overhead map view (Figure 3), there were three possible

locations for the target.

Ground Plane (on, off): From the literature and everyday experience, we know that the perspective effects of the

ground plane rising to meet the horizon and apparent object

size are a strong depth cues. In order to test the representations as an aide to depth ordering, we removed the ground

plane constraint in half of the trials. The building sizes were

chosen to have the same apparent size from the users’ location for all trials. When the ground plane constraint was

not present in the stimulus, the silhouette of each target was

fixed for a given pose of the user. In other words, targets

two and three were not only scaled (to yield the same apparent size) but also positioned vertically such that all three

targets would occupy the same pixels on the 2D screen for

the same viewing position and orientation. No variation in

position with respect to the two horizontal dimensions was

necessary when changing from using the ground plane to

not using it. The obstructions were always presented with

the same ground plane. We informed the users for which
Figure 2. User’s view of the stimuli. Left: “wire” drawing style. Center: “fill” drawing style. Right: “wire+fill”

drawing style. The target (smallest, most central box) is between (position “middle”) obstructions 2 and 3 in all

three pictures. These pictures were acquired by placing a camera to the eyepiece of the HMD, which accounts

for the poor image quality. The vignetting and distortion are due to the camera lens and the fact that it does not

quite fit in the exit pupil of the HMD’s optics.

half of the session the ground plane would be consistent between targets and obstructions.

We did this because we wanted to remove the effects of

perspective from the study. Our application requires that we

be able to visualize objects that may not be on the ground,

may be at a distance and size that realistic apparent size

would be too small to discern, and may be viewed over hilly

terrain. Since our users may not be able to rely on these

effects, we attempted to remove them from the study.

Stereo (on, off): The Sony Glasstron display receives as

input left- and right-eye images. The IPD and vergence angle are not adjustable, so we can not provide a true stereo

image for all users. However, we can present images with

disparity (which we call “stereo” for the experiment) or

present two identical images (“biocular”).

Repetition (1, 2, 3): Each user saw three repetitions of

each combination of the other independent variables. It

is well-known that users will often improve their performance with repetition of the same stimulus within an experiment. By repeating the stimuli, we can gain some insight into whether the user needs to learn how the system

presents cues or whether the system presents intuitive cues.

If there is no learning effect with repetition of stimuli, then

we can infer that the users had whatever collective performance they achieved intuitively.

3.3.2 Dependent Variables

For each trial, we recorded the user’s (three-alternative

forced) choice for the target location and the time the user

took to enter the response after the software presented the

stimulus. We opted to ask the user only to identify the ordinal depth, not an absolute distance between the graphical

layers. This implied the forced-choice design.

All combinations of these parameters were encountered

by each user; however, the order in which these were presented was also randomly permuted. Thus each user viewed

432 trials. The users ranged in time from twenty to forty

minutes for the complete set of trials. The users were told

Figure 4. Experimental design and counterbalancing for one user. Systematically varied parameters

were counterbalanced between subjects.

to make their best guess upon viewing the trial and not to

linger; however, no time limit per trial was enforced. The

users were instructed to aim for a balance of accuracy and

speed, rather than favoring one over the other.

3.3.3 Counterbalancing

In order to reduce time-based confounding factors, we

counterbalanced the stimuli. This helps control learning and

fatigue effects within each user’s trials and factors such as

the amount of sunshine that change between subjects beyond our control. Figure 4 describes how we counterbalanced the stimuli. We observed (in conjunction with many

previous authors) that the most noticeable variable was the

presence of the ground plane [3, 18]. In order to minimize

potentially confusing large-scale visual changes, we gave

ground plane and stereo the slowest variation. Following

this logic, we next varied the parameters which controlled

the scene’s visual appearance (drawing style, alpha, and in-
tensity), and within the resulting blocks, we created nine

trials by varying target position and repetition.

3.4 Experimental Task

We designed a small virtual world that consisted of four

buildings (Figure 3), with three potential target locations.

The first building was an obstruction that corresponded (to

the limit of our modeling accuracy) to a building that was

physically visible during the experiment. The obstructions

were always drawn in blue; the target always appeared in

red. The target was scaled such that its apparent 2D size

was equal, regardless of its location. Obstructions 2 and 3

roughly corresponded to real buildings. The three possible

target locations did not correspond to real buildings.

The task for each trial was to determine the location of

the target that was drawn. The user was shown the overhead

view before beginning the experiment. This helped them

visualize their choices and would be an aide available in a

working application of our system. The experimenter explained that only one target would appear at a time. Thus in

all of the stimulus pictures, four objects were visible: three

obstructions and the target. For the trials, users were instructed to use the number pad of a standard extended keyboard and press a key in the bottom row of numbers (1–3)

if the target were closer than obstructions 2 and 3, a key

in the middle row (4–6) if the target were between obstructions 2 and 3, or a key in the top row (7–9) if the target were

further than obstructions 2 and 3. A one-second delay was

introduced between trials within sets, and a rest period was

allowed between sets for as long as the user wished. We

showed the user 48 sets of nine trials each. The users reported no difficulties with the primitive interface after their

respective practice sessions. The users did not try to use

head motion to provide parallax, which is not surprising for

a far-field visualization task.

3.5 Subjects

Eight users completed the experiment (432 trials each).

All subjects were male and ranged in age from 20 to 48. All

volunteered and received no compensation. Our subjects reported being heavy computer users. Two were familiar with

computer graphics, but none had seen our representations.

Subjects did not have difficulty learning or completing the

experiment.

Before the experiment, we asked users to complete a

stereo acuity test, in case stereo had produced an effect. The

test pattern consisted of nine shapes containing four circles

each. For each set of four circles, the user was asked to

identify which circle was closer than the other three. Seven

users answered all nine test questions correctly, while the

other user answered eight correctly.

4 Hypotheses

We made the following hypotheses about our independent variables.

1. The ground plane would have a strong positive effect

on the user’s perception of the relative depth.

2. The wireframe representation (our system’s only option before this study) would have a strong negative

effect on the user’s perception.

3. Stereo imagery would not yield different results than

biocular imagery, since all objects are in the farfield [3].

4. Decreasing intensity would have a strong positive effect on the user’s perception for all representations.

5. Decreasing opacity would have a strong positive effect

on the user’s perception of the “fill” and “wire+fill”

representations. In the case of wireframe representation the effect would be similar to decreasing intensity. Apart from the few pixels where lines actually

cross, decreasing opacity would let more and more of

the background scene shine through, thereby indirectly

leading to decreased intensity.

5 Results

There are a number of error metrics we apply to the experimental data. Figure 5 categorizes the user responses.

Subjects made 79% correct choices and 21% erroneous

choices. We found that subjects favored the far position,

choosing it 39% of the time, followed by the middle position (34%), and then by the close position (27%). We also

found that subjects were the most accurate in the far position: 89% of their choices were correct when the target was

in the far position, as compared to 76% correct in the close

position, and 72% correct in the middle position.

As discussed above, we measured two dependent variables: user response time, and user error. For user response time, the system measured the time in milliseconds

(ms) between when it drew the scene and when the user responded. Response time is an interesting metric because it

indicates how intuitive the representations are to the user.

We want the system to convey information as naturally as

the user’s vision does in analogous real-world situations.

For user error, we calculated the metric e 



a  u



, were

a is the actual target position (between 1 and 3), and u is the

target position chosen by the user (also between 1 and 3).

Thus, if e  0 the user has chosen the correct target; if e  1

the user is off by one position, and if e  2 the user is off by

two positions.

We conducted significance testing for both response

time and user error with a standard analysis of variance
F


M


C


Target Position


Number of Responses


875


44


224


835


119


53


273


1028


5


Figure 5. User responses by target position. For

each target position, the bars show the number

of times subjects chose the (C)lose, (M)iddle, and

(F)ar positions. Subjects were either correct when

their choice matched the target position (white), off

by one position (light gray), or off by two positions

(dark gray).

(ANOVA) procedure. In the summary below, we report user

errors in positions (pos).

We briefly discuss the factors that affected user performance. As we expected, subjects were more accurate when

a ground plane was present (  1435 pos) then when it was

absent (  3056 pos). Interestingly, there was no effect of

ground plane on response time  F  1	 . This indicates that

subjects did not learn to just look at the ground plane and

immediately respond from that cue alone, but were in fact

also attending to the graphics.

Figure 6 shows that subjects were slower using the

“wire” style than the “fill” and “wire+fill” styles. Subjects

had the fewest errors with the “wire+fill” style. These results verified our hypotheses that the “wire” style would

not be very effective, and the “wire+fill” style would be the

most effective, since it combines the occlusion properties

of the “fill” style with the wireframe outlines, which help

convey the targets’ shapes.

Subjects were more accurate with decreasing opacity

(  1962 pos) than with constant opacity (  2529 pos). This

makes sense because the decreasing opacity setting made

the difference between the layers more salient. Subjects

were both faster (2340 versus 2592 ms) and more accurate

(  1811 versus  2679 pos) with decreasing intensity. This result was expected, as decreasing intensity did a better job

of differentiating the different layers. However, Figure 7

shows that the effect on response time is due to the difference between constant and decreasing intensity when the

target is drawn in the “wire” style.

As expected from training effects, subjects became faster

with repetition. However, repetition had no effect on absolute error  F  1	 , so although subjects became faster, they

0


500


1000


1500


2000


2500


3000


3500


wire
 fill
 wire+fill


Drawing Style


Response Time


(Milliseconds)


0.1


0.15


0.2


0.25


0.3


0.35


0.4


0.45


0.5


Error (Positions)


Mean Response Time


Mean Error


±1 std error


Figure 6. Main effect of drawing style on response

time (
) and error ().

2000


2200


2400


2600


2800


3000


3200


3400


3600


wire
 fill
 wire+fill


Drawing Style


Response Time (Milliseconds)


const


decr


Intensity
 ±1 std error


Figure 7. Drawing style by intensity (constant (
),

decreasing ()) interaction on response time.

did not become more accurate. This can be taken as a sign

that the presented visuals were understandable for the subjects right from the outset. No learning effect took place

regarding accuracy. Subjects became faster, though, which

is a sign that their level of confidence increased.

6 Discussion

In a broad context, we believe that our methodology will

enable us to evaluate both system capabilities and user performance with the system. Human perception is an innate

ability, and variations in performance will reflect the system’s appropriateness for use by dismounted warfighters.

Thus, we are really evaluating the system’s performance by

measuring the user’s performance on perceptual-level tasks.

The evaluation of cognitive-level tasks will enable us to determine how users are performing. Such high-level metrics

can only be measured after the results of the perceptual-
0.05


0.1


0.15


0.2


0.25


0.3


0.35


0.4


0.45


0.5


wire
 fill
 wire+fill


Drawing Style


Error (Positions)


const


decr


Intensity
 ±1 std error


Figure 8. Drawing style by intensity (constant (
),

decreasing ()) interaction on absolute error.

level tests inform the system design.

Our first experiment has given insight into how users perceive data presented in the system. The application of our

results to human perception and thus our system design are

straightforward. It is well-known that a consistent ground

plane (a perspective constraint) is a powerful depth cue.

However, we can now provide statistical backing for our

fundamental hypothesis that graphical parameters can provide strong depth cues, albeit not physically realistic cues.

We found that with the ground plane on the average error

was  144 pos, whereas the with the ground plane off and the

following settings: 

drawing style: “wire+fill” 

opacity: decreasing 

intensity: decreasing

the average error was  111 pos. The data thus suggest that

we did find a set of graphical parameters as powerful as the

presence of the ground plane constraint. This would indeed

be a powerful statement, but requires further testing before

we can say for sure whether this is our finding. As a secondary result, the fact that there was a main effect of repetition on response time but not on accuracy indicates that

the subjects could quickly understand the semantic meaning

of the encodings. This validates that BARS is performing

at a level that is sufficient for users to consistently (but not

always) identify the ordinal depth among three occluded objects.

There are several next steps available to us. Further

perceptual-level testing will demonstrate whether these results extend to more complex scenes (with more layers of

depth). We are currently designing a follow-up study that

will use not just an ordinal depth metric, but an absolute

distance metric. This study will task the user to move a virtual object into depth alignment with real objects. We are

developing metrics to apply to the user’s control of the object, such as the number of oscillations they use to place the

object into position, that will give us insight into their confidence in the depth estimates they perceive through BARS.

We are also considering ways in which to measure the user’s

subjective reaction to the system, as this is also an important

aspect of the system’s capabilities.

Once these results inform our future system design, we

will move up to cognitive-level testing, in which we hope

to have multiple users wear prototype systems in an urban

environment. We can have users identify locations of objects relative to maps or to each other. We could have users

retrieve objects from the environment. The metrics we plan

to use will reflect the cognition required. Distance and response time will remain interesting measures, but now the

absolute distance will become more important. We will be

able to add directional measures as well, concomitant with

the increased complexity of the task for a mobile user. Since

our application is designed for a military context, we intend to design our cognitive-level tests in conjunction with

military domain experts and have at least some of the subjects in our studies be active members of the military. This

introduces the opportunity to measure system performance

by comparing against current performance of dismounted

warfighters in these tasks. This combined design and evaluation methodology will enable us to evaluate the Battlefield

Augmented Reality System and its users.

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1996.
Measuring Cooperative Robotic Systems Using Simulation-Based Virtual 

Environment 

Xiaolin Hu 

Computer Science Department 

Georgia State University, Atlanta GA, USA 30303 

Bernard P. Zeigler 

Arizona Center for Integrative Modeling and Simulation 

University of Arizona, Tucson AZ, USA 85721 

ABSTRACT 

Simulation-based study plays an important role in experimenting, 

understanding, and evaluating intelligent robotic systems. While 

robot models can be created and studied in a simulated environment, 

replacing some of the robot models with their real robot counterparts 

brings simulation-based study one step closer to the reality. It also 

provides the flexibility to allow real robots to be experimented 

within a virtual environment. This capability of robot-in-the-loop 

simulation is especially useful for large-scale cooperative robotic 

systems whose complexity and scalability severely limit the 

possibility for study and evaluation in a physical environment with 

real robots. This paper presents a simulation-based approach that 

allows a cooperative robotic system to be effectively evaluated in a 

virtual environment with combined real and virtual robots. This 

capability adds to conventional simulation-based study to form an 

integrated measuring process. An example of robotic convoy system 

is presented together with metrics to measure the formation 

coherence of cooperative robotic system. Some preliminary 

simulation results are presented. 

KEYWORDS: Cooperative Robotic System, Virtual 

Environment, Robot-in-the-Loop Simulation, Robotic Convoy System 

1. INTRODUCTION 

Cooperative robotic systems couple computational 

intelligence to the physical world. These systems consist of 

multiple homogenous or heterogeneous robots that perceive 

the environment, make decisions, and carry out commands to 

affect the environment. Communication and cooperation is 

important for theses systems since their robots work as a 

collective team to finish common tasks. Several taxonomies 

and metrics have been defined to classify these systems. For 

example, Dudek, etc. [1] classifies robotic collectives along 

seven dimensions: size of the collective, communication 

range, communication topology, communication bandwidth, 

collective reconfigurability, processing ability of each 

collective unit, and collective composition. Balch [2] 

classifies the performance metric of multirobot tasks based on 

time, subject of action, resource limits, group movement, 

platform capabilities, etc. 

The increasing complexity of collective robotic systems 

calls for systematic methods as well as supporting 

environments to experiment, understand, and evaluate these 

systems. To serve this purpose, modeling and simulation 

technologies are frequently applied. With simulation-based 

methods, models of robots can be built and simulated. 

Different configurations can be easily applied to experiment 

and measure the performance of the system under 

development. To allow simulation of robotic systems that 

actively interact with an external environment, an 

environment model needs to be created. This environment 

model serves as a “virtual” environment to provide sensory 

input to robot models and to response to robots’ actuation. For 

example, a virtual environment for mobile robots simulation 

can have virtual obstacles that can be sensed by robot models, 

and it responds to robots’ movements by updating new 

sensory information to robot models. 

While robot models can be created and studied in a 

simulated environment, replacing some of the robot models 

with their real robot counterparts will bring simulation-based 

study one step closer to the reality and provides the flexibility 

to allows real robots to be experimented in a virtual 

environment. This capability of robot-in-the-loop simulation 

is especially useful for large-scale cooperative robotic 

systems whose complexity and scalability severely limit 

experimentation in a physical environment using all real 

robots. This paper presents an approach that allows a 

cooperative robotic system to be effectively evaluated in a 

virtual environment with combined real and virtual robots. 

This research is an extension to our previous work on a 

simulation-based software development methodology for 

cooperative robotic systems [3, 4]. This methodology 

supports “model continuity” so the simulation models in the 

design stage can be directly mapped to real robots to control 

the real robots in execution. It greatly eases the transition 

from simulation-based study to real robot implementation and 
increases the confidence that the final system implements the 

behavior as been developed. This research is based on the 

Discrete Event System Specification (DEVS) modeling and 

simulation framework [5]. 

The concept of virtual environment has been largely used 

by the technology of virtual reality (VR), which has been 

applied to various areas such as simulation of manufacturing 

plants, the planning of robotic workcells, and robot 

teleoperation systems. While the research of VR mainly deals 

with the interaction with human operators, our work focuses 

on the interaction between robots and the virtual environment. 

The following research work is related to our research from 

this perspective. Komoriya and Tani [6] developed a virtual 

environment that allows a single real robot to be 

experimented in a virtual environment. Wang [7] proposed a 

simulation environment that allow real and virtual robot to 

work together. The work of RAVE [8] developed a simulation 

environment that supports multiple mobile robotic systems. 

Our research extends these works by developing a welldefined architecture, an incremental development process, 

and by integrating experimental frames to measure 

cooperative robotic systems with combined real and virtual 

robots in a systematic way. 

This paper is organized as follows. Section 2 presents the 

virtual measuring environment from three aspects: the 

architecture, the measuring process, and the relationship to 

experimental frames. Section 3 describes a robotic convoy 

system as an illustrative example. The models of this system 

are first described, several metrics are then presented, and 

some preliminary simulation data is given. Section 4 

concludes this work and provides future research directions. 

2. A VIRTUAL EVALUATION 

ENVIRONMENT FOR ROBOTIC SYSTEMS 

The effectiveness of this simulation-based virtual evaluation 

environment is supported by a well-defined architecture, an 

incremental measuring process, and by integrating 

experimental frames to specify metrics for performance 

measurement. Next we present these three aspects 

respectively. 

2.1 Architecture of the Virtual Evaluation 

Environment 

In this research we view robotic systems as a particular form 

of real-time systems that monitor, respond to, or control, an 

external environment. This environment is connected to the 

computer system through sensors, actuators, and other inputoutput interfaces [9]. A robotic system from this point of 

view consists of sensors, actuators and the decision-making 

unit. A cooperative robotic system is composed of a 

collection of robots that communicate with each other and 

interact with an environment. 

This above description suggests the basic structure for a 

simulation-based virtual environment for robotic systems: an 

environment model, and a collection of robot models that 

include a decision making model, sensors, and actuators. The 

environment model represents the real environment within 

which the robotic system will be executed. It may include 

virtual obstacles, virtual robots, or any other entities that are 

useful for simulation-based study. It forms a virtual 

environment for the robots. The robot model represents the 

control software that governs the robot’s behavior. It also 

includes sensor and actuator interfaces to bridge the decisionmaking model and the simulation-based virtual environment. 

In our research, we clearly separate a robot’s decision-making 

unit, which is modeled as a DEVS atomic or coupled model, 

from the sensors and actuators that are modeled as DEVS 

Activities. Couplings can be added between DEVS Activities 

and the environment model thus messages can be passed 

between the decision-making model and the environment 

model through sensor/actuator Activities. 

virtual obstacle

virtual sensors

virtual environment

virtual counterpart 

of the real robot

virtual robots

Control

Model

HIL actuators

wireless 

communication

computer mobile robot

Figure 1: Architecture of robot-in-the-loop simulation 

The clear separation between robots’ decision-making 

model and sensor/actuator interfaces brings several 

advantages. First, it separates a robot’s decision-making from 

hardware interaction, thus making it easier for the designer to 

focus on the decision-making model, which is the main 

design interest. Secondly, the existence of a sensor/actuator 

interface layer makes it possible for the decision-making 

model to interact with different types of sensors/actuators, as 

long as the interface functions between them are maintained 

the same. Thus depending on different experimental and 

measuring objectives, a robot model can be equipped with 

different sensors/actuators to be experimented and measured. 

Our previous work [10] has taken advantage of these features 

to allow direct transferring of the decision-making models 

from simulation to real robots execution – a capability 

referred as model continuity. During simulation, the decisionmaking model interacts with a virtual environment through 

virtual sensors/actuators; during real execution, the real 

robots’ decision-making models interacts with a real 

environment through real sensor/actuator interfaces. An 

intermediate stage can also be developed to allow the 

decision-making model on a real robot to interact with the 

simulation-based virtual environment. We call this stage 

robot-in-the-loop simulation. It is achieved by configuring a 

real robot to use a combination of virtual and real 
sensors/actuators. For example, Figure 1 shows an 

experimental setup where one real mobile robot works 

together with a virtual environment. In this example, the 

mobile robot uses its virtual sensor to get sensory input from 

the virtual environment and uses its real motor interface to 

move the robot. As a result, this real robot moves in a 

physical field based the sensory input from a virtual 

environment. Within this virtual environment, the robot can 

“see” virtual obstacles and other virtual robots that are 

simulated by computers. This capability of robot-in-the-loop 

simulation brings simulation-based study one step closer to 

the reality. It also makes it possible to study and measure 

several real robots within a large robotic system that may 

include hundreds of robots. In this case, the rest of robots can 

be provided by the simulation-based virtual environment. 

One important issue for the robot-in-the-loop simulation 

is the synchronization between the real robots and the virtual 

environment. For example, in Figure 1, when the decisionmaking model issues a moving command, the real robot will 

move a distance in the physical environment. This change of 

position should also be updated by the virtual environment. 

For this purpose, each real robot has a virtual counterpart in 

the virtual environment. When a real robot moves, the 

position of its virtual counterpart will be updated. Thus the 

synchronization between the real robot and the virtual 

environment is actually the synchronization between the real 

robot and its virtual counterpart. Ideally, an independent 

monitoring system is needed to track the movement of the 

real robots and then inform the virtual environment to 

synchronize the distance and time of robots’ movements. In 

our current implementation, a set of HIL (hardware-in-theloop) sensors/actuators has been developed. These HIL 

sensors/actuators drive the real sensor/actuators, while in the 

meantime are coupled to the virtual environment thus 

messages can be sent to it. For the example shown in Figure 

1, the HIL motor drives the motor of the robots. In the 

meantime it catches the moveComplete signal returned from 

the motor and then sends a message to the virtual 

environment to update the position of its virtual counterpart. 

2.2 From Robot Model To Real Robot – An 

Incremental Measuring Process

Based on this virtual measuring environment, an incremental 

measuring process is developed. This process includes three 

steps and supports smooth transitions between them. These 

steps are measuring based on conventional simulation, 

measuring based on robot-in-the loop simulation, and 

measuring based on real robot execution. Figure 2 gives an 

example with two robots to illustrate this process. 

The first step is conventional simulation, where all 

components are models and simulated by fast-mode or realtime simulators in one computer. As shown in Figure 2(a), 

both robot models are equipped with virtual sensors and 

actuators to interact with the virtual environment. Couplings 

between two robots can also be added so they can send 

messages to each other. We note that this is the same setup as 

the simulations that most robotic research uses. It has the 

most flexibility as all components are models and different 

configurations can be easily applied to measure the system 

under development. 

Robot

Model

Robot

Model

Virtual Environment

Virtual 

Sensor 

Virtual

Actuator

Virtual 

Sensor 

Virtual

Actuator

Robot

Model

Real

Robot

Virtual Environment

Virtual 

Sensor 

Virtual

Actuator

Virtual 

Sensor 

HIL 

Actuator

Real

Robot

Real

Robot

Real Environment

Real 

Sensor 

Real

Actuator

Real 

Sensor 

Real

Actuator

(a) (b) (c)

Figure 2: An incremental measuring process 

The second step is robot-in-the-loop simulation where 

one or more real robots are measured and experimented 

within a virtual environment together with other virtual robots 

(robot models) that are simulated by computer. In this step, 

the virtual robots still use virtual sensors/actuators. However, 

depending on the measuring objectives, the real robots may 

have a combination of virtual and HIL sensors/actuators. For 

example, the real robot shown in Figure 2(b) uses a virtual 

sensor and a HIL actuator. The couplings between the two 

robots are maintained the same so the real and virtual robots 

can interact with each other in the same way as in the first 

step. However, the real commutation in this step happens 

across a wireless network, which is transparent to the robots. 

Since real robots are involved in the simulation, robot-in-theloop simulation has to run in a real-time fashion. 

The final step is the real system measurement, where real 

robots are measured in a real physical environment. These 

robots use real sensors and actuators. They communicate in 

the same way as the first two steps since the couplings 

between them are not changed through the process. The 

measurement of this step is from the reality, thus having the 

most fidelity. However, it is also most costly and time 

consuming among the three steps. 

This incremental measuring process brings simulationbased study closer and closer to the reality. As the process 

proceeds, the flexibility (easy to experiment different 

configurations) and productivity (time saving and cost saving) 

of the measurement decreases and the fidelity (loyal to the 

reality) of the measurement increases. 

2.3. Specify Measuring Metrics Using Experimental 

Frame 

An experimental frame is a specification of the conditions 

within which the system is observed or experimented [5]. In 

DEVS-based modeling and simulation framework, an 

experimental frame is realized as a system that interacts with 

the source system, or System Under Test (SUT), to obtain the 

data of interest under specified conditions. It consists of four 

major subsections: 

• input stimuli: specification of the class of admissible 

input time-dependent stimuli. This is the class from 
which individual samples will be drawn and injected into 

the model or system under test for particular 

experiments. 

• control: specification of the conditions under which the 

model or system will be initialized, continued under 

examination, and terminated. 

• metrics: specification of the data summarization 

functions and the measures to be employed to provide 

quantitative or qualitative measures of the input/output 

behavior of the model. Examples of such metrics are 

performance indices, goodness-of-fit criteria, and error 

accuracy bound. 

• analysis: specification of means by which the results of 

data collection in the frame will be analyzed to arrive at 

final conclusions. The data collected in a frame consists 

of pairs of input/output time functions. 

When an experimental frame is realized as a system to 

interact with the SUT (or its model), the four specifications 

become components of the driving system. For example, a 

generator of output time functions implements the class of 

input stimuli. 

Integrate experimental frames into the virtual measuring 

environment brings the advantage that measuring metrics can 

be formally specified. More research is on the way to 

integrate them in a structured way. In the meantime a set of 

measuring metrics is also under development for cooperative 

robotic systems. 

3. ROBOT CONVOY: A CASE STUDY 

EXAMPLE 

The presented virtual measuring environment has supported 

the development of a robotic convoy system. Below we 

briefly describe the model of this system, its measuring 

metrics, and some preliminary results that are collected from 

simulation-based study. We note that most results presented 

in this paper are collected from simulations that do not 

involve real robots. But in the next step we plan to measure 

the system using robot-in-the-loop simulation and expect to 

reach more interesting results. For example, we plan to use 

one real robot to run robot-in-the-loop simulation to check the 

convoy speed of this real robot and compare it with the data 

collected from the conventional simulation. Another result 

that we plan to check is to use two real robots neighboring to 

each other and then check the back robot’s position errors 

based on the position and direction of its front robot in the 

physical environment. 

3.1 System Description and System Model 

This robot convoy system consists of an indefinite number of 

robots, saying N robots (N>1). These robots are in a line 

formation where each robot (except the leader and the ender) 

has a front neighbor and a back neighbor. The robots used in 

this system are car type mobile robots with wireless 

communication capability. They can move forward/backward 

and rotate around the center, and have whisker sensors and 

infrared sensors. [11]. 

One of the basic goals of this convoy system is to 

maintain the coherence of the line formation and to 

synchronize robots’ movements. Synchronization means a 

robot cannot move forward if its “front” robot doesn’t move, 

and it has to wait if its “back” robot doesn’t catch up. To 

serve this purpose, synchronization messages are passed 

between a robot and its neighbors. To achieve coherence of 

the line formation, the moving parameters of a “front” robot 

are passed back. This allows the back robot to plan its own 

movement accordingly based on its front robot’s movement. 

The system has no global communication and coordination 

since we want to study how global behavior can be achieved 

using localized sensing and communication. 

Robot2

BReadyIn

FReadyIn

FReadyOut

BReadyOut

Robot3

BReadyIn

FReadyIn

FReadyOut

BReadyOut

FReadyOut

Robotn FReadyIn

BReadyIn Robot1 ... BReadyOut

... Robot2

BReadyIn

FReadyIn

FReadyOut

BReadyOut

Robot3

BReadyIn

FReadyIn

FReadyOut

BReadyOut

FReadyOut

Robotn FReadyIn

BReadyIn Robot1 ... BReadyOut

...

Figure 3: System model of the robotic convoy system 

Figure 3 shows the model of this system. As we can see, 

this model includes N models (each of them is a DEVS 

coupled model), which are corresponding to the N robots in 

the system. Each intermediate robot model has two input 

ports: FReadyIn, BReadyIn and two output ports: FReadyOut, 

BReadyOut. These ports are used to send and/or receive 

synchronization messages between robots and to pass moving 

parameters from a “front” robot to the “back” robot. The 

couplings between them are shown in Figure 3. 

During the convoy, the leader robot (Robot1 in Figure 3) 

decides the path of convoy. Meanwhile, it will turn around if 

its infrared sensors indicate that there are obstacles ahead. All 

other robots conduct movement based on their sensory input 

and the moving parameters passed back from their front 

robots. Specifically, a robot will “predict” where its front 

robot is and turn to that direction. It then moves forward or 

backward to “catch” its front robot. After that it may go 

through an “adjust” process to make sure that it does not lose 

its front robot. This adjust process is necessary because noise 

and variance exist during a movement so a robot will not 

reach the desired position and direction after the movement. 

During adjustment, a robot “scans” around until it finds its 

front robot. Then it sends out a synchronization message to 

“inform” its front and back neighbors. Thus robots actually go 

through a basic “turn—move—adjust—inform” routine. For 

example, a robot Ri-1 will turn angle αi-1 to the direction of its 

front robot Ri-2, move distance di-1 to “catch” its front robot, 
and then adjust itself with angle βi-1 to make sure it “sees” its 

front robot Ri-2. Figure 4 shows these moving parameters. 

δi

αi-1 αi

βi-1

a

di-1

di

D

Ri Ri-1

δi′

Ri-1′

Ri′

δi

αi-1 αi

βi-1

a

di-1

di

D

Ri Ri-1

δi′

Ri-1′

Ri′

Figure 4: Moving parameters for robots’ convoy 

After the adjustment, Ri-1 sends out a synchronization 

message to its neighbors. This synchronization message 

contains information of αi-1, di-1, and βi-1. Based on this 

information and its sensory data, Ri plans its movement. This 

is shown by Figure 4 and formulated by formula (1)-(3). 

Among these formulas, δi is the angle (direction) difference 

between Ri and Ri-1; a is the distance between robot Ri and Ri-1

and can be calculated from the robot’s infrared sensor data 

and the size of the robot. Specifically, the turning angle αi of 

Ri is calculated by formula (1); the moving distance di can be 

calculated from formula (2), where D is the desired distance 

between Ri and Ri-1. Then the new angle difference δi' 

between Ri and Ri-1 is updated by formula (3), where βi is the 

adjusting angle for Ri. We note that due to noise and variance, 

the δi' calculated from formula (3) will not be the exact angle 

difference between Ri and Ri-1. However, it seems that this 

error does not accumulate as time proceeds. 

*cos( )

*sin( )

1 1

1 1

i i i

i i i

i a d

d

tg

α δ

α δ

α

+ +

+ =

− −

− − (1) 

D d d

i

i i i

i − + = − −

α

α δ

sin

*sin( ) 1 1 (2) 

δ i = δ i +αi + βi −αi − βi

′ −1 −1 (3) 

The model of each robot is developed based on the 

subsumption architecture [12]. It has the Avoid model to 

avoid collisions with any objects; the Convoy model to 

control robot’s movement based on the rules as described 

above. It also has DEVE Activities to represent the 

sensor/actuator interfaces of the robot. A detailed description 

of a similar model can be found at [3]. 

Figure 5 shows the Environment model that we used for 

this example. This Environment model includes 

TimeManager models and the SpaceManager model. For 

each robot, there is a TimeManager corresponding to it. This 

TimeManager models the time for a robot to conduct a 

movement. The SpaceManager models the moving space, 

including the dimension, shape and location of the field and 

the objects inside the field. It also keeps track of robots’ (x,y)

positions and moving directions during simulation. Such 

tracking is needed to supply robots with the correct sensory 

data. To account for variability in the real motion, a random 

number generator provides a source of additive noise. Note 

that in this example we have ignored the dynamics of a 

movement as we treat each movement as an atomic action so 

the positions and directions of robots are updated discretely. 

move1 sensorData1

sensorDataN

startMove TimeManager1

Robot1 t1

SpaceManager

Robot1 (x, y)

RobotN (x, y)

Obstacles (x, y)

moveComplete1

moveN startMove TimeManagerN

RobotN tN

moveCompleteN

...

...

...

...

...

...

...

...

...

...

Figure 5: Environment model 

With all these models, simulation was run and a graphic 

user interface was developed to show robots’ movements. 

Figure 6 shows two snapshots of a robotic convoy system 

with 30 robots within a field surrounded by walls. As can be 

seen in this system, robots will not follow the exact track of 

the leader robot. However, they are able to follow their 

immediate front robots closely, thus forming a coherent team 

from a global point of view. Note that obstacles can also be 

easily added within the field. 

 (1) (2) 

Figure 6: Snapshot of robots in motion 

3.2 Measuring Metrics and Simulation Results 

A good set of measuring metrics is very important to study 

this robotic convoy system. This section describes several 

metrics that we have developed. These metrics are neither 

final nor complete. However, they serve as a starting point to 

analyze and measure this system. Some preliminary 

simulation results based on these metrics are also presented 

and analyzed. 

Convoy Speed and Number of Adjustment 

The convoy speed of the team and the number of 

adjustment for each robot are among the most obvious results 

that can be obtained from simulation-based study. Both them 

can be viewed as metrics for the system’s performance. In 

fact, these two metrics are correlated to each other: the larger 

the number of adjustment, the slower the convoy speed. Since 
robots move in a coordinated way, we define the convoy 

speed as the speed of the leader robot. This can be calculated 

by dividing the moving distance by the logic time of 

simulation. The number of adjustment can be obtained 

directly from each robot. 

Formation Coherence 

Due to noise and variance in reality, there exists 

difference between a robot’s real position, direction (angle) 

and its desired position and direction. This difference is 

affected by the variance of movement in real execution, 

which is modeled by adding noise into robot’s movement in 

simulation. On the other hand, even though variance exists, 

this system can still conduct the convoy with some level of 

formation coherence. This is because an “adjust process” has 

been implemented that allows robots to adjust their 

positions/directions based on the feedback from its infrared 

sensors. Apparently the level of formation coherence is 

affected by the variance of movement. If this variance is large 

enough, even though a adjust process exists, the system will 

eventually fail to maintain its formation coherence. 

To study this problem, we calculate each robot’s position 

errors under the effect of distance noise factor (DNF) and 

angle noise factor (ANF). These two factors are the ratio of 

the maximum distance variance and maximum angle variance 

as compared to the robot’s moving distance respectively. For 

example, if the angle noise factor is 0.1 and a robot moves 

forward 60, after its movement the robot will have maximum 

6 degrees variance from its desired direction. Once each 

robot’s position error is known, the average position error of 

the team can be derived. This average is an indicator for the 

convoy system’s formation coherence: the smaller the error is, 

the more coherent the convoy system is. Formula (4) – (7) 

shows how the average position error can be calculated. In 

these formulas, D is the desired distance between robots and 

N is the total number of robot. In case the formation 

coherence is broken, saying robot Ri lose itself, Ei(t) will 

increase continuously, making the average error E(t) increase 

too. Note that the desired position (xi-desired, yi-desired) of Ri is 

calculated from its front robot Ri-1’s position, not related to 

any specific formations. Thus systems with different line 

formation shapes may have the same position errors. 

2 2 E (t) (x (t) x (t)) ( y (t) y (t)) i = i − i−desired + i − i−desired (4) 

( ) ( ) *cos ( ) 1 1 x t x t D t i−desired = i− − θ i− (5) 

( ) ( ) * sin ( ) 1 1 y t y t D t i−desired = i− − θ i− (6) 

N

E t E t ∑ i = ( ) ( ) (7) 

Figure 7 shows the average poison error for a system 

with 30 robots, DNF=0.1, and ANF=0.08. The system starts 

with all robots at their desired positions. Thus as simulation 

proceeds, the position error increases from 0. It then reaches a 

“stable” stage where the position error oscillates around an 

average value (35.7 In this example). As we can see, in this 

system the position error does not accumulate over time. Thus 

we say that this system’s formation coherence is maintained. 

average position error with 30 robots

0

5

10

15

20

25

30

35

40

45

1

789

15772365315339414729551763057093788186699457

1024511033

simulation steps

position error

DNF=0.1, ANF=0.08

Figure 7: Average position error with 30 robots 

Sensitivity 

Since the formation coherence is affected by the noise 

factors, sensitivity analysis is useful to study if the system is 

robust to noise factors. To conduct sensitivity analysis, we run 

simulations with different noise factors and calculate the 

position errors. Figure 8 shows a system with 30 robots’ 

average position errors under the effect of three sets of DNF 

and ANF: set 1 has DNF = 0.04, ANF = 0.04; set 2 has DNF 

=0.1, ANF = 0.08; set 3 has DNF = 0.2, ANF = 0.1. For 

analysis purpose, we omit the “transient ” stage when the 

simulations start. 

Position errors vs. noise factors

20

25

30

35

40

45

1

564

1127169022532816337939424505506856316194675773207883844690099572

simulation steps

position errors

Series1

Series2

Series3

Figure 8: Average position errors vs. noise factors 

Figure 8 shows that different noise factors result in 

different error patterns. However, for this system, all three 

errors are still maintained within a boundary (they do not 

accumulate as time increases). By calculating the average of 

them, we have average1 = 35.1, average2 =35.7, and average3 

=36.6. From these data we can see that as the noise factor 

increases, the position error increases too. However, this 

change is insignificant as compared to change of the noise 

factors. Although more analysis is needed to reach any 

quantitative conclusion, we can say that this system is 

insensitive to the noise factors as long as these factors are 

within a safe boundary. This is because the system 

impalements an adjust process that allows robots to adjust 

themselves based on the feedback from their IR sensors. 
Scalability 

Scalability refers to the ability of a system to maintain its 

quality as the scale of the system increases. To study 

scalability, we change the number of robots and run 

simulation to see how that affects system’s average position 

error (average over number of robots and over time). Figure 9 

shows the position errors for the number of robots to be 10, 

20, 30, and 40 with DNF =0.1 and ANF =0.08. It shows that 

the average position error increases as the number of robot 

increases. If this trend holds true with more robots, the system 

is not scalable in the sense that it will eventually break as 

more robots are added into the system. 

Position error vs. number of robots

15

20

25

30

35

40

0 10 20 30 40 50

number of robots

position error

DNF=0.1, ANF=0.08

Figure 9: Average position errors vs. number of robots 

4. CONCLUSION

This paper presents a simulation-based virtual evaluation 

environment for cooperative robotic systems. This virtual 

environment allows a combination of real and virtual robots 

to work together for a system-wide study and measurement. 

An incremental measuring process is developed to transition 

simulation-based study closer to reality as the process 

proceeds. Based on this virtual environment, a robotic convoy 

system was developed and presented in this paper as an 

illustrative example. Coherence metrics for this system were 

defined and preliminary simulation results were discussed. 

We note that most results presented in this paper are 

collected from simulations that do not involve real robots. But 

in the next step we plan to measure the system using robot-inthe-loop simulation and expect to gather more interesting 

results. In the meantime, a set of more complete evaluation 

metrics is also under development for the robotic convoy 

systems presented in this paper. 

5. ACKNOWLEDGEMENT 

This research was supported by NSF grant DMI- 0122227, 

“DEVS as a Formal Framework for Scalable Enterprise 

Systems.” 

6. REFERENCE

[1] Dudek, G., Jenkin, M., and Milios, E., “A Taxonomy of 

Multirobot Systems”, Robot Teams, Edited by Balch, T., and 

Parker L.E., A K Peters, 2002 

[2] Balch, T., “Taxonomies of Multirobot Task and Reward”, 

Robot Teams, Edited by Balch, T., and Parker L.E., A K 

Peters, 2002 

[3] Hu, X., and Zeigler, B. P., “Model Continuity to Support 

Software Development for Distributed Robotic Systems: a 

Team Formation Example”, Journal of Intelligent & Robotic 

Systems, Theory & Application, Special Issue: Multiple and 

Distributed Cooperating Robots, pp. 71-87, January, 2004 

[4] Hu, X., and Zeigler, B.P., “A Simulation-based Software 

Development Methodology for Cooperative Real-time 

Intelligent Systems“, to appear in Annual of Complex Systems 

and Intelligence Science, World Scientific Publishing Co., 

2004 

[5] Zeigler, B.P., Kim, T.G., et al.. Theory of Modeling and 

Simulation. New York, NY, Academic Press, 2000. 

[6] Komoriya, K.; Tani, K., “Utilization of the virtual 

environment system for autonomous control of mobile 

robots”, Intelligent Motion Control, 1990. Proceedings of the 

IEEE International Workshop on, Volume: 2, 20-22 August 

1990 

[7] Wang. J.: Methodology and design principles for a generic 

simulation platform for distributed robotic system 

experimentation and development. Systems, Man, and 

Cybernetics, 1997. Computational Cybernetics and 

Simulation., 1997 IEEE International Conference on, Volume: 

2, 1997 Page(s): 1245 -1250 vol.2 

[8] Dixon, K.; Dolan, J.; Wesley Huang; Paredis, C.; Khosla, 

P., “RAVE: a real and virtual environment for multiple 

mobile robot systems”, Intelligent Robots and Systems, 1999. 

IROS '99. Proceedings. 1999 IEEE/RSJ International 

Conference on , Volume: 3 , 17-21 Oct. 1999 

[9] Shaw, S. C., Real-time Systems and Software, John Wiley 

& Sons, 2001 

[10] Hu, X., A Simulation-based Software Development 

Methodology for Distributed Real-time Systems, Dissertation, 

University of Arizona, 2003 

[11] Peipelman. J., N. Alvarez, K. Galinet, R. Olmos.: 498 A 

& B Technical Report. Department of Electrical and 

Computer Engineering, University of Arizona, 2002 

[12] Brooks, R. A., "A Robust Layered Control System For A 

Mobile Robot", IEEE Journal Of Robotics And Automation, 

RA-2, April. pp. 14-23, March 1986 
Behavioral Entropy in Human-Robot Interaction

M. A. Goodrich1, E. R. Boer2, J. W. Crandall1, R. W. Ricks1, and M. L. Quigley1

1 Computer Science Department 2 Erwin R. Boer Consulting

Brigham Young University San Diego, CA, USA

Provo, UT, USA

ABSTRACT

The ability to quickly and accurately measure how various design decisions affect human workload is an important need in human-robot interaction (HRI) and other

HMI domains. Although various techniques allow workload to be estimated, it is important to develop methods for obtaining workload estimates objectively and in

real-time without interfering with the normal operation

of human. In this paper, we develop behavioral entropy

as a technique for estimating human workload in HRI

domains. We develop relevant theory and present case

studies that help validate the power of behavioral entropy.

1 Introduction

In a recent article on useful metrics in human-robot interaction (HRI), Fong et al. identified the need to find

“nonintrusive measures of workload that can characterize operator stress in real-time” [3]. The importance of

having a real-time estimate requires an objective (rather

than subjective) measure of workload that is reliable and

applicable to many interfaces. The purpose of this paper is to present a technique, called behavioral entropy [6]

that measures human workload in HRI domains. This

metric efficiently utilizes operator activity to estimate

human workload.

A real-time measure of workload in HRI has several

possible applications.

• Design of adjustable autonomy systems. Intelligent interfaces could be used to identify high

workload situations, and the resulting information

could be used to adjust robot autonomy or alert

other humans to support the operator. This facilitates design of more efficient mixed-initiative systems [1] that follow principles of situation-adaptive

autonomy [4].

• Comparison of interfaces and autonomy

modes. Various HRI systems, including various interfaces and robot autonomy modes, could be compared over time. This ability to compare designs

over time allows not only comparison of average

workload, but also comparisons of peak workload,

minimum workload, and workload patterns.

• Diagnosis of causes of high workload. External

events that trigger high workload could be identified

and diagnosed. By associating a real-time estimate

of workload with external events, those events that

cause workload spikes could be identified. These

events might include environmental contingencies,

robot failures, interface issues, and so on.

• Design of Adaptive Systems. Interfaces or

robots that learn to support human activity could

be improved. Most HRI learning systems either

learn by direct teaching or learn by observing a human teleoperating a robot. These systems could

be augmented to include implicit human cues, such

as identifying robot behaviors that cause workload

spikes, and thereby improve interaction efficiency

through interface adaption.

The idea of behavioral entropy was developed in for

use in estimating driver workload in an automobile driving context. This first application restricted attention

to human activity as recorded in the steering wheel of a

vehicle and was called “steering entropy.” Subsequently,

Boer generalized this concept to general human activity,

and denoted the concept as behavioral entropy [6].

Behavioral entropy differs in a number of ways from

the three other primary methods for evaluating workload: physiological measurements, secondary task studies, and post hoc workload measurements (such as

NASATLX). Physiological measurements exploit the

strong correlation between human effort and the body’s

physical response. Such measures are objective and near

to real-time, but much work needs to be done to understand the precise nature of the correlation between effort

and response; this work includes developing signal processing techniques that rapidly and correctly separate

signal from noise. Secondary task studies allow diagnosis of human workload by measuring how performance

declines as other work is added. However, such measures are invasive and change the way the primary task
is performed. Post hoc measurements exploit a human’s

ability to express their perceived workload after the fact.

Such measures are important because they allow a human to be able to state how they perceived their experiences, but they are subject to many psychological biases,

such as recency effects. Moreover, they are not real-time.

Behavioral entropy exploits patterns observed in human activity within an HRI context. Generally speaking, when intelligent operators perform a practiced skill

under conditions of good information, they use an anticipatory control strategy. This means that they are

able to predict the consequences of their actions or inactions, and select efficient behaviors that alter these

consequences. When human operators are under conditions of high workload or other form of degraded performance, they anticipate less and react more and, as a

result, their action selection tends to be more exaggerated. Anticipatory behaviors tend to be more smooth

with less dramatic magnitudes and less frequent changes

than reactive behaviors. Behavioral entropy is sensitive

to this difference between reactive and anticipatory behaviors.

This paper is organized as follows. We first review

and develop the key concepts associated with behavioral

entropy. We then present three case studies that utilize

behavioral entropy in HRI-related domains. The first

two case studies help establish the hypothesis that average behavioral entropy is a useful and objective metric

for comparing design decisions. The third case study

helps illustrate that behavioral entropy can be used in

real-time. We conclude by presenting future work with

an emphasis on work needed to allow behavioral entropy

to be used in broad-reaching HRI studies.

2 Behavioral Entropy

Behavioral entropy estimates workload by first observing patterns of human activity under normal conditions,

and then noting deviations from these patterns. Consider, for example, how a human might teleoperate a

robot via a joystick under laboratory conditions (good

communications, alert operator, etc.). Under these ideal

conditions, joystick activity follows observable patterns.

Such patterns of activity can be captured in a model of

activity. A well-known phenomena associated with modelling is that simple models often explain most activity,

but extending these models to explain all activity often

makes the models grow exponentially in their complexity. This is true in human-robot interaction domains as

well. For example, much of what is done with the joystick under teleoperation can be described with simple

ARMA models [5], but modelling all joystick activity

requires very sophisticated models.

Norbert Wiener once said, “It is my thesis that the

physical functioning of the living individual and the operation of some of the newer communication machines

are precisely parallel in their analogous attempts to control entropy through feedback” [8]. Through repeated interactions with robot or interface systems, humans build

an understanding of various effects and relationships.

Perhaps most importantly, they build an understanding of (a) the effect of their actions on the systems and

(b) the dynamics of the environment.

Such an understanding translates into an efficient interaction. To paraphrase Wiener, people work to reduce entropy so skilled behavior minimizes entropy. This

manifests itself in human behavior that is anticipatory,

of the lowest possible bandwidth, and of the lowest possible magnitude. Such behavior lends itself to modelling

and prediction.

2.1 Modelling

Suppose that we identify a simple model that describes

how the operator uses the input device to a human-robot

interface. (Such input devices can include a joystick,

mouse, stylus, etc.) Formally, let xt denote the state of

the world at time t and let at denote operator activity

at time t. A model M, denoted by,

M : Xt × Xt−1 ×. . .× X0 ×At ×At−1 ×. . .×A0 → At+1

can be used to predict operator activity at time t + 1,

aˆt+1 = M(xt, xt−1, . . . , x0; at, at−1, . . . , a0),

where the ˆa indicates a prediction. Given this model we

can generate a prediction of what we think the operator

will do next.

If we adopt Wiener’s hypothesis that people work to

control entropy, then we can believe the hypothesis that

people’s behavior patterns have lower magnitude, have

lower bandwidth, and are anticipatory when good information is present and the task is well practiced. If so,

then low frequency components of their observed activities represent the anticipatory aspects of their behavior.

Consequently, we should be able to identify a model of

this behavior.

Their are several possible choices for these models. We

could use general linear models, such as ARMA or statespace models, but in the interest of simplicity we restrict attention to only one type of model in this paper1

:

a Taylor series expansion. The Taylor series expansion

supposes that behavior is a smooth function of past activities, and then uses the first derivatives to model the

key elements of this function.

1Note that it might sometimes be better to use a sample and

hold model to predict joystick movement because joystick operation, under some conditions, tends to be “bang-bang.” This is left

as an area for future work.
2.2 Model Errors

Clearly, a model will not correctly predict all operator

activity. Let et = ˆat − at denote the error in this prediction. The statistical properties of this error are useful in

estimating operator workload. To illustrate this, suppose

that the prediction error sequence, et, has been observed

for 0 ≤ t ≤ N. Given this sequence, {e0, e1, . . . , eN }, we

can create a histogram of prediction errors. By normalizing this histogram, we create a probability mass function

that is a non-parametric estimate of the prediction error

density function. Let pE(e;t) denote this estimate of the

prediction error density function.

The key idea behind using behavioral entropy is to

look at the type of information that exists in the prediction error density function. More precisely, we will

look at the information present in the prediction error

density functions under two conditions. If one condition

is produced under circumstances that allow better anticipatory control than the second condition, then operator

activity under the first condition should be more predictable. In other words, there will be less information

in the prediction error density function. Since good interfaces and autonomy modes support operators in their

desire to minimize entropy, good designs should have

more predictable behaviors. To better understand how

to describe the information available in the prediction error density function, it is useful to review the relationship

between creating a model and the notion of information.

2.3 Models and Information

One way to interpret a model of a phenomena is as a

mechanism that gives you information about the phenomena. In this sense, we use the term “information”

in the information theoretic sense as the number of bits

required to describe the phenomena. If the model is

very good, then deviations from the model predictions

likely arise from randomness; if the model is poor, then

deviations from the model predictions likely arise from

structured aspects of the phenomena that are not captured in the model. For example, consider a phenomena

where two variables are related to each other by a cosine

function. If we create a linear model for this sinusoidal

relationship, then deviations from the model predictions

arise from the fact that the underlying phenomena is a

sinusoid and not a line. If, by contrast, we create a sinusoid model for this relationship, then deviations from

model predictions arise from random perturbations in

the relationship.

We can use this relationship between model predictions and information to create a mechanism that identifies when activity is no longer ascribed to the phenomena

encoded in the model. In other words, we can use the

prediction error density function to detect when things

are different from what we predict and therefore detect

when the phenomena is behaving oddly. Since predictions are subject to random error, we are actually going to use the prediction error density function to detect when things are different enough to conclude that

the observed phenomena is not consistent with what was

predicted.

Consider the amount of information available in the

prediction error density. Under ideal conditions (e.g.,

laboratory setting, alert human, no interruptions) the

prediction error density, pE(e;t), has a certain amount

of information in it. This information is attributable to

random noise and to small unmodelled aspects of the

pattern of human activity. If conditions of high workload occur, then the pattern of human activity changes

and so does the resulting prediction error density. By

comparing the amount of information present in the prediction error density function under ideal conditions to

the information present under loaded conditions, we can

detect when these loaded conditions have occurred.

For example, consider the problem of teleoperating a

robot via a joystick. We can create a simple model for

how the joystick moves under ideal conditions and measure the information in the corresponding prediction error density. When the task suddenly becomes more difficult, operator activity tends to become more erratic and

more pronounced. Instead of seeing small changes in the

joystick position made relatively infrequently, large and

rapid changes in joystick position are more frequently

observed. If we were to compare the prediction error

density under ideal conditions with the density under

the loaded conditions, we would see that the density under loaded conditions is much more spread out; this is

illustrated in Figure 1. This increased density spread in-

-0.2 -0.1 0 0.1 0.2

0

5000

10000

15000 Interface 1

Interface 2

Figure 1: Prediction error histograms under two workload conditions: nominal and loaded.

dicates that there is information in the system not captured by the model; it indicates that the operator is doing more than we predicted. Such things can occur, for

example, when an operator overcompensates after hav-
ing attention diverted or when an operator is confused

because information is presented poorly.

2.4 Model Information and Prediction

Error Entropy

To create a metric that represents this change in prediction error density, we return to the information theoretic

interpretation of the model. We use entropy, H(E;t),

defined as H(E;t) = −

P

e∈E

pE(e;t) log pE(e;t), as the

measure of information available in the prediction error

density. If we identify baseline entropy using ideal conditions then we can detect periods of high workload by

comparing H(E;t) against the baseline entropy. Similarly, if we can identify entropy under one HRI system

design, then we can compare this entropy with another

design to help determine which design better supports

the human.

We refer to H(E;t) as behavioral entropy, indicating

that it is the amount of information present in a human’s

behavior that was not captured by a model. Experiments

in automobile driving indicate that this objective measure of entropy correlates well with subjective measures

of workload [6].

2.5 Segue

In the remainder of this paper, we present three case

studies that use behavioral entropy to perform various HRI-related tasks.In the case studies, we will first

present the goal of the experiment, describe what the

operator was asked to do, discuss characteristics of the

environment and the interface, present the model used

to predict operator activity, and present what we use as

a baseline. The first two studies use average behavioral

entropy and lend support to the thesis that behavioral

entropy discriminates between good and bad operating

conditions. The third case study uses a real-time version of behavioral entropy to learn proper force feedback;

this case study uses a reinforcement learning technique

to show that real-time estimates of behavioral entropy

are informative.

3 Case Study 1: Comparing Usability of Two Teleoperation

Schemes

In the first case study, behavioral entropy was used to

compare two different robot autonomy modes to determine which autonomy mode was easier for humans to

use. The hypothesis is that differences in behavioral entropy correlate well with other measures of performance

and are therefore useful in comparing different robot autonomy modes. We compute the prediction error density function using a prediction error sequence from the

entire experiment, and compare the entropy of this density function with other performance measures under two

robot autonomy modes.

Subjects were asked to drive a robot around the

top floor of the Computer Science Department at

Brigham Young University using two different autonomy modes: manual teleoperation and shared-control

teleoperation [2]. In addition to driving the robot with

their right hand (with a joystick), the users were asked

to answer multiple choice (two-digit) addition and subtraction problems with their left hand. This experiment

setup is illustrated in Figure 2. Subjects were told to

guide the robot through the hallways as quickly as possible while answering as many math questions as possible.

The video feed from the robot’s onboard camera was displayed on the same screen as the math problems. In this

case study, entropy calculations were taken of joystick

movements. Only the angle (not the magnitude) from

the joystick input was used to calculate entropy.

98

+33

A) 14

B) 123

C) 131

D) 56

Figure 2: Interface used to compare the two autonomy

modes.

3.1 Methods

A second-order Taylor series model of operator behavior

was used. This means that the operator activity at time

t, at, was determined using observations of activity at

times t − 3 through t − 1 (i.e., using at−1, at−2, and

at−3). In this experiment, only joystick angle was used,

and it is a reasonable assumption that if the operator is

using angle a at times t − 3 through t − 1 then they will

likely use this same angle at time t.

An important aspect computing entropy is selecting

how to reliably create a discretized probability mass

function from histogram data. In this experiment, a single operator guided the robot through the maze using

the shared control autonomy mode without performing

the secondary task. The history of joystick angles was
recorded, and the prediction error histogram was created. This histogram was discretized into 9 unequally

spaced bins.

The bins were created using the following procedure.

Using the resulting baseline prediction error density, we

identify the parameter, α, which encapsulates 90% of

the data, P r(−α <= error <= α) = 0.90. This value

of α is used to classify each angle, or the error from the

predicted angle, into nine bins,

{(−∞, −5α), [−5α, −2.5α), [−2.5α, −α), . . .

[−α, −0.5α), [−0.5α, 0.5α],(5α, ∞)}.

Since the bins were created from a single operator,

this implementation of behavioral entropy is not sensitive enough to allow comparisons between individuals.

Simply put, these values will be slightly different for

each individual under ideal circumstances so the entropy

computed from these values will differ under loaded conditions. As a result, entropy calculations should not be

used to compare two individuals. However, since the

same model and binning scheme were used under the

two experimental conditions (with shared control and

with direct control), it is possible to compare entropy

for a given individual on the two different tasks.

3.2 Results

This experiment was performed in the real world and in

a simulated world. Various results are shown for these

case studies. Table 1 and 2 show the results from experiments in real and simulated worlds, respectively. In the

tables, high values are good and low values are bad, with

the exception of the entropy measurement which is reversed. In the tables, Neglect indicates the percentage of

time that the operator spent doing arithmetic problems,

Performance indicates how efficiently the primary task

was completed as a percentage of the maximum possible

performance, # per min indicate the number of arithmetic problems that were attempted per minute, and

% Correct indicates what percentage of the attempted

arithmetic problems were answered correctly by the subject.

For all measurements in both tables, subjects tended

to do better using shared control than using direct control. Behavioral entropy is consistent with these other

measurements since the highest entropy measure for

shared control is lower than the lowest entropy measure

for manual control. Also, entropy is highly correlated

with performance (lower entropy corresponds to higher

performance) and the amount of time the human “neglected” (i.e., did math problems) the robot (lower entropy means, generally, more neglect). There also appears to be correlation between secondary task proficiency and entropy.

Shared-Control Results

Participant A B C D Ave.

% Neglect 51% 67% 46% 63% 57%

% Performance 77% 96% 81% 86% 85%

# per min. 9.5 18.9 8.9 10.6 12.0

% Correct 74% 98% 94% 66% 83%

Entropy 0.56 0.42 0.51 0.35 0.46

Direct-Control Results

Participant A B C D Ave.

% Neglect 36% 31% 22% 62% 38%

% Performance 57% 76% 58% 60% 63%

# per min. 6.4 9.1 3.9 9.8 7.3

% Correct 72% 85% 79% 61% 74%

Entropy 0.72 0.79 0.67 0.63 0.70

Table 1: Results from the experiment in the real world.

The key to understanding how this data supports the

use of entropy as a measure of workload lies in the dual

task nature of the experiment. Adopting a limited resource model for cognitive information processing [7], we

can assume that motivated subjects spend most of their

cognitive effort either guiding the robot or solving math

problems. This assumption is supported by the observation that the shared control autonomy mode was easier

to use and freed subjects to spend more time solving

math problems.

In the absence of a secondary task, it is reasonable

to assume that performances using the two autonomy

modes would have been closer. The presence of the secondary task provided stronger evidence that the shared

control autonomy mode was easier to use, but this secondary task also changed the nature of the task that the

operator was asked to perform.

Behavioral entropy data was consistent with the conclusion that direct control required more work. Since

behavioral entropy only required observations of operator activity (and did not require an intrusive secondary

task), we could have used behavioral entropy without

the secondary task to conclude that the shared control

autonomy mode was easier to use than the direct control

autonomy mode.

In summary, since higher entropy values occurred under direct control, the evidence supports the hypothesis

that entropy allows us to identify which autonomy mode

imposes higher human workload.

4 Case Study 2: Comparing the

Usability of Two Interfaces

In the previous case study, we used behavioral entropy to

measure the differences between two autonomy modes.

In this case study, we determine whether entropy is a

reliable method for determining which of two interfaces

provides better support for robot teleoperation.
Shared-Control Results

Participant A B C D E F G Ave.

% Neglect 74% 72% 77% 61% 73% 72% 74% 72%

% Performance 97% 88% 94% 98% 85% 92% 97% 93%

# per min. 12.0 12.4 10.3 12.1 13.8 16.3 15.8 13.2

% Correct 71% 63% 39% 94% 85% 88% 78% 74%

Entropy 0.37 0.49 0.45 0.32 0.39 0.55 0.29 0.41

Direct-Control Results

Participant A B C D E F G Ave.

% Neglect 65% 70% 70% 34% 70% 68% 73% 64%

% Performance 83% 74% 96% 96% 88% 75% 81% 84%

# per min. 10.2 12.5 9.8 6.4 11.5 12.7 13.4 10.9

% Correct 57% 63% 38% 79% 71% 88% 77% 67%

Entropy 0.68 0.77 0.69 0.57 0.66 0.72 0.67 0.68

Table 2: Results from the simulated world.

Figure 3: Interface that displays sensor readings side by

side.

Figure 4: Interface that integrates sensor readings into

perspective view.

The two interfaces are shown in Figures 3-4. The first

interface displays, from left to right, laser range finger

readings, video, and sonar in a side by side format. The

second interface integrates these three sensor readings in

a pseudo-perspective view, with a representation of the

robot displayed in this view.

We conducted a series of experiments to compare the

two interfaces. In a balanced experiment design with a

randomized schedule, subjects teleoperate a simulated

robot through three mazes while performing a memory

task where they must remember five images. After completing the maze, subjects complete a memory test by selecting the images they saw before from a list and putting

the images in order.

4.1 Methods

As in the previous case study, the model of joystick angles was based on a Taylor series. Given studies on human control characteristics, we used a sample interval of

150ms and averaged all joystick angles within a 150ms

window as our sample. Given the series of joystick angles, we created the prediction error density using the

difference between the predicted value and the observed

value. From the set of prediction error densities (one for

each maze and for each interface), it is necessary to identify a baseline density from which bins are created. We

did this by having each subject guide the robot through

one maze without performing the memory task using

the side by side interface. Prediction errors from this

entire data set were then used to create the bins used to

determine entropy using the technique described in the

previous case study.

4.2 Results

The following data were collected for 32 subjects: time

to guide a robot through a maze, behavioral entropy, average velocity, number of collisions, and performance on

a memory task. (Most likely, the memory tasks were not

hard enough because about 70% of the test subjects aced

the memory task.) With the exception of the memory

task, for which we did not get any meaningful data, all

of these measures demonstrate that the new interface is

effective for helping people control a robot.

Figure 5 summarizes the data, and shows that the side

by side interface is inferior to the perspective interface

for each measurement. These findings support the conclusion that behavioral entropy is a useful measure for

determining when one interface is more difficult to use

than another. Moreover, the data is strongly supported
Figure 5: A comparison of the performance metrics averaged over all subjects and all test worlds.

by the number of collisions experienced; the number of

collisions using the side by side display were more than

doubled the number of collisions using the perspective

display.

The perspective interface tends to be easier to use because it helps people predict where the robot will be

heading and updates this information frequently. The

side by side interface requires people to do their own

prediction and only updates sensor values when new information is received. Using the side by side interface

caused people to change their control input when new information was received from the robot. This causes the

position of the joystick to be somewhat erratic and jump

from position to position. People driving the perspective

interface often make more frequent but less dramatic corrections. This can be attributed to lower workloads or

finer control.

5 Case Study 3: Using Behavioral Entropy to Build an Interface

In this section, we present a case study that uses a realtime estimate of behavioral entropy as a major factor in

constructing an estimate of driver workload. This workload estimate is then used to learn haptic control policies

for an accelerator pedal that increase the safety of the

driver without significantly increasing workload. We use

the ability of reinforcement learning to detect patterns in

stochastic reinforcers to support the conclusion that the

real-time estimate of behavioral entropy contains useful

information about when people have workload spikes.

5.1 Methods

In the experiment, subjects followed an erratic lead vehicle with and without the learned force profile. During the

experiment, subjects solved two-digit arithmetic problems that appeared on the simulator by pushing buttons

on the steering wheel.

We trained an artificial agent using satisficing Qlearning, a dual attribute version of the standard Qlearning algorithm, to minimize workload while preserving safety. This was done by creating the following dichotomous goals: Goal #1: Don’t allow the vehicle to

experience a crash or a near-crash. Goal #2: Reduce

driver workload as much as possible. Clearly, these two

goals are in conflict with each other whenever the vehicle is in a non-trivial situation. Goal #1 was realized by

penalizing policies that lead to a collision or near collision. Goal #2 was realized by only rewarding actions

that induced a low user workload. Both behavioral entropy and impedance (i.e. the extent to which interface

actions directly opposed driver actions) were used to estimate driver workload and determine whether actions

produced a workload low enough to be rewarded.

5.2 Results

A control policy for a force-feedback gas pedal was

learned using the methodology described above. Entropy of the accelerator pedal position was calculated in

real-time and combined with instantaneous impedance

to form an estimate of driver workload. This estimate of

driver workload was compared against baseline driving

and empirically chosen thresholds to determine whether

an action induced too much workload to be rewarded.

The learning algorithm was trained during ten minutes

of exploratory driving by a single operator who allowed

several rear-end collisions to occur in order to propagate penalty data throughout the state space. The agent

learned to balance driver workload with expected risk,

applying forces to the pedal only in states where experience demonstrated it to be useful.

Test subjects responded enthusiastically to this haptic support. Pedal entropy remained similar to drivers

that were in unassisted trials, but the overall safety (as

measured by time spent with time to contact less than

0.7 seconds) was reduced by 45%. Using high entropy to

prevent rewarding an action during the training period

was very helpful in this context, as the agent learned a

control policy that informed the user of danger without

significantly increasing overall entropy. This evidence

supports the conclusion that the online estimate of behavioral entropy contained useful information about the

workload experienced by a distracted driver with and

without force feedback support. This evidence is bolstered by plotting the prediction error density functions
and noting that the density corresponding to no forces

is shorter and fatter than the other; these densities were

shown in Figure 1.

6 Discussion and Future Work

In this paper, we presented three case studies that

demonstrated how behavioral entropy can be used in

HRI studies. These case studies showed that behavioral

entropy reliably predicted workload and correlated well

with other measures of human performance. The third

case study also demonstrated how a real-time estimate of

behavioral entropy provided useful information to a machine learning algorithm; this algorithm decreased the

number of near collisions in a driving simulator without

increasing subjective workload.

Two areas of future work need to be explored before

entropy can be used widely. First, a guide for selecting

parameters in the entropy computation algorithm need

to be identified. These parameters include what models should be chosen, how model parameters should be

chosen, how binning should be performed, and how a

window size for real-time entropy estimates should be

selected.

Second, the relationship between entropy and other

human factors measures should be better established.

This includes researching how average entropy or its variations (e.g., peak entropy, minimum entropy) correlate

with, for example, trust, neglect tolerance, interface efficiency, and so on.

Acknowledgements

The authors would like to thank DARPA (under contract

#NBCH1020013) and Nissan Motor Company for their

partial support of this work.

References

[1] David J. Bruemmer, Julie L. Marble, David D. Dudenhoeffer, Matthew O. Anderson, and Mark D.

McKay. Mixed-initiative control for remote characterization of hazardous environments. In HICSS,

2003.

[2] J. W. Crandall and M. A. Goodrich. Characterizing

efficiency of human robot interaction: A case study

of shared-control teleoperation. In Proceedings of the

2002 IEEE /RSJ International Conference on Intelligent Robots and Systems, Luasanne, Switzerland,

2002.

[3] T. Fong, D. Kaber, M. Lewis, J. Sholtz, A. Schultz,

and A. Steinfeld. Common metrics for human-robot

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[4] T. Inagaki and K. Inoue. Adaptive choice of a safety

management scheme upon an alarm under supervisory control of a large-complex system. Reliability

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[5] L. Ljung. System Identification: Theory for the User.

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[6] O. Nakayama, T. Futami, T. Nakamura, and E. R.

Boer. Development of a steering entropy method for

evaluating driver workload. In SAE Technical Paper

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March 1-4, 1999.

[7] C. D. Wickens and J. G. Hollands. Engineering

Psychology and Human Performance. Prentice Hall,

third edition, 2000.

[8] N. Wiener. The Human Use of Human Beings: Cybernetics and Society. Free Association Books, London, 1989.
Evaluation of Human-robot Interaction in the NIST 

Reference Search and Rescue Test Arenas 

Jean Scholtz, Brian Antonishek, and Jeff Young 

National Institute of Standards and Technology 

Abstract 

In this paper we discuss studies we have been conducting on human-robot interaction (HRI) during the 

Urban Search and Rescue (USAR) competitions in the NIST Reference Test Arena. We discuss some of 

the analyses we have already done on the data we have collected and present the guidelines we have 

produced based on these studies. We discuss future plans for augmenting USAR competitions to 

specifically compare different methods of HRI. 

Introduction 

The ultimate evaluation of how humans and robots interact is the measure of their combined performance. 

In search and rescue the human-robot team has two goals: to locate victims and to provide accurate 

information about their location and their alertness state to human rescuers. These goals need to be 

achieved under a number of constraints. Teams need to operate for extended periods of time; the number 

of personnel used in the operation should be limited due to the dangerous nature of the operation; and the 

tasks need to be accomplished quickly to maximize the lives that can be saved [2]. Many human-robot 

search and rescue teams have participated in Urban Search and Rescue (USAR) competitions in the NIST 

test arenas [7,8]. The overall scoring for these competitions emphasizes these goals and constraints. 

Although scoring varies from year to year, the teams are rewarded for locating victims in a timely fashion, 

accurately assessing their condition, and providing good maps for rescue workers. Teams are penalized for 

causing further damage to the collapsed structure. Teams requiring multiple operators for individual robots 

are also penalized. 

Good human-robot interaction (HRI) contributes heavily to a team’s overall score. However, there are a 

number of other contributing factors as well, including the mobility of the robot, the skill of the operator, 

the robustness of the hardware, software, and communications, and the sensory perception provided. We 

are interested in evaluating the various user interfaces to determine what information and information 

presentation contributes to the overall performance of the system. 

Pros and Cons of Using the USAR Competitions for HRI 

Evaluation 

The primary benefit of using these competitions for studying HRI evaluation is that the competitors provide 

many more ideas for user interfaces than we, as researchers, could possibly prototype and test. 

The limitations are that we can only study the operator role [11]. The operators in the competitions are 

expert users, i.e., robotics researchers. We are not allowed to interfere with the competition environment 

which means that we cannot collect think-aloud or talk-aloud protocols [5,6] from the operators. It is 

difficult to interview the operators after their runs as they are busy getting ready for their next round. 

Moreover, the teams come from allover the world and there are language barriers to overcome. The user 

interfaces and the robots are dynamic. The teams make changes during the competitions. Different robots 

are used; different sensors are used; different teammates take turns at being the operator. 
In spite of the limitations, these competitions provide a rich source of data in a reasonable USAR 

simulation. 

Data Collection 

We have collected data at six major competitions starting in 2002. We collect video data of the user 

interface, the operator, and the robot as it moves through the arena. In addition we collect information 

about the robot’s path and coverage of the arenas. We also have access to the overall performance scores 

including penalties occurred. 

We typically tap into the video output of the operator control unit (OCU) and direct this to a scan converter 

which sends the converted output to a video recorder for later analysis. As the setup time for teams to get 

ready for their rounds is between 10 and 15 minutes, data collection setup has to be quick and flawless. 

Prior to the initial rounds, we test out the data collection equipment with each team who agrees to 

participate in our study. We make sure that all the video is time stamped so that we can easily move 

between the operator view of the user interface and ground truth as represented by the robot moving in the 

arena during analysis. It is difficult to tape the movement of the robot in the arena, as portions of the arenas 

are covered. Debris and multiple levels in the arenas make it difficult to see the robot at all times without 

being physically in the arena. We try to capture data from outside of the arena as our presence can cause 

the sensors on the robot to mistakenly identify us as victims or unintentionally point out possible paths 

through the debris. Figure 1 shows three different sections of the Robocup 2004 NIST test arenas. 

Figure 1: NIST Test Arenas at the Robocup USAR 2004 Competition 

Analysis of Data 

We have completed analysis of two sets of data at this point in time. Our initial data analysis was 

completed on data collected at the 2002 USAR competition at the American Association of Artificial 

Intelligence [14]. We collected data from all the teams in the competitions but we coded only data from the 

four top ranking teams. We used the data from the semifinals and finals. We were interested in looking at 

how the overall performance correlated with a finer analysis of performance. We looked at the video tapes 

and coded the amount of time each team spent in navigation or monitoring navigation, in identifying 

victims, in logistics, and in failures. Table 1 contains the definitions of these terms. 
Table 1: Definitions of Coded Activities 

Activity Coded Definition 

Navigation or monitoring navigation This activity was coded when operators were 

teleoperating a robot, or in the case of semiautonomous robots, when the operator was issuing 

navigation commands and watching the user 

interface to assess how the robot was moving. 

Victim identification We coded this activity when the operator thought he 

had sensed a victim and moved closer or used other 

sensors to assess the status of the victim. 

Logistics Activities such as starting up another robot were 

coded as logistics. 

Failures Hardware, software, and communications dropouts 

were coded as failures. 

Table 2 shows the percentage of times the four teams spent in these activities. Note that we were only able 

to code two of the three runs due to issues with the data collection mechanism. The total time is given in 

minutes. Each team was allocated 15 minutes for their runs. It was difficult to actually coordinate with the 

competition officials to know the actual start and stop times and, in one case, we lost some time due to a 

data collection issue. Note that the percentages do always add up to 100%. This is basically due to 

rounding areas in calculating times. 

Table 2: How teams spent their time 

 % Time 

Run Total 

Time 

(min) 

Navigation/ 

Monitoring 

Navigation 

Victim ID Failure Logistics 

Team A 1 

3 

10:39 

14:45 

46 

62 

51 

18 

0 

19 

3 

1 

Team B 1 

3 

14:33 

16:42 

81 

77 

19 

23 

0 

0 

0 

0 

Team C 1 

3 

13:26 

14:39 

59 

69 

23 

12 

17 

18 

0 

0 

Team D 1 

3 

15:12 

13:30 

55 

87 

32 

4 

0 

0 

12 

9 

We found that teams using some sort of automatic mapping were more successful in navigating the arenas. 

Operators who had to keep maps in their heads became confused about where they were at times. We 

looked at the penalties incurred by the teams and found instances where the operators were unaware of the 

surroundings of the robots or the status of the robots. In particular, few robots in this particular competition 

had a view of what was behind them. In situations where the operator was forced to back up or to make a 

series of tight turns this resulted in penalties for bumping into walls or victims. 

In our analysis of a second set of data collected at Robocup 2003, we looked at issues of awareness [9]. 

Burke [1] identified situation awareness (SA) as a major component needed for effective human-robot 

performance. Scholtz[10] has modified Endsley’s SAGAT [4] methodology for measuring the SA 

provided by supervisory interfaces for semi-automonous driving vehicles. Scholtz also analyzed the time 

needed for operator acquisition of SA in two types of terrains [12, 13]. In this analysis we used a 

modification of awareness tailored to HRI [3]. 
If we consider teams consisting of humans and robots, we can define 5 types of awareness: 

• Human-robot awareness 

• Robot – human awareness 

• Human-human awareness 

• Robot – robot awareness 

• Humans’ overall mission awareness 

In the majority of teams competing in the USAR Test Arenas, we are able to evaluate only human-robot 

awareness. That is, does the human have knowledge of the location, status, and behavior of the robot? We 

find few teams that have multiple robots with any collaboration capabilities (robot-robot awareness) or use 

multiple operators (human-human awareness). Moreover, the current generation of robots in these 

competitions has no awareness of the operators’ status (robot-human awareness). 

We used an indirect means of assessing human-robot awareness as we are not able to intervene and ask the 

operator to verbally describe any given situation. We coded critical incidents observed in the video tapes 

of the robot moving in the arena. Critical incidents are defined as a situation where the robot was in a 

position that could potentially be harmful to the robot, the environment, a victim, or the mission. 

Originally, we had intended to code critical incidents that were “avoided”, such as when the robot was able 

to move through an extremely tight space without causing any damage. However, we found that we were 

unable to do this consistently. We were able to consistently locate and code critical incidents that had a 

negative outcome, e.g. the robot bumped into a wall. We classified the critical awareness incidents into one 

of five categories: global navigation, local navigation, victim identification, obstacle extraction, vehicle 

state. Obstacle encounter was coded when the robot had actually run into an obstacle and had to perform 

maneuvers to free itself. Vehicle state awareness was coded when the operator did not realize that the robot 

was in other than a normal state, e.g. tipped over. In the runs we coded, we found evidence of critical 

incidents only in the categories of local navigation, obstacle extraction, and vehicle state. We did see 

evidence of the other types of critical incidents but these were not in the actual runs selected for coding (the 

semifinals and finals). Table 3 shows the numbers of critical incidents occurring for the three teams 

analyzed. These three teams were selected for analysis as they placed in the final round of the competition. 

Table 3: Analysis of Critical Incidents by Team 

 Local navigation Obstacle encounter Vehicle state 

Team A 4 6 5 

Team B 1 9 2 

Team C 10 11 5 

Total 15 26 12 

Obstacle encounters were the most prevalent types of critical incidents. Robots became entangled in loose 

debris in the arenas and it was difficult for the operators to know that. 

In the most recent competition, Robocup 2004, we noted that teams typically had one of two sources of 

situation awareness information implemented. A number of teams used some sort of overhead cameras to 

provide a frame of reference for the robot in relationship to the environment. Other teams had 

implemented some sort of automatic mapping software, using a variety of sensors, including sonar and 

ladar. At this point we have not had time to do a full analysis, but an early analysis looks at the five teams 

who were in the final runs. Table 4 shows the penalties by team. 

Table 4: Penalties by type of situation awareness 

Penalties for teams using automatic mapping Penalties for teams using overhead cameras 

Team A 0 Team P 80 

Team D 5 Team S2 5 

Team S1 40 (note Team S2 had only 3 runs completed as they 

had to end one run prematurely due to a problem 

with the robot) 
These penalties are all local navigation penalties. That is, the robot either bumped into the walls of the 

arena or into a victim. While these results should be viewed as very preliminary, our impression is that the 

automatic mapping is more helpful in providing situation awareness. This is not surprising, as the video 

information, while helpful, still requires considerable interpretation by the operator. Also, if there happens 

to be any sort of communication interference, the video is extremely difficult to view. The teams that we 

analyzed were the top scoring teams, which implies that they had reasonable coverage of the area and 

located a number of victims. Low scoring teams may have few penalties due primarily to an inability to 

move very far into the USAR arena. 

The majority of teams we have analyzed have been teleoperated, using autonomy only for such things as 

mapping. While we have had some fully autonomous teams in the competitions, they have not been 

successful in navigating the difficult environment in the test arena. In our first analysis, two of the teams 

operated in semi-autonomous modes. The operators were responsible for overall navigation, but left the 

local navigation (obstacle avoidance, waypoint navigation) to the robots in many instances. We intend to 

analyze future teams to determine how critical incidents change based on the level of autonomy. 

Discussion 

Based on the analyses we have completed to date, we have been able to provide some guidelines for 

human-robot interaction design. These are summarized below. 

• Information for effective situation awareness should include: 

o a frame of reference to determine the position of the robot relative to the surrounding 

environment 

o indicators of vehicle state, such as pitch, roll, traction indicators, indicators of sensor 

status, and camera positions relative to the robot body. 

o a map to provide global navigation information 

• Minimize the number of windows provided to the operator. 

• Provide a fused view of sensor information. 

• Support multiple robot operators in a single display. 

• Provide help from the robot in determining what mode of autonomy is most useful. 

To date, we have been able to analyze data collected during USAR competitions to provide some 

guidelines for the design of effective user interfaces for USAR robots. We are encouraged that our work is 

making a difference as the situation awareness offered in the user interfaces deployed in current 

competitions is certainly increasing. The downside of our work is that the analysis takes considerable time 

and by and large the results are consumed by human-computer interaction researchers, not robotics 

researchers. 

Future Plans 

We are interested in providing feedback about HRI designs in a more timely fashion and to the robotics 

community more directly. In the final rounds of Robocup 2004, robots were placed in an internal spot in 

one of the arenas. The operator had to first assess where the robot was and then devise a strategy for 

moving out into the arena to locate victims. We are currently working on devising extensions to this, 

similar to the compulsories in figure skating competitions. This would help us assess during the 

competition how well the operator is able to gain situation awareness based on the user interface. While 

the NIST Reference Arenas provide a standard area in which the robots have to perform, there is no 

guarantee that robots encounter the same obstacles. Moreover, due to variations in size and mobility, we 

cannot expect robots to do equally well in navigating the same environment. 

It is important for effective search and rescue that teams are in control. This means having good SA at all 

time about where team members, including robots, are and what they are doing. Situation awareness could 

be demonstrated by placing robots in specific situations (such as close to obstacles, on different types of 

surfaces and grades, or near negative obstacles) and measuring the time and accuracy of the SA by the 
operator –robot team. We are working on a user interface design for our own robotics platform. It would 

be possible to consider our performance as a baseline that the teams should try to best. 

References 

1. Burke, J., R. Murphy, and M. Coovert. (2004). Moonlight in Miami: An Ethnographic Study of 

Human-Robot Interaction in the Context of an Urban Search and Rescue Disaster Response 

Training Exercise. Human Computer Interaction. 

2. Casper, J. (2002). Human-Robot Interactions During the Robot-Assisted Urban Search and 

Rescue Response at the World Trade Center. MS Thesis, University of South Florida Department 

of Computer Science and Engineering. 

3. Drury, J. L., J. Scholtz, and H. A. Yanco. Awareness in human-robot interactions. Proceedings of 

the IEEE Conference on Systems, Man and Cybernetics, Washington, DC, October 2003. 

4. Endsley, M. 2000. Theoretical Underpinning of Situation Awareness: Critical Review (2000) in 

Mica R. Endsley and Daniel J. Garland (Eds.) Situation Awareness Analysis and Measurement. 

Lawrence Erlbaum Associates, Mahwah, New Jersey. 3-32. 

5. Ericsson, K. A. and H. A. Simon (1980). “Verbal reports as data.” Psychological Review, Vol. 87, 

215 - 251. 

6. Ericsson, K. A., & Simon, H. A. (1993). Protocol Analysis: Verbal Reports as Data. Cambridge, 

MA: The MIT Press. 

7. Jacoff, A., E. Messina, and J. Evans (2001). “A reference test course for autonomous mobile 

robots.” In Proceedings of the SPIE-AeroSense Conference, Orlando, FL, April. 

8. Jacoff, A., E. Messina, and J. Evans (2000). “A standard test course for urban search and rescue 

robots.” In Proceedings of the Performance Metrics for Intelligent Systems Workshop, August. 

9. Scholtz, J., J. Young, J. Drury, and H. Yanco. (2004). “Evaluation of Human-Robot Interaction 

Awareness in Search and Rescue.” ICRA 2004. 

10. Scholtz, J., B. Antonishek, and J. Young. (2004). Evaluating human-robot interfaces: 

development of a situational awareness assessment methodology. Hawaii International 

Conference on System Science 37 (HICSS 37). Hawaii, Jan. 2004. 

11. Scholtz, J. (2003). Theory and Evaluation of Human Robot Interactions, Hawaii International 

Conference on System Science 36 (HICSS 36). Hawaii, Jan., 2003. 

12. Scholtz, J., B. Antonishek, and J. Young. (2003). Evaluation of Operator Interventions in 

Autonomous Off-Road Driving. In Proceedings of the Workshop on Performance Metrics for 

Intelligent Systems, (PERMIS). Gaithersburg, MD Sept. 2003. 

13. Scholtz, J., B. Antonishek, and J. Young (2004). Operator Interventions in Autonomous Off-road 

Driving: Effects of Terrain. To appear in Proceedings of the IEEE Conference on Systems, Man 

and Cybernetics, The Hague, NL October 2004. 

14. Yanco, H., J.L. Drury, and J. Scholtz. (2004). Beyond Usability Evaluation: Analysis of HumanRobot Interaction at a Major Robotics Competition.. Human-Computer Interaction, 2004. 
Task Performance Metrics in Human-Robot Interaction: Taking a Systems 

Approach 

Jennifer L. Burke, Robin R. Murphy, Dawn R. Riddle & Thomas Fincannon 

Center for Robot-Assisted Search and Rescue 

University of South Florida 

Tampa, FL 33620 

ABSTRACT

Performance metrics for human-robot interaction in urban search 

and rescue (USAR) are just beginning to appear in the literature as 

researchers try to establish a way of describing and evaluating 

human-robot task performance in this high-risk, time-critical 

domain. In this paper we propose that human-robot interaction 

metrics should focus on the work system as a whole, examining 

the robot’s effects on human task performance within the 

overarching context of human work. Moreover, these effects 

should be examined within the context of real-time human 

performance in field settings, rather than in simulation or 

experimental environments. This position stems from a basic 

assumption that we are interested in measuring human-robot 

interaction in USAR because we want to see how it affects and 

aids human performance in this time and safety-critical 

environment. We present a methodology for collecting data in the 

field and subsequent analysis using the Robot-Assisted Search and 

Rescue Coding System (RASAR-CS), specifically developed for 

this domain. The RASAR-CS allows us to capture 1)basic verbal 

and non verbal communications describing the task and how it is 

accomplished (what is being said, by who to whom); 2)situation 

awareness information requirements (from the robot and other 

sources) - for developing and maintaining situation awareness, 

including the ability to capture changing requirements over time; 

3)team processes enabling coordinated activities, efficient 

communication and strategy planning; and 4) human-robot 

interaction in terms of: robot-operator initiated robot activities, and 

physical interaction with robot. 

KEYWORDS: human-robot interaction, performance 

metrics, field methodologies

1. INTRODUCTION 

Human-robot interaction in the Urban Search and Rescue 

(USAR) domain is a field of study that has drawn 

increasing interest in light of the use of robots at the World 

Trade Center [5] and its designation as a benchmark domain 

in the seminal DARPA-NSF study on Human-Robot 

Interaction conducted in 2001 [2]. Performance metrics for 

human-robot interaction in USAR are just beginning to 

appear in the literature as researchers try to establish a way 

of describing and evaluating human-robot task performance 

in this high-risk, time-critical domain. In the aforementioned DARPA-NSF study, simple base measures were 

proposed: the ratio of persons to robots (h-r ratio), spatial 

relationships (commander, peer, teleoperator, developer) 

and authority relationships (supervisor, operator, peer and 

bystander). Some of the metrics proposed subsequently 

focus on aspects of the robot system exclusively, (e.g., the 

interface) or on aspects of human performance solely in 

relation to working with the robot [8, 9, 14]. In this paper 

we take a more human-centric position: human-robot 

interaction metrics should focus on the work system as a 

whole, examining the robot’s effects on human task 

performance within the overarching context of human work. 

This position stems from a basic assumption that we are 

interested in measuring human-robot interaction in USAR 

because we want to see how it affects and aids human 

performance (ultimately, that is the goal for measuring 

human-robot interaction in any work-related field or 

application). 

1.1 Field Studies in USAR 

Field studies conducted with rescue workers offer the most 

valid setting in which to study human-robot interaction. 

USAR is an established work environment offering 

opportunities to study the effects of introducing robotic 

technology into a workplace and occupation with existing 

goals, tasks and processes. It is arguably one of the first 

workplace applications where robots work in the same 

spaces with people whose jobs do not normally involve 

robotics to perform a task (Industrial robots are usually 

separated from humans, and are not mobile). Moreover, 

robots have been used in real disaster responses, and are 

gradually becoming incorporated into USAR training both 

nationally and internationally. Real-time high fidelity 

training exercises are conducted regularly in order for 

USAR task force members to attain or maintain certification; 

these exercises offer a double advantage for studying HRI in 

that the targeted end-users may be observed performing in 

realistic work environments. USAR task forces can be 

characterized as extreme teams [11] who function in 

dynamic, high risk, time critical environments. Team 

members must function in conditions which are often 

physically, mentally and emotionally taxing. Field studies 

with participants who are truly representative of this user 

group for whom the technology is being optimized offer the 

most power in terms of generalizability. 
1.2 Focusing on Human Performance 

Measures of human-robot interaction in USAR must focus 

on human performance. The current state of the practice in 

robot-assisted search and rescue is teleoperation. Though 

autonomous and semi-autonomous robots may soon be 

entering the workplace, they will still be machines designed 

to perform tasks as determined by a person. Robots are not 

conscious, they have no projects of their own other than 

those assigned to them. Clancey [7] points this out to 

illustrate that it’s too soon to talk about human-robot 

cooperation or collaboration: instead, robots serve as 

assistants to people working toward a project goal. 

Therefore the measure of a robot’s usefulness, efficiency 

and functionality is based solely on whether it contributes to 

helping a person (or team) accomplish a goal by making 

that person’s or team’s task performance more efficient, 

effective, or easy in some way. This means measuring 

human performance (aided by robots) is the key. This is 

different from the position taken in Drury et al. [9] that 

usability requirements, which focus primarily on the robotic 

system, are the most appropriate way to measure humanrobot interaction. We believe human-robot systems must be 

examined and measured in terms of their effect on human 

performance, since that is what they are designed to 

augment or improve. 

What are the criteria for measures of robot-assisted 

human performance in USAR? In this domain there are 

established goals: search, rescue (extrication), structural 

evaluation, medical assessment & treatment, information 

transfer, command & control, and logistics. Blitch [1] 

pointed out the potential applications of robots in tunnel and 

confined space search: now, it is evident that there are many 

more tasks in which robots may play a part in USAR, e.g. 

medical reachback, shoring, communications & information 

transfer, and safety monitoring. Past experience shows that 

new technologies evolve when they reach the workplace, 

and many times end up performing tasks or serving 

purposes for which they were not originally intended. What 

we can do is identify tasks as they emerge, study the 

human-robot interaction processes and determine optimal 

task allocation and roles, understanding that this is an 

iterative process that will change as the technology 

advances. Based on these tasks, we can measure humanrobot performance both individually (one person operating a 

robot) and in teams (more than one person operating a robot 

or robots). 

Our field research has shown that situation awareness 

and team processes are two constructs which relate to 

human performance when working with robots [3, 5, 6]. 

Situation awareness (SA) as defined by Endsley [10] is 

“...the perception of the elements in the environment within 

a volume of time and space, the comprehension of their 

meaning and the projection of their status in the near future” 

(p. 97). Our studies have shown situation awareness to be 

related to performance and that most of the operators’ time 

is spent gathering/maintaining situation awareness [3, 4]. 

Operators with high situation awareness ratings were better 

performers in our study of 28 robot operators [4]. Team 

processes are also related to operator performance; 

operators who talked more with their teammates about goaldirected aspects of the task had higher situation awareness 

ratings and found the victim more often. There is an 

interactive affect between situation awareness and team 

process—suggesting operators who talk more with their 

tether manager or teammate are better at building a mental 

model of the robot as it functions in the void space, and also 

are better at building a shared mental model of the search. 

Research on teams and mental models has suggested that 

having a shared mental model of the problem space can 

increase situation awareness and team performance [11, 16]. 

Effective planning and communication strategies were 

found to increase team shared mental models and 

correspondingly team performance. Therefore, human-robot 

interaction in USAR needs to be measured not only at the 

individual level, but also at the team level. 

2. METHODOLOGY 

In this section we present our methods of field data 

collection and data analysis, including a description of the 

Robot-Assisted Search and Rescue Coding System 

(RASAR-CS). 

2.1 Data Collection in the Field 

Data collection is an observational procedure, where the 

researcher is present during the user-robot interaction, 

though not an active participant. We tape the interaction 

using 2-4 cameras depending on the environment (Table 1). 

Minimally, one camera records the robot’s eye view directly 

from the operator control unit (OCU), and a second camera 

records the operator (making sure to have a clear view of 

the face) as she works with the robot. When environmental 

conditions permit, we set up a third camera on a tripod to 

record the operator’s hands manipulating the OCU, and a 

fourth camera to record an external view of the robot when 

available. Depending on the environment and the number of 

personnel available for the data collection process, some 

cameras may be fixed on tripods; however, in USAR 

conditions, most of the time views 2-4 must be handheld 

due to lack of level spots for setting up a fixed camera. 

Video recordings of the operators manipulating the robot, 

the robot’s eye view, and the available external views are 

edited and synchronized to create tapes with 2 views sideby-side. These videotapes are then used to code statements 

and gestures made by both the operators and surrounding 

personnel, and robot movements. Trained raters code the 

videotapes using the Noldus Observer Video-Pro [13] 

observational coding software. 
Table 1. Camera views for human-robot interaction

field research in USAR. 

2.2 Video-based Interaction Analysis 

What, then, are some appropriate measures and metrics for 

USAR human-robot interaction? Primary human

performance outcome measures for search at the most basic

level include: Was a victim found, how long did it take, 

were any victims missed, were important cues noticed (heat, 

color, objects, information synthesis with knowledge about 

the event & environment)? Other measures that are related 

to these primary outcomes specifically measure situation

awareness and team processes. These measures are gathered

via a video-based Interaction Analysis technique for 

investigating HRI in rescue robotics. Interaction Analysis 

(IA) is an interdisciplinary approach to studying the 

interaction of humans with each other and with objects in

their environment. Jordan & Henderson [12] assert, 

“Video-based Interaction Analysis is a powerful tool in the 

investigation of human activity that is particularly effective 

in complex, multi-actor, technology-mediated work

settings ... It is currently undergoing a period of rapid

development, driven, in part, by researchers' dissatisfaction

with conventional methods, and in part by the ubiquity of

video equipment.” (p.44) 

The goal of Interaction Analysis is to identify 

regularities in the ways in which participants utilize the 

resources of the complex social and material world of actors 

and objects within which they operate. To do this we must 

examine two components of IA, which are intertwined, but

distinct as well: human-human interaction, and humanobject interaction. Interaction Analysis assumes that 

knowledge and action are fundamentally social in origin, 

organization, and use. Knowledge is seen as located in the 

interactions between people engaged with the material 

objects in their surroundings; therefore communication 

analysis plays an important role in Interaction Analysis as a 

means of analyzing human-human interactions. 

Although variety of approaches to examining 

communication, we chose the FAA’s Controller-toController Communication and Coordination Taxonomy

(C4

T) [15] framework as the starting point for the 

development of our communication analysis system

designed to assess HRI in rescue robotics. The C4

T uses

verbal information to assess team member interaction from

communication exchanges in an air traffic control 

environment. We used the C4

T model because it captures 

the “how” and “what” of team communication by coding 

form, content and mode of communication. Our goal, 

however, is two-fold, not only to capture the “how” and

“what” of USAR robot operator teams, but also the “who”, 

and to capture observable indicators of robot operator 

situation awareness. In addition, in order to adhere to the 

tenets of IA, the framework must be extended to include 

examination of physical interactions with the robot system(s) 

in the environment. 

Camera 

No.

View Setup

1 Robot’s eye view Attached to OCU 

2 Operator view Tripod or handheld 

3 Operator-OCU view Tripod or handheld 

4 Robot-external view Tripod or handheld 

2.3 Robot-Assisted Search and Rescue Coding 

System (RASAR-CS)

A methodology to capture and assess robot assisted task 

performance in rescue robotics must consider both human 

team member interactions (robot operator and other team

members), and human – robot interactions. To meet the 

goals of a methodology capable of defining robot assisted

tasks, and examining SA and teamwork defined earlier, we 

developed the Robot-Assisted Search and Rescue Coding

System (RASAR-CS). The RASAR-CS captures Basic

verbal and non verbal communications describing the task

and how it is accomplished (what is being said, by who to 

whom); Situation Awareness Information requirements

(from the robot and other sources) - for developing and 

maintaining situation awareness, including the ability to

capture changing requirements over time; Team processes

enabling coordinated activities, efficient communication

and strategy planning; and Human-Robot interaction in

terms of: Robot-operator initiated robot activities, and

Physical interaction with robot. 

Following the Interaction Analysis approach, the 

RASAR-CS consists of four main coding components 

enabling analysis of SA and team factors through humanhuman interaction and human robot interaction. These 

components include verbal communication, communication 

medium, nonverbal interaction and robot movements. 

2.3.1 Human-Human Verbal Communication 

The verbal communication analysis codes team member 

statements across four categories: 1) Speaker-recipient dyad

- who is speaking to whom, 2) Content or topic of the 

communication 3) Statement form or grammatical structure

of the communication, 4) Function or intent of the 

communication (Table 2). By examining dyad, content, and

form, we can examine task procedures and team

coordination. Similarly, content and function provide

indicators of operator situation awareness.

Speaker-recipient dyad. Based on review of the search

task videotapes, potential conversants included the operator, 

tether manager, team member, the group, and the robot 

specialist/researcher. Dyad codes indicate the speaker, 

followed by the recipient. For example, “operator-tether 

manager” indicates a statement was made by the operator
Table 2. RASAR-CS (for USAR search task)

Category Subcategories Definitions

Human-Human Verbal Communication

Operator-tether manager Operator: individual teleoperating the robot 

Tether manager-operator Tether manager: individual manipulating the tether and assisting operator with robot 

Team member-operator Team member: one other than the tether manager who is assisting the operator (usually interpreting) 

Operator- team member 

Researcher-operator Researcher: individual acting as scientist or robot specialist 

Operator-researcher

Other-operator Other: individual (not tether manager, team member, or researcher) interacting with the operator 

Operator-other

Sender/Recipient 

Dyad 

Operator-group Group -set of individuals interacting with the operator

Robot state Robot functions, parts, errors, capabilities, etc.

Environment Characteristics, conditions or events in the search environment 

Information synthesis Connections between current observation and prior observations or knowledge 

Robot situatedness Robot’s location and spatial orientation in the environment; position 

Victim Pertaining to a victim or possible victim

Navigation Direction of movement or route 

Search strategy Search task plans, procedures or decisions 

Content 

Off task Unrelated or extraneous subject 

Question Request for information 

Instruction Direction for task performance 

Comment General statement, initiated or responsive, that is not a question, instruction or answer Statement Form

Answer Response to a question or an instruction 

Non-operator Default for statements made by individuals other than the operator

Seek information Asking for information from someone 

Report Sharing observations about the robot, environment, or victim

Clarify Making a previous statement or observation more precise

Confirm Affirming a previous statement or observation 

Convey uncertainty Expressing doubt, disorientation, or loss of confidence in a state or observation 

Plan Projecting future goals or steps to goals 

Function 

Provide information Sharing information (other than report) in response to a question or offering unsolicited information 

Team Coordination Team members coordinate actions to synchronize specific proximal task activities 

Communication Planning Planned strategies for future goal accomplishment

Audio Verbal information or information from previous dialog 

Visual image Robot image or information from image provides the basis for statement 

Source of 

Information used

in discussion Sensor Sensor or information from sensor provides the basis for statement

Human-Robot Interaction (Nonverbal interaction via the robot) 

Ear to robot Ear is directed toward the robot 

Eye to robot Turning so that the human looks at the robot 

Physical

orientation 

No verbal communication No verbal communication with the operator 

Come forward Motioning toward the robot to move forward 

Thumbs up Closing the fist with the thumb extended upward 

Stop Holding up a hand with the palm toward the r

Pointing Using fingers to point in a particular direction or at a specific object 

“OK” sign Closing the thumb and forefinger in a circle indicating the “OK” sign 

Gestures

Other Other gestures (usually conversational with no intended message)

Clean lens Cleaning the robot camera lens 

Move/shift Altering the position of the robot 

Pick up Lifting the robot off the surface upon which it is moving 

Interaction with

Robot 

Other Other physical contact with the robot 

Moving Forward or backward locomotion 

Robot Movement Stationary No movement at all 

Panning Rotating side to side without forward movement, or manipulating the camera lens up/down 
and directed toward the tether manager (Note: the code 

“tether manager – operator” indicates the tether manager 

initiated the communication with the operator). 

Content. Seven elements representing the content were 

generated: 1- Statements related to robot functions, parts, 

errors, or capabilities (Robot state), 2- Statements 

describing characteristics, conditions or events in the search 

environment (Environment), 3- Statements reflecting 

associations between current observations and prior 

observations or knowledge (Information synthesis), 4- 

Statements surrounding the robot’s location, spatial 

orientation in the environment, or position (Robot 

situatedness), 5- Indicators of direction of movement or 

route, (Navigation), 6- Statements reflecting search task 

plans, procedures or decisions (Search Strategy), and finally 

7- Statements unrelated to the task (Off Task). The first 

four content elements are relevant to building and 

maintaining SA in search operations, while the elements of 

navigation and search strategy require SA. 

Form. Similar to the C4

T taxonomy, the form category 

contains the elements: 1- Question (request for information), 

2- Instruction (direction for task performance), 3- Comment 

(general statement, initiated or responsive, that is not a 

question, instruction or answer) and 4- Answer (response to 

a question or an instruction). 

Function. Function refers to the intent of the 

communication - elements include: 1- Seek information 

(asking for information from someone), 2- Report (sharing 

observations about the robot or environment), 3- Clarify 

(making a previous statement or observation more precise), 

4- Confirm (affirming a previous statement or observation) 

5- Convey uncertainty (expressing doubt, disorientation, or 

loss of confidence in a state or observation), 6- Plan 

(projecting future goals or steps to goals), 7- Provide 

information (sharing information other than that described 

in report, either in response to a question, or offering 

unsolicited information). 

The function elements of reporting and providing 

information merit explanation, as they appear very similar. 

Reporting involves perception and comprehension of the 

robot’s state or situatedness, the environment or information 

synthesis. Any other information shared by an operator, in 

answer to a question or on his own, is classified as 

providing information (for example search strategy or 

navigation). Indicators of SA are captured in the function 

category primarily through the elements reporting and 

planning. When operator shares information (reports) based 

on the robot’s eye view, we can infer the first two levels of 

SA, perception and comprehension, have taken place. The 

third SA level, planning and projection, is captured in the 

function category as the element “plan.” 

2.3.2 Team 

Communication. Team communication offers insights into 

how goals are accomplished. Categories include: 

1- Coordinating activities (to synchronize specific proximal 

task activities) and 2- Planning (for future goal 

accomplishment). 

Medium. Team communication is also coded according 

the medium used to in conveying information: 1- Visual 

(visual image provided the foundation for the 

communication), 2- Auditory (verbal information provided 

the foundation for the communication), and 3- Sensor 

(sensor provided the foundation for the communication). 

2.3.3 Human – Robot Interaction 

Nonverbal interaction with robot. Nonverbal HRI includes 

nonverbal communication between humans via the robot 

camera, and physical interaction of humans with the robot. 

When robots are co-located with humans, humans 

physically orient to the robot and use gestures when 

communicating with the operator in control of the robot. 

Additionally, humans have the ability to physically touch or 

interact with the robot to cooperatively accomplish goals. 

The three main nonverbal categories include: physical 

orientation, gestures, and physical interaction with colocated robot. 

Physical orientation. Physical orientation includes 

positioning the body during communication with the robot 

operator so that the 1- Ear is directed toward the robot (ear 

to robot), and 2- Turning so that the human looks at the 

robot (eye to robot). 

Gestures. Again, while communicating with the robot 

operator, gesture can be used to convey meaning to the 

operator via the robot camera. Gestures include: 1- Come 

forward (motioning toward the robot to move forward), 2- 

Pointing (using fingers to point in a particular direction or at 

a specific object), 3- Thumbs up (closing the fist with the 

thumb extended upward), 4- Stop (holding up a hand with 

the palm toward the robot), and 5- OK (closing the thumb 

and forefinger in a circle indicating the “OK” sign). 

Physical Interaction with Robot. Physical interaction 

codes include: 1- Clean lens (cleaning the robot camera 

lens), 2- Move/shift (altering the position of the robot), and 

3- Pick up (lifting the robot off the surface upon which it is 

moving). 

Robot Movement. The three major robot movement 

coding categories of the RASAR-CS include: 1- Moving 

(traveling forward or back), 2- Stationary (no movement at 

all) and 3- Panning (turning from side to side without 

forward or backward movement). 

3. CONCLUSIONS 

We have presented a field methodology for examining 

human-robot interaction in USAR which focuses on robotassisted human performance. Using a video-based 

Interaction Analysis technique, we examine both human-
human interaction and human-robot interaction with 

measures designed to capture performance of human-robot 

systems. The Robot-Assisted Search and Rescue Coding 

Scheme enables us to 

• Examine archival videotaped data. Video data 

involving users provides a richness of information 

that we previously had no established means of 

harvesting. 

• Decompose novel robot assisted tasks.

Understanding how USAR personnel use robots to 

accomplish tasks provides the foundation for 

developing a model of robot assisted task 

performance, which can be used for defining best 

practices and generating field training. 

• Identify task specific SA requirements and effective 

modalities for information transfer among team 

members for use in system design (e.g., operator 

control unit interfaces, and web pages for remote 

team members). 

• Evaluate requirements for team performance such 

as shared mental models, coordination of activities, 

and patterns of cooperative behavior.

• Obtain quantifiable SA and team data for 

evaluating effective performance. 

• Adapt and respond to changing task and 

technology requirements. The RASAR-CS can be 

reconfigured to meet needs of various tasks and to 

be responsive to changes in technology as 

advances in robotics occur. 

The RASAR-CS allows researchers to decompose 

both human-robot and human-human interaction in a 

meaningful way to define robot assisted task performance 

including task procedures, situation awareness requirements, 

and team process and coordination. The system can be 

applied across tasks and domains by utilizing the procedures 

outlined for modifying the relevant codes. In assessing 

complex environments it is important to use multiple 

methods of assessment. The RASAR-CS is an effective 

methodology to add to researchers’ HRI toolkit for analysis 

of archival videotapes of field data, or used as a 

complement to other techniques, e.g. onsite expert ratings of 

situation awareness and team process, self ratings of 

situation awareness and team process, and user ratings of 

traditional evaluative components (usefulness, ease of use, 

effectiveness, satisfaction) for using the robot. 

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Reduction of User Interaction by Autonomy 

Arin Morfopoulos, Michael McHenry, and Larry Matthies 

Jet Propulsion Laboratory 

4800 Oak Grove Drive, Pasadena, CA 91109 

{arin.morfopoulos, michael.mchenry, larry.matthies}@jpl.nasa.gov

Abstract

This paper describes experiments that quantify the improvement 

that autonomous behaviors enable in the amount of user interaction 

required to navigate a robot in urban environments. Many papers 

have discussed various ways to measure the absolute level of 

autonomy of a system; we measured the relative improvement of 

autonomous behaviors over teleoperation across multiple traverses 

of the same course. We performed four runs each on an “easy” 

course and a “hard” course, where half the runs were teleoperated 

and half used more autonomous behaviors. Statistics show 40-70% 

reductions in the amount of time the user interacts with the control 

station; however, with the behaviors tested, user attention remained on the control station even when he was not interacting. 

Reducing the need for attention will require better obstacle detection and avoidance and better absolute position estimation. 

Keywords: User interaction, attention, autonomy, robot. 

1. Introduction 

The usefulness of mobile robots is a strong inverse function of the amount of user interaction required to control 

them; hence, the value of autonomous behaviors is partly a 

function of how much they reduce the amount of user interaction required. Thus, quantifying user interaction as a function of the available robot control modes is necessary for 

measuring progress. Quantitative user interaction experiments can also reveal where existing robot behaviors have 

trouble dealing with the environment, and therefore are useful for prioritizing further development. 

 In this paper, we describe results of user interaction experiments with a Packbot robot equipped with stereo cameras, a single axis scanning LADAR, and a variety of behaviors ranging from teleoperation to waypoint following 

with obstacle avoidance. We counted user button clicks and 

mouse drags in a series of trials employing different behaviors over two courses, an “easy” course and a “hard” course. 

Two trials on each course used just teleoperation, two used 

more autonomous behaviors. We did not measure the 

amount of time the user was watching the control station (ie. 

user attention) when he was not physically interacting with 

it. This is an important additional step needed in future 

work. As we will show, however, current autonomous capabilities still require considerable user attention even though 

user interaction per se may be small, because robots are 

likely to get in trouble if the user is not watching an image 

stream from the robot. 

 The rest of this paper is organized as follows. First, section 2 reviews related prior work. Then we describe our 

experimental setup and how we collected the data (Section 

3). The actual data collection follows this with all the attendant graphs and tables (Section 4). We use these results to 

highlight key areas where more development is needed to 

reduce both user interaction and user attention. The most 

significant areas are position estimation and path planning 

capabilities that enable autonomous traverses beyond line of 

sight from the robot (Section 5) and obstacle detection and 

avoidance capabilities that can cope with negative obstacles 

and moving objects, such as cars and people (Section 6). 

2. Related Work 

Goodrich, Crandall et al [1,6,7,8] have done a series of 

user interaction and attention studies. Their data lies chiefly 

in robotic simulation, which allowed them to force the 

user’s attention to another task and to quantify the effect of 

user inattention upon performance. They call this “neglect 

tolerance”. We could not afford to quantify this, because 

real robots currently face too much risk of damage from 

unseen obstacles and moving traffic when the user is not 

attending to downlinked imagery. Goodrich, Crandall et al 

have also defined a general model of teleoperation, waypoints, and scripted waypoints in terms of interaction vs. 

performance. This is a theoretical model that closely describes the behaviors we use. Teleoperation requires constant interaction whereas waypoints require more work to 

initiate, but once started can be left alone for a much longer 

period. 

Tejada [3] discussed a model for a 3-D graphical user interface to use with urban search and rescue teams. Our experiment did not quantify the effect of different Operator 

Control Units, since our focus was on the effect of different 

behaviors in the robot. 

Frost [4] discussed the difficulties of pure teleoperation, 

but only as general observations. No measured times to 

complete a course or accomplish an objective are given. 

This paper is particularly relevant because it describes the 

same robotic platform with which we conducted our tests. 

The autonomy used was entirely different, but the chassis 

and thus mechanical ability was the same. 
Bruemmer [5] used a robotic system to work in a nuclear 

disposal facility. Their work described the difficulties of a 

teleoperated system using only visual feedback for control 

information. They were forced to place cameras inside each 

room to have enough data to allow safe navigation because 

the view from the robot’s cameras was not sufficient. As a 

result of these difficulties they devised an autonomous system to assist in control and to prevent the user from endangering the robot or the environment. This is an excellent 

example of where it would be valuable to quantify the benefit of new behaviors. They tried teleoperation, found it lacking, created autonomy to assist, but have not yet measured 

the improvement enabled by that autonomy. 

3. Experiment Setup 

The robotic platform in our experiments (“Urbie”) was an 

iRobot Packbot chassis with an electronic payload developed by JPL under the Tactical Mobile Robotics (TMR) and 

Mobile Autonomous Robot Software (MARS) programs 

sponsored by DARPA. Urbie’s sensors included a black and 

white stereo camera pair, a SICK LADAR, 3-axis accels 

and gyros, a magnetometer with pan/roll/tilt axes, and track 

encoder feedback. Robot state was maintained by a Kalman 

filter which estimated the orientation (roll/pitch/yaw) of the 

robot. The KF orientation estimate was combined with the 

track encoder data to produce an estimate of robot x/y position via dead reckoning. 

Behaviors used included visually designated waypoint 

following, stairclimbing, and teleoperation. An Obstacle 

Detection and Avoidance (ODOA) module could be dynamically incorporated via an arbiter system to make any of 

the above behaviors become Safeguarded. To use “visually 

designated waypoint following” a user selected a heading 

from the robot’s field of view and defined a desired distance; the robot would then attempt to hew to that line as 

closely as possible (while avoiding obstacles should ODOA 

be enabled). Stairclimbing allowed autonomous traverses of 

single flights of stairs. 

A single experienced user controlled the robot over each 

run. The user had feedback from one of the stereo cameras 

allowing a keyhole view of the environment from the robot’s perspective. Location of the robot’s current position 

relative to the starting position was recorded but not viewed 

during the run. 

Two courses were used: one fairly easy run taking place 

entirely on road surfaces and one comparatively hard run 

which involved driving on grass, sidewalks, and stairs as 

well as roads. Data was collected for four runs over each of 

the two courses. For each course two of the four runs used 

only teleoperation and the remaining two used autonomous 

behaviors. The hard course consisted of positive and negative obstacles, two flights of stairs and narrow pathways 

between positive and negative obstacles. The easy course 

was twice the distance but involved only paved roads with 

few obstacles. The user was familiar with each course and 

had walked them beforehand. Each course was designed as 

a navigational course rather than an exploration effort, in 

the sense that the user knew where he wanted to go and 

roughly what obstacles he would face. 

During each run all mouse clicks and drags were recorded and time stamped along with position. This allowed 

us to relate user interaction with the robot’s location. 

4. Data and results 

For each course we will show an overhead photo as well 

as graphs of a teleoperation run and an autonomous run. 

The graphs relate user interaction to the location at which 

that interaction occurred. The path of the robot is drawn in 

blue, and any user interactions are denoted by an ‘X’ superimposed on the path where the interaction took place. The 

robot’s location was recorded for every 20 cm traveled, and 

the size of the ‘X’ reflects the number of seconds the operator spent interacting with the control unit during that 20 cm 

segment. Specifically, marker size is proportional to the 

cube root of the interaction seconds per segment. Thus a 

point drawn 3 times the size of another point represents 9 

times as much interaction. 

The space between X’s indicates no user interaction. 

This indicates distance traveled using waypoints or stairclimbing, where the robot was entirely autonomous. 

After discussing each course we will show combined statistics gathered over all 8 runs.

4.1 Easy Course 

Fig. 1 is an overhead image of the Easy Course with the 

robot path drawn in red. Note that the entire path is along 

paved roads. 

 Fig 1. Overhead image of the Easy Course 
Stairs

Planter

Tree

Narrow Pathway Curb

Fig 2.Teleoperation over easy course Fig 3. Waypoint over easy course 

Fig 4. Overhead image of the Hard Course 

Fig. 2 and Fig. 3 show the graphs of user interaction as a function of position. Streets are overlain as 

hand-drawn lines. 

During the teleoperation run the user was interacting for the entire run, constantly commanding a direction. During the waypoint run the user could interact 

for brief intervals to set up a new waypoint and then 

wait. 

 Each waypoint was set to 30 meters and could only 

be selected with the current image from the robot. 

This forced the user to intervene in the curved portion 

of the first half of the path to change directions, 

whereas in the second half the user could wait for the 

30 meters to be reached before needing to interact 

again. 

4.2 Hard Course

 Fig. 4 displays the overhead image of the Hard 

Course with the chief obstacles labeled. Unlike the 

Easy Course, the path is over grass, sidewalks, streets, 

and up two flights of stairs. Negative obstacles forced 

the user to pay close attention during teleoperation 

and waypoints. Cars on the street required special 

concern and attention. Several situations were too 

complex for the autonomy on board and the user had 

to manually switch to teleoperation and guide the robot over the difficult sections.
Obstacles along the path (in the order they appear) are a 

• Tree

• Negative obstacle (planter on the right shown as a 

small square).

• Negative obstacle requiring traversal (curb).

• Moving obstacles (cars)

• Narrow pathway with a pole in the middle 

• Stairs 

 Fig 5. shows a sample run with only teleoperation. Notice that the points of interaction become denser in the 

difficult areas near the curb, stairs and narrow pathways. 

Hand drawn on the image are two obstacles (the tree and 

planter) as well as the street edges. 

 Fig 6. illustrates the mix of autonomous behaviors and 

teleoperation used for the Hard Course. 

A few areas should be emphasized: 

• The tree was avoided autonomously using ODOA. 

• The planter was avoided by manually aborting a waypoint and selecting a new waypoint. The ODOA capability on Urbie would not have avoided this negative 

obstacle. 

Fig 5. Teleoperation over Hard Course. Fig 6. Autonomous and Teleoperation behaviors 

• The robot could not go down the curb because the path 

was blocked by a car (not shown in the figure); we followed the curb, bounded by negative obstacles on either side. 

• Once past the car, the user was forced to teleop down 

the curb, as waypoint mode drives too fast to be safe. 

• The user could not do a line of sight waypoint directly 

to the base of the stairwell; instead he used 4 waypoints, one after the other. 

• The robot avoided the pole autonomously (shown as 

small circle in the middle of the narrow pathway). 

 Recall that there was no interaction on any path segment 

where no X’s appear. Any smooth, unblemished line was 

traveled autonomously. 

 In the Fig. 6 the stairwell took so much interaction over 

such a small distance that it appears no autonomy was used. 

In fact, waypoints were used to the base of the stairwell and 

autonomous stairclimbing was used up both flights of stairs. 

The landings required manual teleoperation to maneuver in 

such tight quarters. Fig 7. illustrates this with a closer view 

(the robot enters from the bottom of the graph, finishes the 

run to the right). 
Fig 7. Close-up of the stairwell. 

Easy Course Metrics

 

Hard Course Metrics

 

 Teleop Waypoint Teleop Waypoint 

Length (meters) 275 272 270 274 169 159 155 154 

Time of Run (seconds) 264 380 355 370 423 459 448 488 

Average Speed (m/sec) 1.24 0.72 0.76 0.74 0.40 0.35 0.35 0.32

Percent of time user interacting 99% 92% 30% 26% 81% 79% 51% 45%

User Interaction per meter (sec/m) 0.79 1.29 0.40 0.35 2.04 2.27 1.46 1.44

Percent of Distance Traveled 

Autonomously 0 0 99% 99% 0 0 80% 78%

Ave time of Autonomous Drive (sec) 0.00 0.00 14.65 18.93 0.00 0.00 9.55 13.11

Table 1. Interaction data over all 8 runs 

the path was generally straighter on the Easy Course. 

5. The time to complete a course did not improve as a 

result of autonomy, even though the speed during 

autonomy (not shown) was higher than during teleoperation. 

 A quick aside is necessary to explain Fig 7 properly. 

Only the first half of the first flight of stairs was traveled 

autonomously because a power fluctuation caused by the 

extreme driving conditions caused the communication link 

to be dropped. The user did not resume the stairclimbing 

behavior but simply teleoperated to the next flight. 

 A second oddity is that the second flight of stairs appears 

longer than the first, which is a result of extreme track slippage. Recall that the robot’s orientation estimate was combined with the track encoder data (which is unreliable on 

stairs) to produce an estimate of robot x/y position via dead 

reckoning. 

 At the top of the second flight of stairs the robot traveled 

through a doorway inside the building using teleoperation. 

4.3 Quantitative Measures 

 Table 1 the sum of all quantitative measurements over 

the 8 runs (with 4 runs per course). Attention should be 

directed to five areas in particular. 

1. Percent of time user interacting is not 100% during 

teleop runs because the user had to pause occasionally 

to observe the surroundings, during which time he is 

not actually issuing any commands to the robot. 

2. During the first teleop run on the Easy Course the user 

drove very aggressively and a little unsafely. The 

speed during this run is higher than the other 3 over the 

Easy Course. The user also never stopped to get his 

bearings during that run. 

3. The user was forced to use teleoperation over the Hard 

Course during a few difficult segments. The Percent of 

Distance Traveled Autonomously was below 100% 

during those runs as a result. 

4. The average time of autonomous segments on the Easy 

Course was longer than on the Hard Course because 
5. Autonomous Traverses Beyond Line of Sight

One interesting result is that autonomy did not reduce the 

overall time of the run even though the velocity during the 

autonomous waypoints was usually higher than a human 

driver would have been comfortable with in teleoperation. 

The setup time and piece by piece selection of waypoints 

took up the remaining time; each waypoint could only be 

selected from the robot’s current field of view, which only 

allows short traverses before being occluded by obstacles. 

The overall interaction time could have been much reduced if the user was able to select a series of waypoints at a 

time instead of waiting for the robot to finish each leg before commanding the next. Alternatively, the user could 

have selected a single goal, far in the distance, and trusted 

the robot get there autonomously. We call the first ability 

Scripted Waypoints and the second ability Single Point 

Goal Selection. 

5.1 Scripted Waypoints

The challenge with scripted waypoints is knowing the absolute position of the robot in a global reference frame. The 

problem is really twofold: a) how does the user know where 

he wants to go before the robot can see it and b) translating 

this point to a coordinate frame the robot can use to navigate 

to. 

The first part of the problem can be solved by providing 

the user with an overhead image or map of the terrain. In 

theory the user would be able to select points on the overhead image on the fly and have the robot drive from one to 

the next. 

The second part of the problem is translating the points 

that the user clicks on in an overhead image to a reference 

frame the robot can use to autonomously navigate to. The 

predominant global localization method is using GPS with a 

known relation between GPS coordinates and the overhead 

image. 

In general, obtaining GPS data in a dense urban setting 

can be difficult, at times impossible. The buildings to either 

side of the robot prevent the acquisition of enough satellites 

to provide meaningful data. In other types of terrain with 

significant sky coverage, GPS is a viable option and not to 

be discounted, but in many urban environments GPS availability can not be assumed. 

An attractive alternative is to use the buildings themselves as landmarks to help localize the robot. Recent work 

at JPL has shown that it is possible to use vision algorithms 

to extract features from onboard imagery, to match those 

features to known buildings derived from the overhead image, and thereby to estimate the position of the robot in the 

global reference frame. This option is under ongoing development in the MARS program and would be a great boon to 

autonomous capabilities for terrain types where GPS is unavailable. 

This option has the additional benefit of being viable 

within buildings, where GPS is nearly guaranteed to fail. 

The feature template could be a rough blueprint of the site 

or a sequence of pictures taken by hand during some reconnaissance run a priori. In either case the robot could continue to calculate its position in an absolute reference frame, 

allowing better state estimation and bounding absolute error. 

5.2 Single Point Goal Selection 

An autonomous behavior above and beyond scripted 

waypoints would be a single waypoint, very distant, with 

enough path planning ability on board to get there without 

further advice. The two greatest challenges to do this are a 

sophisticated path planner and a very accurate state estimator. 

The path planner would have to be capable of escaping 

cul-de-sacs, navigating narrow path ways and capable of 

broad goal definitions. 

Even with a perfect path planner, accurate position in the 

global reference frame is still needed. GPS could provide 

this global frame, but as we discussed it may not be available. Without a global position sensor, any state estimator, 

such as the Kalman Filter we used on our robot, will drift 

over time. Although usually very accurate, our filter did not 

tolerate climbing stairs or driving off of curbs very well. 

The sudden acceleration and deceleration, as well as extreme track slippage and skidding, brought about a slight 

error in pose every time. Compounded over another 50 meters of travel this slight error would grow to several meters 

of error in the pose estimate. As discussed in 5.1, matching 

vision sensor data to a prior map obtained from overhead 

imagery is a promising approach to this problem. 

6. User Attention 

The user looked at the robot feedback during the entire 

course of each run. He never looked directly at the robot, 

but neither could he look away from the screen to do anything else. In any real application, this is a critical flaw. The 

main reason that constant attention was needed was that the 

robot’s current ODOA capability was not adequate to keep 

it out of trouble that could damage the robot or terminate the 

mission. The main types of trouble that could be encountered were negative obstacles and moving objects. 

6.1 Negative Obstacles 

Urban settings are rife with negative obstacles: planters, 

stairs, curbs, and walkway edges. Rails that prevent humans 

from walking off pathways are often placed too high to be 

spotted by ODOA and allow the robot to travel without resistance into a crevasse. Some negative obstacles such as 

curbs are traversable, but only at low speeds. Although 

negative obstacle detection has been addressed for years for 

cross-country navigation, even there the problem is not 

completely solved, and we have not yet integrated such capabilities into Urbie. Moreover, the urban domain has 
unique characteristics that could profit from algorithms designed specifically for it. 

The inability of our autonomous system to guard against 

negative obstacles forced a great amount of vigilance on the 

part of the user. Referencing back to the Hard Course, the 

site of greatest interaction besides stair climbing was driving off the curb slow enough to be safe. The autonomous 

behaviors could not identify the ledge as dangerous, so the 

user was forced to manually switch to teleoperation and 

drive off slowly. Only when safely down could the user 

switch back into an autonomous mode. 

6.2 Moving Obstacles

Since much of the navigation was on roads, the user 

needed to keep an eye on the traffic during autonomous 

drives. The robot could drive directly into the path of a car, 

not being able to calculate that the car was in fact in motion. 

There has been work on moving object detection with 

LADAR and with stereo vision [9,10]; incorporating this 

into obstacle avoidance algorithms is a critical next step. 

Street driving is the easiest of all autonomous traverses: 

relatively straight, on a solid surface, with few holes or cliff 

edges, and the few obstacles that exist are large (cars, 

trucks). This is where autonomy can shine, but without 

some form of moving object ODOA, the best autonomy will 

be able to aspire to is fewer user interactions, with no hope 

of reducing user attention. 

7. Conclusions

We did a series of experiments to quantify the effect of 

our system’s autonomy upon the amount of user interaction 

required. We did this to gain insight into where the system 

would need to improve to reduce the strain on the user. 

We found that great amounts of improvement could be 

achieved with the ability to command traverses effectively 

beyond the current field of view. On simple terrain this 

could lead to almost zero interaction necessary for hundreds 

of meters at time-- although for complicated terrain this 

would require a very clever path planner and state estimation accuracy beyond what is currently available. Reducing 

attention on top of interaction would require a robust negative and moving obstacle detection behavior. 

8. References 

[1] D. R. Olsen and Michael A. Goodrich. “Metrics for 

evaluating human-robot interactions”. Performance Metrics 

for Intelligent Systems Workshop(PerMIS), 2003. 

[2] M. Tambe P. Scerri, and D. V. Pynadath. “Towards a 

theory of adjustable autonomy”. Journal of Artificial Intelligence Research, volume 17,pages 171–228, 2002. 

[3] S.Tejada, E. Normand, and S. Sharma. “Virtual Synergy 

An Interface for Human-Robot-Agent Interaction”. Workshop on Humans and Multi-Agent Systems, 2003, 

[4] T. Frost, C. Norman, S. Pratt, and B. Yamauchi. “Derived Performance Metrics and Measurements Compared to 

Field Experience for the PackBot”. Performance Metrics for 

Intelligent Systems Workshop(PerMIS), 2002 

[5] D. Bruemmer, J. Marble, D. Dudenhoeffer, M. Anderson, and M. McKay. “Intelligent Robots for Use in Hazardous DOE Environments”. Performance Metrics for Intelligent Systems Workshop(PerMIS), 2002 

[6] M. A. Goodrich and E. R. Boer. “Model-based humancentered task automation: A case study in ACC system design”. IEEE Transactions on Intelligent Transportation, 

part A: Systems and Humans, Vol. 33, No. 3, May 2003 

[7] M. A. Goodrich and D. R. Olsen, Jr. “Seven Principles 

of Efficient Interaction”. Proceedings of IEEE International 

Conference on Systems, Man, and Cybernetics, October 5-8, 

2003, pp. 3943-3948. 

[8] J. W. Crandall. Towards Developing Effective HumanRobot Systems. M.S. Thesis, Brigham Young University, 

2003. 

[9] E. Prassler, J. Scholz, M. Schuster, D. Schwammkrug. 

“Tracking a large number of moving object in a crowded 

environment”, IEEE Workshop on Perception for Mobile 

Agents, Santa Barbara, CA, June 1998. 

[10] A. Talukder and L. Matthies. “Real-time detection of 

moving objects from moving vehicles using dense stereo 

and optical flow”, IEEE/RSJ Int’l Conf. on Intelligent Robots and Systems (IROS), Sendai, Japan, October 2004. 
A Mixed Initiative Human-Robots Team Performance Assessment System 

For Use in Operational and Training Environments 

A. Freedy, J. McDonough, R. Jacobs, E. Freedy, S. Thayer and G. Weltman 

Perceptronics Solutions Inc., Sherman Oaks CA 91423 

M. Kalphat and D. Palmer 

U.S. Army RDECOM-STTC, Orlando FL 

ABSTRACT 

Military forces of the future will use mixed manned and 

unmanned forces for a broad variety of functions. 

Measurement of overall effectiveness in these mixed initiative 

systems will be essential in order to achieve optimal system 

performance levels. Behavioral measures of both human and 

unmanned performance obtained in system simulations or in 

live exercises will be used to continuously diagnose 

performance and identify required areas of training 

requirements. Likewise, specialized training will be necessary 

in order to leverage the complementary cognitive functions of 

human and machine to forge fighting entities and units with 

capabilities superior to those of humans or machines in 

isolation. Our team is currently developing a Mixed Initiative 

Team Performance Assessment System (MITPAS) consisting 

of a methodology, tools and procedures to measure the 

performance of mixed manned and unmanned teams in both 

training and real world operational environments. The work is 

being performed under SBIR Phase I and II contracts 

administered by RDECOM/STTC, Orlando, FL. Our 

objective is to provide a scalable turnkey MITPAS software 

system integrated with simulation and training environments, 

utilizing COTS HLA data logging tools and containing 

protocols for evaluation of various manned/unmanned team 

configurations in selected event-based scenarios. This paper 

describes our in-progress development of a underlying MultiDimensional Performance Model, our preliminary MITPAS 

architecture and our Use Case Scenario based experimental 

and evaluation plan, as well as our ideas for future 

applications of the completed MITPAS. 

KEYWORDS: mixed initiative teams, human-robot 

performance assessment, robotic training systems 

1. INTRODUCTION 

Mixed initiative introduces a new and unique aspect to the 

psychology of team performance: the interaction of two 

cognitive systems -- human and autonomous unmanned robot. 

In addition to the critical performance factors associated with 

human teams -- which include information exchange, 

communication, supporting behavior and team leadership -- 

the mixed manned/unmanned team adds a number of 

challenging new dimensions. Foremost among these is the 

ability of the human team to manage, predict, collaborate and 

develop trust with unmanned systems that may sometimes 

exhibit fuzzy responses in unstructured and unpredictable 

environments [1] [2] [3] [4] [8] [9]. 

 

The critical challenge in our work has been to develop systemspecific measures of behavior on which to base assessment of 

the mixed initiative team performance. Such measures must 

be unique to the information and decision environment 

associated with human-robotic teams and to directly link 

together behavioral processes important to mixed 

manned/unmanned tactical outcomes. The measures need to 

provide feedback for skill improvement in collaboration as 

well as adaptation to stress and workload, and they should 

help define the training needs themselves. 

2. PERFORMANCE MEASURES 

Our work on the definition of relevant performance measures 

began with the realization that future unmanned platforms will 

have some capability to operate autonomously within the 

scope of their mission tasking, but will be continuously 

“commanded” by human operators who will each direct the 

activities of a number of robots. As more is learned about 

modeling human behavior, increased sophistication in 

autonomous operations by robotic systems can be expected to 

reduce dependence on human supervisory controllers. At 

today’s and the near-future state of understanding, however, 

certain functions are not well supported by automation and can 

be performed at a much higher level of competence by human 

beings in collaboration with the robotic entities. 

Accordingly, at the performance level there are new human 

factors issues that require new types of skills and training. 

These emerge from the nature of the robots as decisionmaking systems operating in uncertain, unpredictable and 

unstructured environments. The key new performance issues 

include: 

• Performing supervisory control of robots 
• Adapting to variations in the level autonomy the robots 

exhibit in response to environmental and task variables 

• Varying task allocation to exploit the distinct

advantages of the human and robotic component (e.g., a 

robot can endure long mission duration, survive better 

but may have only about 80% of human cognitive 

capabilities) 

• Monitoring of robots’ decisions and actions to maintain

to achieve transparency of robot actions 

• Overriding robot decisions and actions when necessary 

• Helping to solve problems and handle contingencies 

 Research performed to date on measurement of team

training performance has focused on both the individual and

team levels [5] [6]. It is recognized that while both process 

and outcome measures are essential, training feedback mainly 

comes from process measures. The guiding principles are: (1) 

measurement and remediation must emphasize processes that 

are linked to outcomes; and (2) Individual and team levels

deficiencies must be distinguished to support the instructional

process. In our view these principles are directly applicable to 

the manned/unmanned team with the addition of another level

in the team structure, which we term as the Collective 

Manned/Unmanned (CMU) level, and which represents the 

major new dimension that is added to the team task

characteristics and structure. Our selection of measuring 

instruments and speci-fication of associated measurement 

methodologies thus extends the individual-team matrix of 

Cannon–Brower [1] to include the present case of 

collaborative manned/unmanned teams. 

Figure 1 System Performance Model 

3. PERFORMANCE MODEL 

The basis of our MITPAS approach has been to develop a

Manned/Unmanned Team Multi-Dimensional Performance 

Model that captures the critical performance attributes of the

distinct human and robotic decision and control environment.

Figure 1 below provides an overview of the hierarchical 

structure of the Model’s performance dimensions. 

The Performance Model we are developing draws on four

separate research areas that have been pursued independently

in the past but which are being integrated in this project to

establish meaningful criteria of overall performance. These 

research areas are: 

• Psychology of Team Performance - Human team

performance measurement in C3 information environments, performance variables, training evaluation and

measuring team related expertise, management of

workload and stress. 

• Unmanned Systems - Principles of establishing

performance metrics for autonomous systems 

• Mixed Initiative Systems – Research and findings on

the critical variables which affect human decision and

control of autonomous systems 

• War Fighting Behavior – Observations and measurements of combat team performance in war fighting 

tasks C3 tasks 

We have integrated and adapted theories and concepts in these 

areas to processes associated with manned/unmanned team

performance and training. Most critical were variables

related to the decision making behavior of the unmanned

Human Team

Processes

Team Performance Team Performance

Human/Robot Team

Processes

Team Behavioral

Processes

•Task Allocation

•Collaboration

•Supervisory Initiative

•Monitoring Feedback

•Controllability

•Situation Understanding

•Shared “ Mental” Model

•Task/Team Ratio

•Mixed Initiative Efficiency

•UV Behavior Observe-ability

•Level of Trust ( Overrides)

•Behavior acceptance

•Robot/Human Coordination

UV Management and

Control Processes

MMea eassurureess o off PPeerrffoorrmmaancncee

Mission

Processes

•Battle Outcome

•Tactical Gains

•Resources cost

• Collective conformity

• Latency

• Decision quality

• Comparative performance

Variables

•LOA/ROA

•Training level

•Workload

•System Design

Variables •LOA/ROA

•Training level

•Workload

•System Design

MMeeaassurureess o off EEffffeecct

t

iivveenness ess

•Shar ed Mental Models

•Situation Awareness

•Communication

•Info Xchange

•Supporting Behavior

•Initiative / Leadership

•Stress adaptation

Human Team

Processes

Team Performance Team Performance

Human/Robot Team

Processes

Team Behavioral

Processes

•Task Allocation

•Collaboration

•Supervisory Initiative

•Monitoring Feedback

•Controllability

•Situation Understanding

•Shared “ Mental” Model

•Task/Team Ratio

•Mixed Initiative Efficiency

•UV Behavior Observe-ability

•Level of Trust ( Overrides)

•Behavior acceptance

•Robot/Human Coordination

UV Management and

Control Processes

MMea eassurureess o off PPeerrffoorrmmaancncee

Mission

Processes

•Battle Outcome

•Tactical Gains

•Resources cost

• Collective conformity

• Latency

• Decision quality

• Comparative performance

Variables

•LOA/ROA

•Training level

•Workload

•System Design

Variables •LOA/ROA

•Training level

•Workload

•System Design

MMeeaassurureess o off EEffffeecct

t

iivveenness ess

•Shar ed Mental Models

•Situation Awareness

•Communication

•Info Xchange

•Supporting Behavior

•Initiative / Leadership

•Stress adaptation
systems, such as behavior transparency to the human 

collaborators, human trust in robot decisions and human

abilities to synergize the autonomy of robots so as to add to

the capability of the total team. Issues such as behavior 

prediction, level of autonomy and acceptance of robots actions

have also been examined and identified for possible high 

impact variable on total system performance. 

In accord with this approach, we have created a preliminary 

System Performance Model which captures the critical 

performance attributes of the distinct process of behavior

composition environment. Our objective was to identify the 

dimensions of performance which contribute to effective 

outcomes of collaborative manned-unmanned tasks and, in

particular, to formulate measures to evaluate training in

processes that are unique to the collective team of humans and 

robots. Accordingly, we have built a taxonomy of specific 

processes which can be decomposed into explicit behavioral

objectives side-by-side with measures of effectiveness based 

on actual outcomes. Our focus is on process measures that are 

closely linked to outcomes, because it is these measures that 

will provide the feedback necessary for training. The three

levels of team processes critical to training evaluation and

remediation are: (1) individual human; (2) team human; and

(3) collective human/robot team. 

We decomposed the processes into these three levels and 

developed taxonomy of measures for each level. We narrowed 

the performance measures to the simplest factor structure that

adequately cover the dimension of teamwork as was found in

previous investigators [2]. The actual Performance Model will 

consist of a multi-dimensional task process performance 

schema which will (1) aggregate the performance measures at

each level, (2) provide for training feedback at each level, and 

(3) provide a multi-attribute discriminate function to

determine an overall level of proficiency as well as a “passfail’ score. The weights of the attributes will be established in

simulations in which the linkage between specific task

performance measures and outcomes can be estimated. There

are two main types of measures: Measures of Performance 

(MOP) and Measures of Effectiveness (MOE); these are 

defined separately below. 

 

1. Measures of Performance (MOP)

These are observable and derived measures of the operators’ 

task skills, strategies, steps or procedures used to accomplish 

the task. They consist of the cognitive and interactive 

processes of the individual and team in collaborating together

and controlling the robotic entities in a coordinate manner.

MOP evaluates the human factor involved in a complex 

system. MOP was divided into 3 distinct classes of processes 

dimensions:

• Human Team Processes - These processes represent the

dimensions of the human team interaction 

• UV Management and Control Processes - These

processes represent the tasks associated with real time

control and monitoring of the autonomous entities 

• Human/Robot Team Processes - These processes

represent the dimensions of the human interaction with 

the robotic elements 

2. Measures of Effectiveness (MOE) 

 

These measure the “goodness’ of the composed behavior in

quality and the execution of war-fighting tasks. MOEs are 

influenced by much more than human performance. These

measures also contain variance accounted for by system

design, the surrounding environment and luck [6]. The

measure consists of the following dimensions

• Mission Effectiveness - Observable measures of the 

success of the mission as determined by objective military 

criteria. 

• Behavioral Effectiveness - Measures of the dimension of

behavioral effectiveness of the system in the battlefield

 

We anticipate that only a relevant and/or application-specific 

subset of all possible performance measures will be used in 

the turnkey MITPAS because: (1) some of the measures may 

be correlated; and (2) the selected ones will require assurance 

of high diagnostic value, which is referred to as discrimination 

validity, in the particular situation. In our future laboratory 

tests we plan to reduce the possible set of measures to a 

manageable subset. 

4. MITPAS FUNCTIONAL REQUIREMENTS 

Our plan is to implement MITPAS as a turnkey software

package incorporating three major capabilities: 

• Tools to set identify and specify key events that must be

included in an exercise in order to stimulate execution of 

actions by participants that are the targets of performance 

measurements; 

• Tools to capture data during the conduct of the exercise,

including automated extraction from data loggers and

formats for observational inputs from observers and

controllers; 

• Analytical tools to combine the data collected and 

produce quantitative measures of the performance and 

effectiveness of the human-robotic team(s) being studied;

• Report generation tools to allow researchers and trainers

to produce diagnostic and prescriptive arrays of the 

analytic products. 

We will also build initial tactical and technical databases, 

using proposed FCS tables of organization and equipment and

similar documents from other UV programs, databases. 
Figure 2 below diagrams the MITPAS system and its place 

within the training and evaluation environments. The Figure

focuses on MITPAS as an adjunct to the existing distributed 

interactive training environment, specifically the OneSAF 

Test Bed (OTB), in which it will be developed and initially 

evaluated. Figure 2 also expands on the normal context

diagram conventions to include the internal components of the 

system as well, highlighting which components interact with

which outside entities. 

Figure 2 MITPAS Components and Context 

In its initial implementation the system will also serve as the 

environment in which candidate measures and metrics are

tested against actual exercise performance in experiments to

identify and validate those measures that are most correlated 

with and predictive of successful tactical performance and 

battle outcome. We will define the high-level system

functions in terms of Use Case Scenarios and Interaction 

Diagrams for the various types of users as well as for 

interactions between MITPAS and external systems, such as: 

• Military Instructors and systems performance evaluators 

• Unit commanders who assign and monitor mission status 

• System Designers and Planners 

5. MITPAS ARCHITECTURE 

In our planned future efforts we will complete and implement

the MITPAS software architecture, developing the interfaces 

with external systems and user interfaces to support 

identification of scenario requirements, selection of measures,

monitoring and data collection, and post-exercise review and

analysis. We will also develop the analytical engine within 

the software, and as the performance measurement algorithms

are developed they will be embedded in that component. The

development of components will be done iteratively, in a 

spiral development process, providing an early initial

capability for experimentation, and evolving as experiments 

yield more data about performance and system requirements. 

In brief, we will implement a MITPAS Prototype System that 

will: 

Battlespace

MITPA MIT S

Event Based

Scenario

Observer/Controller

Data Input

Observer/Controller 

Data Input

Performance

Measurement

Setup

U

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e

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U

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e

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I

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Performance Indicator

analyzer

Success Criteria

Analyzer

Performance

Report Generator

Performance

Report Generator

Performance

Computer

Scenario

Composer

Exercise

Data

HLA Data Logger Battle Master

MSDL Interface

DIS/HLA Network

ARTEPS

T&E Plans

Manned Simulators

Mission Planning

and Analysis Tools

Mission Planning

and AnalysisTools

• Provide a Core Infrastructure for measuring the 

performance of Mixed-Initiative exercises. The core 

infrastructure is designed to facilitate the rapid 

implementation of performance measurement and 

analysis algorithms as well as to enable integration 
with multiple heterogeneous simulation and test 

environments. 

• Implement the specific performance measurement

and analysis detailed for the scenario described in

this proposal using the Core Infrastructure 

Careful consideration will be given to allow the system to be

scalable and provide extensive integration capabilities to meet

evolving performance assessment requirement over the system

life-cycle. Critical to achieving these goals is the use of a 

modular component-based software architecture which

extensively leverages open standards and de-facto standard

best practices in distributed system development. 

Furthermore, the system will leverage established tools and

components which have emerged from prior DoD investment

in modeling and simulation as well as independently

developed tools for collecting and analyzing data for DIS and

HLA. Additional consideration will be given to developing

and emerging standards in the training and simulation

communities. In particular, the MITPAS Core Infrastructure 

will be designed to support the Test and Training Enabling

Architecture (TENA) under development for PEO STRI as a

product of the Foundation Initiative 2010. TENA provides 

significant improvements on HLA and is designed to be used 

with embedded training systems and in training ranges.

Figure 3 MITPAS Architecture 

Figure 3 shows the main MITPAS system architecture. The

system is comprised of the following core components:

• MITPAS Instructor Console – An application to set

parameters for a given Mixed-Initiative exercise as 

well as construct a scenario 

• MITPAS Instrumentation Run-Time API – A 

middleware toolkit with APIs in C and Java to enable 

rapid instrumentation of entities including C4I 

Systems, simulation systems, and embedded training

systems 

• HLA Data Logger Interface – A connection to an

existing data capture mechanism for capturing and 

managing data from an HLA data-stream

• MITPAS AAR Interface - An application which 

implements the analysis and reporting capabilities of

the system as well as invocation of Scenario playback

• MITPAS Augmented HLA FOM – Supports capture

of additional data such as human interaction events, 

MITPAS will require augmenting of a particular

HLA Federation Object Model to add the additional 

classes and interactions. 

6. Use Case Scenario 

We will use scenario-based training trials as the experimental 

paradigm to identify, refine and validate MITPAS measures.

Scenario-based training relies on controlled exercises, or

vignettes, in which the target training audience is presented 

with cues that are similar to those found in the actual task

environment and then given performance feedback. In mature

training environments such scenarios are developed using

training and doctrinal materials such as ARTEPS and Mission

Training Plans along with validated performance measures. In

the MITPAS project, however, the goal is to identify and 

validate measures for a type of unit that does not yet exist and 

for whom no training documents have been developed.

Accordingly, we have developed a baseline scenario based on:

MITPAS

Instructor Control Interface

COTS

Event

Based

Scenario

Composer

Performance

Measurement

Setup MITPAS Instrumented Entities

HLA

OTB/

OOS

Manned

Simulators

Embedded

Training

MITPAS

Run-Time API

MITPAS

Run-Time API

MITPAS

Run-Time API

COTS

HLA Data

Logger (S2Focus, hlaResult...)

Exercise

Data

MITPAS AAR Interface

Performance

Evaluation

Reports

COTS

Scenario

Playback

Robotic

Force

Control

MITPAS

Run-Time API

MITPAS Augmented

HLA-FOM

MITPAS Augmented

HLA-FOM

Tactical

Databases

Performance

Models

COTS External Analysis Tools

(Workload Analysis,

Activity Catalog Tool, ...)

• Examination of candidate performance measures 

• Study of the Future Combat System 2015 Unit of

Action Design

• Sponsor focus on countermine capabilities 

Our current MITPAS use-case scenario focuses on a platoon 

of a Reconnaissance Troop, reinforced with Engineers, which 

is escorting a convoy in an Iraq-like environment. The platoon 

employs UGVs, SUGVs, UAVs (Type 3), MULES and an

ACRV, which allows for representation of a wide range of 

robotic capabilities and supports experiments focusing on

soldiers controlling individual robots, on those controlling 

multiple homogeneous or heterogeneous robots, or on a leader

controlling mixed human and robotic elements. Our current

scenario requires subjects to deal with an improvised

explosive device, a traditional minefield, small unit enemy 

action, casualties, and maintaining communications. 

We are able to identify a set of critical control events within 

the MITPAS scenario that exemplify the type of mixed 

initiative performance we are trying to assess. In the future

these critical events will be further refined in cooperation with 

our RDECOM PMs. In addition, the final scenario events and

candidate performance measures will then mapped to each 

other to ensure that scenario execution will elicit the actions
that the measures require. Table 1 below shows an initial stage 

in the process, in which measures are mapped into scenario 

events based on the current findings. The purpose here is to

demonstrate the methodological approach, rather than provide

an exhaustive listing, which will form part of the planned 

future effort. 

Table 1 Scenario Events vs. Performance Measures

7. Criteria for Success

Our approach to establishing criteria of success will follow the 

concepts of the Army Training and Evaluation Program

(ARTEP), which is the cornerstone program of unit training. 

Each ARTEP consists of defined tactical tasks to be

performed under specified conditions to a criterion or

standard. To determine if the standard is reached, the ARTEP 

provides evaluators with a list of Task Steps and Performance 

Measures scored Go, No Go or Not Evaluated. The ratio of

subjective Go to No Go marks and the significance of each 

determine whether the performance standard has been met.

While the Rates have evolved over decades to capture

virtually all-relevant measures of performance with regard to

human collectives, collectives of humans and robots will 

demand the exercise of additional skills by the human 

elements. The robots’ decisions will not always be transparent 

to the humans. Human acceptance of these decisions will 

depend on understanding the robots’ capabilities and 

Phase I proposal and furtherer analysis validated its applicability and effectiveness. 

 

anticipate robot behavior. The approach was proposed in our

the individual performance measures into a 

. Let x be the pattern of performance measures 

x

We will aggregate

scoring criterion by starting with selected ARTEPS that can be

adapted to human-robotic collectives (using FCS training

studies as a guide) and adding additional measures such as the

ones discussed above. The single-score-for-a-single-task

methodology of ARTEP will be expanded to provide a single 

score for a collective patterns of tasks We propose a multidimensional criterion of performance success, P, that

combines the direct performance measures across the various 

experimental (robot system) variables, as described below: 

Situation 

Understanding

Controllability

Monitoring

Feedback

Supervisory 

Initiative

Collaboration

Task Allocation

Stress Adaptation

Initiative/ 

Leadership

Supporting

Behavior

Information 

Exchange

Communication

Situation 

Awareness

Shared Mental

Models

EVENT

x

x

x

x

x

x

x

x

x

x

x

x

x

6.b.1

x

x

x

x

x

x

x

x

x

x

x

x

x

6.b

x

x

x

x

x

x

6.a.1

x

x

x

x

x

x

x

x

x

x

x

x

x

6.a

x

x

x

x

x

x

x

6

x

x

x

x

x

x

x

x

x

x

5.b

x

x

x

x

x

x

x

x

x

x

x

x

x

5.a

x

x

x

x

x

x

x

x

x

x

x

x

x

5

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x UV Mgmt and 

Control

Processes

x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x Human Team

Processes

1 1.a 1.b 2 2.a 2.a.1 2.b 2.b.1 3 3.a 3.a.1 3.a.1.a 3.a.2 3.a.2.a 3.b 4 4.a 4.a.1

MEASURE

Situation 

Understanding

Controllability

Monitoring

Feedback

Supervisory 

Initiative

Collaboration

Task Allocation

Stress Adaptation

Initiative/ 

Leadership

Supporting

Behavior

Information 

Exchange

Communication

Situation 

Awareness

Shared Mental

Models

EVENT

x

x

x

x

x

x

x

x

x

x

x

x

x

6.b.1

x

x

x

x

x

x

x

x

x

x

x

x

x

6.b

x

x

x

x

x

x

6.a.1

x

x

x

x

x

x

x

x

x

x

x

x

x

6.a

x

x

x

x

x

x

x

6

x

x

x

x

x

x

x

x

x

x

5.b

x

x

x

x

x

x

x

x

x

x

x

x

x

5.a

x

x

x

x

x

x

x

x

x

x

x

x

x

5

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x x x UV Mgmt and 

Control

Processes

x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x x

x x x x x x x x x x x x x

x x x x x x x x x x x x x Human Team

Processes

1 1.a 1.b 2 2.a 2.a.1 2.b 2.b.1 3 3.a 3.a.1 3.a.1.a 3.a.2 3.a.2.a 3.b 4 4.a 4.a.1

MEASURE

1

, , , , ) j 1 j 2 j 3 j nj x = ( x x K x

under the various cond

tc marked by the subscript j

itions, 

i.e. level of automation, stress, e

The multi-attribute performance score for condition j is: 

j 1 1 j 1 2 j 1 3 j n nj g(x ) = w x + w x + w x +K+ w x , 

thus 

∑=

=

n

i 1

j i ij g( x ) w x
2. To get a total score cross all conditions the combined 

score is 

∑=

m

j 1

j g(x )

3. The combined aggregated score for all performance 

measures and condition will then be: 

 Total Score ∑∑= =

=

m

j 1

n

i 1

i ij P w x

4. The weights will be determined by

testing experiments and expert judgment using a

parameter estimation protocol of the type used in

trainable pattern recognizers. 

( , , ) w1,w2 K wn

We have developed a schema employing a factor analytic

approach to reducing and refining the set of measures to 

reflect underlying orthogonal performance dimensions [7].

This strategy will be employed using a virtual battlespace to 

collect data for analysis.

The scenarios, candidate measures and algorithms, and the 

OTB V2.0 virtual testbed provide a framework for a multistage data collection effort within which soldiers with 

representative background, experience, training, and skill 

levels will be asked to execute FCS missions as part of a 

human-MULE robot team. After a verification and validation

effort to ensure that the test software produces the intended 

data products, mission trials will be conducted in which 

soldiers will team with robots to perform specific assignments 

within the exercise scenarios. The simulation, instrumented 

with the selected data extraction and analysis tool, will 

produce measure data for each of the candidate measures

constituting the independent variables. 

Dependent variable data will come from a different source. 

The Objective Force combat development community will be

asked to provide subject matter experts to observe the trials

and to provide subjective evaluations of the execution of the 

human-robot team. Accepting the expert judgment to be the

reference standard for performance evaluation, the factor

analysis process will be employed to examine the value of the

component and composite linear factor combinations of the 

candidate measures in accounting for observed performance.

The intent is to seek to identify a reduced set of orthogonal 

underlying composite measures to which a practically 

substantial proportion of the measure variance (in relation to

expert subject judgment) can be allocated. Conceptually, the 

process can be thought of as a rotation of the principal 

variable axes within the data space to identify a new 

coordinate set that minimizes the data variance. The rotated 

axes are linear combinations of the original set, and 

correspond to underlying variable factors suggested by the 

distribution of the data in the variable space. Factor analysts 

often look upon this as “first-stage solution” and will typically

follow this with further non-orthogonal rotations to achieve

what they call a “simple structure”. For our purposes 

however, this will not be advisable, as non-orthogonal rotation

has implications to the independence, transformation, and

scaling of the data. 

8. Experimental Plan 

Our planned experimental test program is structured in four

parts. Following is a preliminary description of each phase;

the detailed test design will be produced during the 

requirements development effort. 

1. Laboratory System Pilot Runs 

In the first phase, the test environment will be set up and 

validated. Pilot runs will confirm that the measurement 

algorithms are functioning correctly, that the scenario is 

properly simulated, that the participating virtual platforms and 

behaviors representations are valid, and that the human 

operator interface is fully functional. Pilot runs will be 

conducted to confirm that the design is fully responsive to the 

requirements of the program.

2. Model Validation and Tuning

The second phase will be devoted to collecting data across the 

spectrum of operations in the scenario, expert observation and

evaluation, and reduction of the measure set through factor 

analysis. The focus will be on the simplest form of humanrobot team, a single operator supervising the activities of one

or two robots. The scenario will be executed in the context of

FCS embedded individual training with an emphasis on what

might become ARTEP/Drill tasks for the human-robot team. 

3. Battle Operations in Simulation 

We will validate the reduced measure set by applying it to a 

more complex set of activities representative of FCS 

battlespace operations. The scenario will involve sequences 

of the types of tasks that formed the focus for phase two, and

it will be executed by a small team consisting of two or more 

human operators and several virtual robots. This will

introduce the dimension of collaboration and allocation of

responsibilities to the scenario execution. 

4. Field Operation with Live UVs 

As an option, we propose in a fourth phase to demonstrate the 

operation of the performance measurement system in a live
simulated environment using instrumented UVs operating on a 

tactical range. 

9. Conclusions 

The key challenge being addressed in this project is the fact 

that autonomous vehicles, or agents, will need to interact and 

coordinate with each other and with human systems. 

Measurement of overall effectiveness in these mixed initiative 

systems will be essential in order to achieve optimal system 

performance levels. Behavioral measures of both human and 

unmanned combat system (UCS) performance obtained in 

system simulations or in live exercises will be used to 

continuously diagnose performance and identify required 

areas of training requirements [3]. 

Likewise, specialized training will be necessary in order to 

leverage the complementary cognitive functions of human and 

machine to forge fighting entities and units with capabilities 

superior to those of humans or machines in isolation. 

Embedded training is also projected to be an important part of 

the Future Combat System (FCS) to assure that performance 

levels remain high during all operational phases. Overall, a 

clear and definite need exists for methods and mechanism to 

assess and determine criteria for successful performance of 

unmanned systems and manned/unmanned teams in both 

training environments and the real warfighting situations. 

We believe that meeting this need will also lead to significant 

commercial product opportunities in the large and rapidly 

expanding military and non-military markets for robotic 

systems. The focus of our SBIR commercialization strategy 

will be transformation of the MITPAS prototype into a suite of 

software modules for use in a variety of mixed initiative and 

mobile agent applications. The software product will be 

optimized to meet military and non-military market 

requirements. It will be sold and/or licensed to DoD and 

Homeland Defense agencies and prime contractors, to civil 

organizations that employ remote human controlled robotic 

agents and unmanned vehicles in hostile environments and for 

counter terrorism activities and local law enforcement, and 

also to companies manufacturing and distributing industrial 

and personal robots. In addition, we plan to explore in Phase 

the application of the MITPAS as a commercial tool for 

helping military and non-military emergency response teams 

determine when and how to use mixed initiative teams on a 

particular type of mission, e.g., in a bomb disposal situation. 

10. References 

[1] Fong, T., Thorpe, C. and Baur, C., “Collaboration, 

Dialogue and Human Robot Interaction.” Proc. 10th

International Symposium on Robotic Research, Spinger 

Veralng, 2002 

[2] Fong , T., Kaber, D, Scholtz, M.L. , Shultz, A. and 

Steinfeld, A., “Common Metrics for Human-Robot Interaction” IEEE International Conference on Intelligent Robots 

and Systems, Sendai, Japan, 2004 

[3] Kalphat, H. M., and Stahl, J., “STRICOM’s Advanced 

Robotics Simulation STO: The Army Solution to Robotics 

M&S,” Proceedings of the Eleventh Conference on Computer 

Generated Forces & Behavioral Representation, Orlando, FL, 

May 2002. 

[4] Cannon-Bower, J.A. and Salas, E., “Individual and Team 

Decisoio Making Under Stress: Theoretical Underpinning” in 

Making Decisions Under Stress, (Ed) Cannon-Bowers, J. and 

Salas E., American Psych. Assoc., WDC, 1998 

[5] Singh, P.N, Thayer, M.S., “ARMS: Autonomous Robots 

for Military Systems, A Survey of Collaborative Robotic Core 

Technologies and Their Applications,” CMU–RI-TR-16, 

DARPA Project Report, 2001 

[6] Smith-Jentsch, K.A., Johnson, J.H. and Payne, S.C., 

“Measuring Team Related Expertise in Complex Environments”, in Making Decisions Under Stress (Ed) CannonBowers, J. and Salas E., American Psych. Assoc., WDC, 1998 

[7] Tatsuoka, M.M., Multivariate Analysis, Techniques for 

Educational and Psychological Research, John Wiley & Sons, 

1971 

[8] Albus, J.S., “Metrics and Performance Measures for 

Intelligent Unmanned Ground Vehicles” PerMIS Proceedings, 

2002 

[9] Clough, B.T., “Metrics, Schmetrics! How the Heck Do 

You Determine an UAV’s Autonomy Anyway?” PerMIS 

Proceedings, 2002 

11. Acknowledgements 

1. The work reported here was funded under Contract No. 

N61339-04-0020 administered by US Army RDECOMSTTC, Orlando, FL 

2. Dr. Robert Jacobs serves as a staff member of the Institute 

for Defense Analysis, Alexandria, VA 

3. Dr. Scott Thayer serves as Systems Scientist in the 

Robotic Institute at Carnegie Mellon University, 

Pittsburg, PA 

4. Michelle Kalphat serves as Chief Engineer, Intelligent 

Behaviors for Autonomous Systems & Simulation 

Technologies, US Army RDECOM-STTC, Orlando, FL 

5. Donnie Palmer serves as Computer Scientist, Intelligent 

Behaviors for Autonomous Systems & Simulation 

Technologies, US Army RDECOM-STTC, Orlando, FL 
BIOLOGIZING CONTROL SYSTEMS

Paul Wang

Duke University

Durham, NC

ppw@ee.duke.edu

Abstract

One of the most important performance metrics for a control system is the reliability. To

accomplish this objective, some intelligent controller must be developed. Relevant

theory on this line has been von Newmann's cellular automata theory.

However, von Neumann's theory of cellular automata is not general enough to realize the

'biologizing” of control systems. Furthermore, the non-autonomous responses must be

studied in order to realizing the truly reliable system via self-organizing schemes. This

paper presents both new features.
ENTROPY AS A PHILOSOPHY

George N. Saridis PhD

Dedicated to Ilya Prigogine

PREFACE

The ancient Greeks considered philosophy as the mother of sciences engulfing the essence of all

human achievements. It is therefore, natural to associate her with elements of universal scientific

developments. The intention of this article is to present the current point of view of the situations

governing our planet, our societies, our environment, and attempt to foresee their future

developments. Entropy, the thermodynamic measure, is an analytic tool that may serve to evaluate

phenomena that dominate our lives, and therefore belongs to the realm of philosophy. Since the

trends show a universal trend for equalization, like the concepts of codification and globalization, an

increase in global entropy is appearing as an obvious result. Is this going to create an “equivalent

thermal death” to our planet? Is there a cure to this phenomenon? The recently developed theory of

Chaos, introduced by Ilya Prigogine gives us some hopes for a possible redemption of this

catastrophe. This will be discussed scientifically in the sequel, by considering the various elements

of our present situations.

1. INTRODUCTION

The creation of the Universe and the mystery of life

have always been problems puzzling the philosophers.

Technological progress and the increasing knowledge

of the elements of the environment have not

considerably improved their beliefs. With the years a

feeling of uncertainty about the Universe and the

human existence has been generated and recently has

become more pronounced.

Young people ask questions about God, our past and

future existence and in general, how much control we

do have on our lives and our environment. The world

exists the way we see it and the models we have

produced are inadequate to generate any positive

answers. This creates a chaotic situation in the minds

of the thinkers, desperately trying to create a viable

model of the world that explains the past and predicts

the future.

Since the early days, when human thought was

developed, many attempts were made to systematically

formalize the human activities in the Universe.

Biological, Societal, Religious, Scientific, and

Legalistic theories, to mention a few, were created

independently; to model and represent the world we

live in. Most of those were dealing philosophically

with believes, that were created by the people in the

form of irreversible phenomena.

Philosophy was always the main source and

foundation of progressive theories. Ancient Greeks

considered it as the mother of all sciences. It was

always considered as a source of global energy. The

historian Thucydides said “filokaloumen met 

eiaz kai losojoumen aaneu malakiz. ” It is

the ground of development of clear modern thought

both scientific and literary. It is in this aspect that will

be used in the present document to describe our world.

In our days with the development of computer science

scientists from different areas were able to

communicate with each other end establish analytic

models that approximate the behavior of various

phenomena to the degree that we presently understand

them. Therefore we hear biologists talk about models

of DNA, ecologists about models of the environment,

sociologists about globalization, thermodynamisists

and mechanists coordinating their efforts, and so on

and so forth. Analytic approaches to describe human

activities appeared also in the world of literature. Such

models, still at a primitive stage, are considered around

the equilibrium of each process, and obey certain laws

that are emanating mainly from physics, the science

that started it all.

There is a notion of pessimism in this approach

generated by the second axiom of thermodynamics

where entropy invokes the thermal death, for all

natural activities. Is this argument valid or it is

assumed due to the closeness to the natural

equilibriums? May be when we move away we may
encounter a regeneration the way that Prigogine

proposes with his theory of Chaos. There is still hope

for our world.

However, little has been devoted to the concept of

energy as the source of generation of such activities.

Entropy, an irreversible source of energy, that like life

itself, looks like a strong candidate to describe the

phenomenon of the Universe and belongs to the

philosophical framework. This claim is also justified

by the conditions of disorder and tastelessness that

exist in the modern world. This of the entropy

formulation will be elaborated in the sequel.

2. WHAT IS ENTROPY

In the modern times one may extend the concept of

philosophy to cover entropy, the low level energy,

which results as a terminal by-product of any kind of

effort created in most cultures. Entropy has been

defined as the residual irreversible energy generated in

thermodynamics (Boltzmann 1872), and has been

extended by Prigogine (1980,1996), Saridis (1995) et

al (1988,1957), to denote the energy of the

probabilistic view of the world. Such a concept is very

popular in modern science, and expresses the

uncertainty of the model of the world we have created.

Since the idea of a probabilistic world is generic, with

an “arrow of time pointing forward” (Coveney and

Highfield 1990), it may cover most cultural activities it

may also be interpreted by a Global Philosophy.

For centuries scientists theologians and sociologists

were arguing that the world is deterministic. “There is

always a beginning and an end of the world” they

said, in an anthropomorphic way, since life has a

beginning and an end. This includes the modern theory

of the “Big Bang” as the creator of the universe.

However, life and the world in general, represent

irreversible phenomena. Without trying to interpret

dogmatically metaphysical phenomena, scientists tried

to build analytic models of the existing world and

found only crude approximations to match reality. The

alternative was the assumption of a probabilistic

description that fitted best the data.

The physicist Clausius discovered this low quality

energy, which appeared in the second law of

thermodynamics and was named Entropy. According

to this law the production of work is followed by the

production of residual energy that irreversibly

increases the total level of the lower quality energy of

the world. This phenomenon would lead to the

exhaustion of the useful energy, preventing the

creation of new useful work, thus creating a thermal

death of the world. Boltzmann used entropy to study

the behavior of gases (Boltzmann 1872, Prigogine

1996).

Entropy was given a different interpretation of by

Claude Shannon (1963), as a measure of uncertainty in

information theory related to telecommunication

systems. This interpretation was used by Saridis

(1995), to introduce a theory presenting Automatic

Control as a generalization of the theory of entropy,

based on the designer’s uncertainty to obtain the

optimal solution. This concept is hereby extended to

cover subjects related to the environment, finances,

pollution and other problems that puzzle our present

society.

3. FOUNDATION OF AN ENTROPY MODEL

The contribution of this work is the introduction of

uncertainty to the Universe, and to effectively restrain

the growth of the Global Entropy, created by the

human intervention with the environment. Since the

text is addressed to the unspecialized reader, an

attempt will be made to introduce first the probabilistic

concepts of our cultural systems.

It is not the intention of this effort to challenge the

question if the world is either deterministic or random.

Instead in my opinion it recognizes that the models we

use to represent it are uncertain, being only an

approximation of the real world. It is well known that

“Mother Nature does not read mathematics”.

The model of the world I propose is based on the idea

that the world lives in an uncertain space of

approximations, where every point is assigned a

probability of success based on some performance

criterion. The selection of the appropriate model is

based on the point in space of highest probability.

Modern technology, has greatly contributed to the

improvement of the quality of human life, and to

explain various phenomena of our cultural

environment. At the same time, it has increased the

production of waste, traffic congestion, biological

pollution and in general environmental decay, which

can be measured by the increase of the Global Entropy

of our planet, an energy that tends to deteriorate the

quality of our environment (Brooks and Wiley 1988,

Prigogine 1980, Rifkin 1989). This entropy, in

agreement with the arrow of time, is modeled

according to the second law of thermodynamics, which

is an irreversible phenomenon of generation of low

quality energy.

The original idea of using entropy to describe the

deterioration of the quality of energy, when useful
work is produced, is due to Boltzmann with his

monumental work in statistical thermodynamics

(Boltzmann 1872). Shannon {1963) followed with the

introduction of entropy in his information theory.

Accordingly, Brooks and Wiley (1988) recommended

entropy as the unifying theory for Biological

Evolution, and Rifkin (1989) suggested the use of

entropy to measure the production of waste in

environmental systems. This concept is utilized in this

paper in order to manage its component due to human

functions.

Saridis, using Janes’ principle of Maximum Entropy

(1957), formulated the engineering design problem as

a problem with uncertainty, since the designer does not

know a-priori the outcome of his design (Saridis

1995). Entropy was used as the measure of the energy

associated with the assumption of irreversibility of the

process. This way the optimal control problem was

recast as an entropy minimization problem and the

known expressions were reproduced.

In addition Saridis, working on the problem of

reducing analytically the increase of entropy generated

by human intervention in global systems, added an

extra term to the equation of work producing systems,

and used optimal control to minimize the effect of the

resulting entropy. The combination of the two

approaches produces an analytic method of reducing

the part of global entropy due to human intervention

with the environment.

4. THE PROBABILISTIC VIEW OF THE

WORLD

A formal presentation will be made, of the

probabilistic approach developed from an entropy

point of view, and thus present a method to minimize

its effect to our cultural systems. This theory has in

addition to the practical applications, a philosophical

foundation that has implications to the quality of life

and the future of our planet. Experimental results are

due after the collection of data from environmental

systems.

Global Entropy, associated with irreversible

phenomena, appears when we consume energy in order

to accomplish some work in our environment we

simultaneously create a low quality residual energy,

that irreversibly reduces the quality of the environment

and leads to a chaotic situation. An infinite number of

paradigms exist in our environment, starting with the

pollution of the air and the water resources, increase of

the waste areas, traffic congestion, financial disasters,

unemployment with the resulting crime, and in general

the decay of the life-sustaining resources of mankind

(Prigogine 1980).

Entropy in our cultural environment has been

introduced through our modern technologies, as an

energy producing work, like the latest major

improvements in the average quality of life. These are

producing major increases in the production of waste,

traffic congestion, biological pollution and in general

environmental decay, which can be interpreted as the

increase of the Global Entropy of our planet, an energy

that tends to deteriorate the quality of our present

environment. According to the second law of

thermodynamics this is an irreversible phenomenon,

and nothing can be done to eliminate it. Brooks and

Wiley suggested entropy in Biological Evolution

(1988), while Rifkin used entropy as the measure of

decay (1989), and Faber et. al. (1995) propose Entropy

for Economic systems. However, other major cultural

areas of thought, like societal systems, religion, legal

and governmental theories have not kept up with the

technological achievements, and therefore are missing

in benefits due to the lack of appropriate models for

their study. The theory of Entropy, if introduced

properly, in addition to its practical applications, has a

philosophical foundation that has implications to the

quality of life and the future of our planet.

There exists a huge literature with analytic

formulations of the problems that concern modern

societies, like ecology, environment, biochemical

systems, econometrics, and other applications. A good

summary of those systems can be found in Singh’s

Systems and Control Encyclopedia (Singh 1987)

which served as a source for the development of the

material associated with the application of Optimal

Control for the reduction of the Global Entropy

generated by the work produced by humans in order to

improve the quality of life.

The analytic models considered here are for;

Art

Biological Systems

Biochemical Systems

Ecosystems

Engineering Systems and Manufacturing

Environment and Pollution

Phenomena in Modern Science: The Universe

Religion

Socioeconometric and Political Systems

Societal Systems

In most of these cases, the models have been modified

to introduce the human effort as a random control

variable to be optimized. Such an approach presents as
a solution the possible improvement of the problem of

decay. These models may not be the most general or

the most popular ones, since controversies exist among

the various researchers, however they are

representative to demonstrate the idea of improving the

quality of our world by reducing the entropy generated

by the work produced.

5. “CHAOS” AND THE WORLD DYNAMICS

AWAY FROM THE EQUILIBRIUM.

Assuming the analytic model for human activities, the

theory of Chaos, or the dynamic behavior of nonlinear

dynamic systems away from the equilibrium,

developed by Pigogine for biosystems originally, came

to assist modern scientists to expand the analytic

concepts to other cultural phenomena.

From their primitive years, humans have tried to

understand and formalize the world around them,

through the sensors that nature provided them. To do

this they have used various models to represent

“approximations” of the functions of the world. They

separated those functions into two categories governed

by:

1. The Physical Laws of Nature describing

deterministic physical phenomena, and

2. The Behavioral Laws describing nondeterministic organic, environmental and

societal phenomena.

For the first class, linear mathematics proved to be a

concise methodology to approximately describe the

time-reversible results of physical experiments near

their equilibrium. Logical (Aristotelian) analysis and

statistical exhaustive search, were the methodologies

used to classify and study the evolutionary behavior of

living organisms, environmental and ecological

changes and societal phenomena that demonstrated

time-irreversibility known as the arrow of time

(Brooks and Wiley 1988, Prigogine 1989).

In the recent years, with the progress of the

mathematical science and the development of digital

computers, probabilistic and stochastic methods and

analytic logic are replacing statistical aggregation and

classical logical analysis in the realm of mathematics

to describe the world’s phenomena. Linear analytic

models were assumed to be sufficiently accurate to

represent useful models of this world, as viewed by

human senses. “Reductionism” that has been a

powerful tool to analyze and predict physical

phenomena, was promptly extended to cover natural

phenomena for description and prediction of their

behavior. The deterministic model evolved on the

principles of the Newtonian mechanics.

However, there were cracks in this wonderful and

supposedly airtight, reasoning system. Physical

discrepancies and analytic paradoxes marred the

perfect models that the world thought infallible. One of

the major difficulties encountered was the gap between

Newtonian mechanics and thermodynamics. Scientists

discovered that heat was produced by the collision of

millions of particles in a perfect gas, generating

irreversibly entropy, a lower level of energy. However,

Poincare showed, that it is practically impossible to

study the motion of more than three bodies and thus

understand the process. Boltzmann(1872) bridged this

gap by introducing statistical methods to describe

kinetic phenomena and equate their average kinetic

energy with entropy. This pioneer work showed a way

to model uncertain and complex physical phenomena

in continuous time and connected them to irreversible

evolutionary models described by Darwin (Brooks and

Wiley 1988), and Shannon (1963) followed with his

celebrated information theory.

Prigogine (1989) after observations on biochemical

phenomena, studied the behavior of dynamic systems

away from their equilibrium, a procedure which led to

their nonlinear behavior. Jump phenomena led to

possible nonunique alternate situations that would

converge to a static equilibrium with linear behavior.

Therefore, it explained the unrealistic transition from

order to disorder as interpreted by the disciples of

determinism. This originated the theory of Chaos

proposed by Prigogine.

Saridis (1995), in the meanwhile, using Jaynes’

principle (1957), formulated the engineering design

problem as a problem with uncertainty, since the

designer does not know a priori the outcome of his

design. Entropy was used as the measure of the energy

expressing the cost of the irreversible associated

process. Considering control as the work and entropy

as its cost, the optimal control problem was recast as

an entropy minimization problem and the known

expressions were reproduced. The cost of the

reliability of the design was also expressed as entropy,

and was considered as a natural extension of the

proposed theoretical development.

Major problems regarding the completeness,

consistency and decidability of a statement in a

discrete event space, arose with Gödel’s theorem of

undecidable statements that limited the use of digital

computers for the analytic solution of complex

problems. Such problems existed with the Diophantine

equations and other paradoxes but they were swept
under the rug, so that they would not challenge the

power of the computer. Such problems were remedied

by introducing new quasi-statistical engines like

artificial intelligence, fuzzy set theory and other such

techniques. All those problems were blamed to the

inadequacy of linear models, and the complexity of

systems operating away from the equilibrium point

like most of the biological, environmental and societal

systems do. Thus, the theory of Chaos was introduced

by Prigogine (1996) to study and analyze such cases.

The benefit of these discoveries was that complexity

and undecidability brought all these problems together

and global formulation of their solution was sought.

Uncertainty, which is indirectly associated with time

irreversibility, was the common element representing

the doubt of the outcome of such systems, and

stochastic approaches were introduced which have

entropy as a common measure.

Thus, the uncertainty of modeling of complex systems

is the reason of introducing entropy, in Shannon’s

sense, as a measure of quality of large complex

continuous or discrete event systems. In essence, since

entropy is energy irreversibly accumulated when work

is performed, and originally introduced in

thermodynamics, it is generalized to any kind of

dynamic system appearing in nature. Therefore,

entropy measures the waste produced when work is

done for the improvement of the quality of human life,

the struggle of the species in an ecosystem, the

biological reactions of a living organism, even the

politics of in a societal system. Entropy assumes a

stochastic model with uncertain outcome, which is

suitable to describe the new complex model of the

world.

The theory also gives us a hope that there may be a

way out of the accumulation of entropy which may

lead us to the thermal death.

The question now is if and how this model and the

underlining systems, can be improved, by reducing the

waste of energy represented by entropy, using analytic

methods. Concepts from control theory, used the

introduction of a control term in the analytic model,

has been proposed to solve this problem.

6. APPLICATIONS

6.1 Biochemical Systems

Prigogine(1980) in his work “from Being to

becoming” identifies chaotic phenomena in certain

biochemical reactions away from their equilibrium.

Since these reactions are irreversible he characterized

them with lower level Entropy. Experiments like the

Belousov Zhabotinskii have established the value of

chaotic behavior of chemical reactions.

6.2. Biological Systems

Biological systems produce work through their

lifetime. This generates Entropy expressed by the

energy of decay of the system. Aging and the

deterioration of the human body, diseases and organic

decay are typical examples of various forms of

Entropy. Medicine has being struggling to reduce their

effect by optimizing the duration of human life.

Scientists in Biology stared understanding the models

of DNA and are simulating them on digital computers.

The resulting models, although primitive are

attempting to construct and explain the structure of

living organisms. DNA is a map of human heredity.

Cloning, with the use of DNA has been used for

biological preservation. Transplants are typical

examples of an optimal control process. They may

represent alternate solutions related to Chaos. This

gives us hope of reduction of the biological Entropy.

6.3 Ecosystems

The energy produced by the work of living organisms

generates Entropy in the form of decline of

reproduction of species and the decay of their

environment. This may be measured analytically, by

the entropy which expresses the irreversible residue of

low level energy. The phenomenon of such devastation

is obvious in the environment which is full of waste

dumps and barren land where various endangered

species used to live. It is really heartbreaking to look at

lands, which were full of life and energy to appear

barren and desolate. The plants are replaced by waste,

the living creatures are gone forever and the ponds

have turned into swamps. Wetlands are filled with

poisonous waste, while floods take place due to

constructions in ravines. There is of course recycling

as a control measure of the environment. However, this

is only a temporary

solution since the total entropy of the system still

increases even at a slower rate.

As mentioned above, Saridis (1998) working on the

problem of reducing analytically the increase of

entropy generated by human intervention in ecological

systems, added an extra term to the equation of

ecosystems and used entropy formulation of optimal

control to minimize its effect. However, this is only a

temporary solution and not an answer to the question.

The problem is devastating since, as they used to say,

there is no more room “to go West” to conquer new
land. There is of course the outer space to go and

pollute, but this technology is still many years away.

6.4 Entropy and Religion

Religious fanaticism is a scheme that produces

pointless work. As a result it generates material

destruction, mental agony, pros elitism and contempt

to human life all variations of mental Entropy. This

phenomenon has existed throughout the centuries as a

by-product of human weakness to face the realities of

the world.

There is a revived effort by the clergy of all

persuasions to attract and proselytize more faithfuls

with after life promised rewards. Absolute

brainwashing with dogmatic overtones has been

demonstrated all over the world, especially in the

Moslem religion. Kamikaze bombers have created

religious terrorism. The value of human life is thus

reduced by the promise of sanctitude. “Religion is the

opium of the world” said Karl Marx.

The problem is not a privilege of Islam. Other

religions, including Christianity, are encouraging low

level emotions. Masses are drawn to hysteria in order

to chase away the scare of death. Buddhism is an

exception to such a craze.

Unsuccessful attempts to equalize various religions,

e.g. Christianity, help to increase the entropy of belief.

Could the theory of Chaos if applied, relieve humanity

of such a disaster?

6.5 Entropy and the Society.

Modern society is getting more structured and more

dynamic. On the other hand, ethical and moral

deterioration is getting more pronounced in our present

days. A formal presentation of an entropy theory to

describe the ethical and moral decay of our times is

considered. It is developed from an entropy point of

view that relates optimal control theory to the Global

Entropy, and thus represents a method to minimize its

effect to our society. This theory has in addition to the

practical applications, a philosophical foundation that

has implications to the quality of life and the future of

our planet. Experimental results substantiate this

theory.

Since the urbanization has dominated our social

dynamics the lowering of the quality of our societies

has begun. Migration of the members of the poorer

societies to the richer ones have been the cause of this

deterioration by introducing lower quality life in

congested neighborhoods, and cheaper workforces

which lower the Entropy of the system.

The decay of the family ties is characteristic of the

modern society, due to busy parents. Their lack of

generates loneliness and anxieties to both the parents

and their children. Stress appears as a result which

leads to drug addiction and suicide of the young

people. The multimedia contribute more to the decay

of family life.

The newly introduced concept of globalization, which

intends to decrease the gap between rich and poor

societies, may be viewed as a method of equalizing

resources of the world thus increasing its total Entropy.

Further more it exploits the working class by

monopolizing the marketed products.

6.6 Entropy and the Art.

Entropy measures the residue energy of generation of

the atrocious modern art of our times. The age of

cheap and bad taste for painting, sculpture, literature,

clothing and other forms of art has been dominant.

Paintings like the ones produced by a well known

modern Greek painter, the 2004 Olympic mascots,

sculptures like the moving part ones or made of scrap

metals and literature like the trashy memoirs of the so

called celebrities of the year, are tasteless products of

our times.

Music like “rap” which replaced jazz in the black

culture, the screechy singers and the “meowing”

bimbos on the stage are another example of the

lowered quality of art. Meaningless songs are filling

the air. Baggy trashy clothes that the modern artists of

the stage and fashion show models are wearing are all

cheap and tasteless.

Their low quality taste, are Kitsch which represents

the new form of Entropy in modern Art.

6.7 Environmental and Pollution

The energy of accumulation of pollutants in the

environment and its decay is next in the list of entropy

generating agents. Poisonous chemicals, nonbiodegradable plastic products, nuclear waste, are

accumulating on our lands and seas that kill life

producing organisms and are emasculating Mother

Nature.

Modern technology has greatly contributed to the

improvement of the quality of human life. At the same

time, it has increased the production of waste, traffic
congestion, biological pollution and in general

environmental decay, which can be measured by the

increase of the Global Entropy of our planet, an energy

that tends to deteriorate the quality of our environment.

Accordingly, Rifkin (1989) suggested the use of

entropy to measure the production of waste in

environmental systems. This concept is utilized in this

work in order to manage its component due to human

activities.

Entropy was used as the measure of the energy

associated with the assumption of irreversibility of the

process. The methodology of using Entropy with

Automatic Control, produces an analytic method of

reducing the part of global entropy due to human

intervention with the environment. Again Saridis’

approach to minimize their effect through analytic

optimization methods is not sufficient to eliminate the

problem. As in the ecosystem description one has to

think of moving to other planets to find clean

environments.

This approach contributes to the introduction of the

entropy approach of optimal control theory, to

environmental systems, to effectively restrain the

growth of the Global Entropy, created by the human

intervention with the environment.

6.8. Manufacturing and Engineering Systems

The evolution of the digital computer in the last thirty

years has made possible to develop fully automated

systems that successfully perform human dominated

functions in industrial space, generating waste

interpreted as entropy with automation as a major

factor in modern technological developments. It is

aimed at replacing human labor in

a. Hazardous environments,

b. Tedious jobs,

c. Inaccessible remote locations and

d. Unfriendly environments.

Automation possesses the following merits in our

technological society: reliability, reproducibility,

precision, independence of human fatigue and labor

laws, and reduced cost of high production (Valavanis,

Saridis 1992), with minimal human supervision,

leaving humans to perform higher level jobs.

Manufacturing on the other hand, dedicated to make or

process a finished product through a large scale

industrial operation. is an integral part of the industrial

process. In order to improve profitability, modern

manufacturing, which is still a disciplined art, involves

some kind of automation. Going all the way and fully

automating manufacturing is the dream of every

industrial engineer. However, as a work producing

process, it is generating Entropy producing

environmental pollution, loss of manual jobs, and

marketing.

The National Research Council reacted to these

problems by proposing among other items a new

discipline called: Intelligent Manufacturing (The

Comprehensive Edge 1989).

Intelligent Manufacturing is the process that utilizes

Intelligent Control, with entropy as a measure, in order

to accomplish reduction of entropy. It possesses

several degrees of autonomy, by demonstrating

(machine) intelligence to make crucial decisions

during the process. Such decisions involve scheduling,

prioritization, machine selection, product flow

optimization, etc., in order to expedite production and

improve profitability and creating non-recyclable

products which contain entropy. A case study of

Intelligent Manufacturing dealing with a nuclear plant

may be found in (Valavanis, Saridis 1992).

At the present time the application of such technology,

even though cost-effective in competitive

manufacturing, is faced with significant barriers due to

(The Comprehensive Edge 1989);

a. Inflexible organizations

b. Inadequate available technology

c. Lack of appreciation and

d. Inappropriate performance measures

However, globalization and international competition,

and the need for more reliable precisely reproducible

products is directing modern manufacturing towards

more sophistication with the generation of more

irreversible energy.

Automated multiple product scheduling is needed

when the factory produces more than one product on

the same set of stations and the ordering of production

must be set as a minimum operating cost scheduling

problem. The problem is mathematically formulated to

set the order of production using entropy as a measure

in the Intelligent Control’s three level structure

(Varvatsoulakis, Saridis, and Paraskevopoulos 1999).

The complete system is able to issue high-level task

plans and use them to control the stations of the

factory in the lower level of the hierarchy. The system

includes a learning algorithm designed to obtain

asymptotically optimal task plans for production

control in uncertain environments.
6.9 Socio-economic and Political Systems,

Globalization

Our societies have developed econometric (analytic)

systems to measure the conditions of the economy. A

typical document is the book by Faber, Niemes and

Stephan (1995) that gives analytic examples of the

various economic behaviors of markets using entropy

as a measure. This approach indicates the

accumulation of entropy that leads to disastrous global

equalization of the economy.

The modern attitude of global equalization of human

resources named globalization converges to an

equilibrium point of maximum entropy, where no

further progress in our planet is possible. All the

nations will have the same future without any chance

for growth or societal improvement. There are certain

advantages in globalization, like equally sharing the

wealth the food and the technological achievements of

the world. However, total equalization will lead to a

lack of progress and global boredom as a result of the

accumulated entropy, to say the least.

Governmental corruption, favoritism, and the resulting

absolutist behavior create a devastating worldwide

situation. Tastelessness in the Arts and Mass Media,

Globalization, and Politicalisation are main

characteristics.

A characteristic phenomenon of increase of global

entropy, similar to the effects of globalization, is the so

called “theory of anarchy” and its followers. Their no

order theories lead to a disastrous situation of global

maximum entropy and the methods used to implement

it are catastrophic. In theory these situations represent

a total equalization of the world that gradually

increases its entropy content.

In modern political ideology many systems are

decaying tending to a common denominator. An

example is “anarchy” which symbolizes the absolute

equality and resembles the entopic thermal death.

6.10 The Sciences and the Universe.

Phenomena in Modern Physics are prominent. Is

nuclear energy reversing the Entropy phenomena?

It may represent the energy of deterioration of spatial

bodies, or the death of stars according to “The “Big

Bang” theory.

The idea of irreversibility as the objective uncertainty

of a-priori solution was introduced in the designer’s

problem; it was reintroduced when considering that

control produces useful work on a system, which

generates the cost of performance as entropy (Saridis

1985). This irreversibility is interpreted by considering

that, when the cost of performance is paid, the system

cannot be recovered. This property can be witnessed

by visiting the junkyards of old automobiles: new cost

must be paid to recover the metal of the old wrecks or

in the construction of Space Stations, where the energy

of space transportation cannot be recovered.

7. SHOULD WE BE AFRAID OF ”CHAOS”

Entropy, as a philosophical device, gives a very

pessimistic outlook for the future of our world. It

represents energy and should be considered as such.

Thermal death in all its aspects, including total

equalization of our society, ecology, economy and

technology, tastelessness in art, and global boredom

are its characteristic predictions that the arrow of time

points at.

Should there be a possible cure of the problem? Is

death the end of the line? Should we hope that that a

supernatural deity will give continuity to the live of

our universe? Even though the arrow of time points

forward, the theory of chaos provides new situations,

which gives hope for alternatives than the thermal

death and the end of the world.

Life has always been based on a differential among its

elements and it is necessary for its existence. Chaos,

which considers points away from the equilibrium,

represents changes in behavior and therefore a

differential in activities. Therefore, it is a device

against the equilibrium and the thermal death. It gives

hopes for survival.

A typical example is Darwin’s theory of evolution of

the species (Brooks and Wiley, 1988), where

biological bifurcation of the genetic chains may serve

as a case of the theory of Chaos. Another example is

the perpetual energy emanating from the sun due to

nuclear reactions. They both represent the defeat of

thermal death and a hope for the continuity of the

future of our world.

Is there a conflict of the concept of entropy with God?

I do not believe so since it provides alternate solutions

that we witness in life. Chaos expresses an optimistic

answer to this question.

8. CONCLUSIONS

The concept of Entropy creates a pessimistic view for

the future of our universe. The equalization of all kinds

of sources of activities is leading to the equivalent of
thermal death and universal boredom of our world.

This, according to modern thoughts (Prigogine 1996),

may be due that sciences were recently considering

world phenomena only close to the equilibrium. An

excursion away from it, which has been developed

currently (Saridis 1995) promises changes of this

image. The theory of Chaos creates some hopes to

reverse the catastrophe. The possibility of colonization

of other planets may be the needed answer. The first

steps in that direction have already been taken.

9. REFERENCES

L Boltzmann, (1872) “Further Studies on Thermal

Equilibrium between Gas Molecules” Wien Ber., 66, p.

275.

W. L. Brogan, (1974) Modern Control Theory

Quantum Publishers New York N.Y.

D. R. Brooks and E. O. Wiley, (1988) Evolution as

Entropy University of Chicago Press, Chicago Il.

P. Coveney, and R. Highfield, (1990) The Arrow of

Time, Fawcett Colombine New York N.Y.

M. Faber, H. Niemes, G. Stephan, (1995), Entropy,

Environment and Resources Springer Verlag, Berlin

Germany.

Jaynes, (1957) "Information Theory and Statistical

Mechanics", Phys. Review, Vol. 4, p.106.

Ilya Prigogine,(1980), From Being to Becoming ,

Freeman and Company, San Francisco.

Ilya Prigogine,(1996), La Fin des Certitudes Editions

Odile Jacob, Paris France.

Jeremy Rifkin (1989) Entropy into the Greenhouse

World Bantam Books New York.

G. N. Saridis, (1995) Stochastic Processeses,

Simulation, and Control the Entropy Approach,

John Wiley and Sons, ew York.

Saridis, G. N., (1996), “Architectures for Intelligent

Controls” Chapter 6, in Intelligent Control Systems,

M. M. Gupta, N. K. Singh (eds) IEEE Press New

York NY.

G. N. Saridis (2001) Entropy in Control Engineering,

World Scientific Publishing Co. Singapore.

G. N. Saridis (2001) Hierarchical Intelligent

Machines, World Scientific Publishing Co.

Singapore.

Claude Shannon, W. Weaver (1963) The

Mathematical Theory of Communications, Aeolian

Books, Urbana Ill.

Madan G. Singh, (editor), (1987) Systems and Control

Encyclopaedia; Theory, Technology, Applications,

Vol. 1-8, Pergamon Press, Oxford UK.

Varvatsoulakis M., Saridis G. N., and

Paraskevopoulos P., (1998) “A Model for the

Organization Level of Intelligent Machines”

Proceedings of 1998 International Conference on

Robotics and Automation, Leuven Belgium May 15.

The Comprehensive Edge: Research Priorities for

U.S. Manufacturing (1989) Report of the National

Research Council on U.S. Manufacturing, National

Academy Press.
ISSUES IN STOCHASTIC TOCHASTIC SEARC

AND OPTIMIZATION PTIMIZATION

PerMIS 2004

NIST

James C. Spall

The Johns Hopkins University

Applied Physics Laboratory (JHU/APL)

james.spall@jhuapl.edu
Performance Metrics and Optimiz

Performance Metrics and Optimiz

• How are performance metrics used?

– Sensitivity studies– System design– Decision aid for strategic planning– Adapting system over time– Detecting instability; avoiding unstable performa– Evaluating system reliability– Design of experiments– Mathematical modeling and parameter estimatio– And on and on....

• Most of above involve optimization• Claim: Impossible to have a performance metri

conference w/o seriously considering optimiza
Search and Optimization Algorithm

Search and Optimization Algorithm

Part of Problem Solving Part of Problem Solving

• There exist many deterministic and stochastic alg• Algorithms are part of the broader solution

• Need clear understanding of problem structure, c

data characteristics, political and social context, li

algorithms, etc.

• “Imagine how much money could be saved if truly 

appropriate techniques were applied that go beyolinear programming.” (Z. Michalewicz and D. Foge

– Deeper understanding required to provide truly a

solutions; COTS usually not enough!

• Many (most?) real-world implementations involve 

effects
Potpourri of Problems Using Stoch

Potpourri of Problems Using Stoch

Search and Optimization Search and Optimization 

• Minimize the costs of shipping from production 

warehouses

• Maximize the probability of detecting an incomin

(vs. decoy) in a missile defense system

• Place sensors in manner to maximize useful inf• Determine the times to administer a sequence o

maximum therapeutic effect

• Find the best red-yellow-green signal timings in 

traffic network

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to serve an organization’s overall interests
Two Fundamental Problems of Int

Two Fundamental Problems of Int

• Let 

Θ be the domain of allowable values for a vec

•

θ represents a vector of “adjustables”

–

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Problem 1. Problem 1. Find the value(s) of a vector 

θ ∈ Θ

that minimize a scalar-valued loss function L

(

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Problem 2. Problem 2. Find the value(s) of 

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equation 

g

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g

(

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Continuous Discrete/

Continuous

Dis

Three Common Types of Loss Fun

Three Common Types of Loss Fun
Stochastic Search and Optimizat

Stochastic Search and Optimizat

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A. Random noise in input information (e.g., n

A. Random noise in input information (e.g., n

measurements of measurements of 

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— and/or

—

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B. Injected randomness (Monte Carlo) in cho

algorithm iteration magnitude/direction algorithm iteration magnitude/direction

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L

(

θ) (and its g

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• Injected randomness (B) in search magnitude/dir

offer benefits in efficiency and robustness

– E.g., Capabilities for global (vs. local) optimization
Some Popular Stochastic Search 

Some Popular Stochastic Search 

Optimization Techniques Optimization Techniques

• Random search• Stochastic approximation

– Robbins-Monro and Kiefer-Wolfowitz– SPSA– NN backpropagation– Infinitesimal perturbation analysis– Recursive least squares– Many others

• Simulated annealing• Genetic algorithms• Evolutionary programs and strategies• Reinforcement learning• Markov chain Monte Carlo (MCMC)• Etc.
Effects of Noise on Simple Optimization 

Effects of Noise on Simple Optimization 
Example Search Path (2 variables): St

Example Search Path (2 variables): St

Descent with Noisy and Noise Descent with Noisy and Noise

-Free 

Free 
• Consider tracking problem where controller and/

depend on design parameters 

θ

– E.g.: Missile guidance, robot arm manipulation, at

macroeconomic target values, etc.

• Aim is to pick 

θ to minimize mean-squared error 

• In general nonlinear and/or non-Gaussian system

possible to compute 

L

(

θ

)

• Get observed observed squared error by runn• Note that

– Values of 

y(

θ), not 

L

(

θ), used in optimization of 

θ

Example of Noisy Loss Measurem

Example of Noisy Loss Measurem

Tracking Problem Tracking Problem

θ = − (

L E ( ) actual output desired output

θ

≡ ⋅ 2

y( )

θ θ = =+ ⋅ 2 y L ( ) ( ) noise
• Have credible Monte Carlo simulation of real sys• Parameters 

θ in simulation have physical meanin

– E.g.: 

θ is machine locations in plant layout, timing 

traffic control, resource allocation in military opera

• Run simulation to determine best θ for use in rea

• Want to minimize average measure of performa

– Let 

y(

θ) represent one simulation output (

y(

θ) = 

L

(

Example of Noisy Loss Measurem

Example of Noisy Loss Measurem

Simulation Simulation

-Based Optimizatio

Based Optimizatio

Stochastic Stochastic optimizer optimizer Monte Carlo Monte Carlo 

y(

θ

)

Simulation Simulation

inputs
• Algorithm comparisons via number of evaluation

g

(

θ) (not iterations)

– Function evaluations typically represent major cos

• Curse of dimensionality

– E.g.: If dim(

θ) = 10, each element of 

θ can take on 

Take 10,000 random samples: Prob(finding one o

= 0.0005

– Above example would be even much harder with 

function measurements

• Constraints• Limits of numerical comparisons

– Avoid broad claims based on numerical studies– Best to combine theory and numerical analysis

Some Key Properties in Implementat

Some Key Properties in Implementat

Evaluation of Stochastic Algorith

Evaluation of Stochastic Algorith
Global vs. Local Solutions Global vs. Local Solutions 

• Global methods tend to have following characteri

– Inefficient, especially for high-dimensional

θ

– Relatively difficult to use (e.g., require very careful 

algorithm coefficients)

– Shaky theoretical foundation for global convergenc

• Much “hype” with many methods (genetic algorith

software advertisements):

– “...can handle the most complex problems, in

“...can handle the most complex problems, in

problems unsolvable by any other method.” problems unsolvable by any other method.” 

– “...uses GAs to solve “...uses GAs to solve any optimization proble

optimization proble

• But there are some mathematically sound metho

– E.g., restricted settings restricted settings for GAs, simulated annea

SPSA
No Free Lunch Theorems No Free Lunch Theorems

• Wolpert and Macready (1997) establish several 

Lunch” (NFL) Theorems for optimization

• NFL Theorems apply to settings where parame

and set of loss function values are finite, discret

– Relevant for continuous 

θ problem when conside

computer implementation

– Results are valid for deterministic and stochastic 

• Number of optimization problems

—mappings fr

set of loss values

—is finite

• NFL Theorems state, in essence, that no one s

algorithm is “best” for all problems
No Free Lunch Theorems No Free Lunch Theorems

—Basic For

Basic For

• Suppose that

Nθ

= number of values of 

θ

NL

= number of values of loss function 

• Then

(

) = number of loss functions

N

NL

θ

• There is a finite (but possibly huge) number of l

functions

• Basic form of NFL considers average performan

loss functions
Illustration of No Free Lunch Theo

Illustration of No Free Lunch Theo

(Example 1.7 in (Example 1.7 in ISSO)

• Three values of 

θ, two outcomes for noise free 

– Eight possible mappings, hence eight optimizatio

• Mean loss across all problems is same regardle

entries 1 or 2 in table below represent two possoutcomes

θ

1

2

2

1

2

1

1

3

θ

1

1

2

1

1

2

2

2

θ

1

1

1

2

2

2

1

1

1

2

3

4

5

6

7

θ

Map
No Free Lunch Theorems (cont

No Free Lunch Theorems (cont

• NFL Theorems state, in essence:• In particular, if algorithm 1 performs better than a

over some set of problems, then algorithm 2 perfthan algorithm 1 on another set of problems

• NFL theorems say nothing about specific algorit

specific problems

Averaging (uniformly) over all possible problems (loss functions L), all algorithm

perform equally well

Overall relative efficiency of two algorithmcannot be inferred from a few sample pro
Relative Convergence Rates of Deter

Relative Convergence Rates of Deter

and Stochastic Optimization and Stochastic Optimization

• Theoretical analysis based on convergence rate

iterates where 

k is iteration counter

• Let 

θ

∗ represent optimal value of 

θ

• For deterministic deterministic optimization, a standard rate 

• Corresponding rate with noisy measurements noisy measurements• Stochastic rate inherently slower in theory and p

ˆ , θ

k

O

∗

ˆ

− = << ( ), 0 1 k θ θ k c c

O

∗

λ

⎛ ⎞ − = <≤ ⎜ ⎟ ⎝ ⎠

1

2

1

ˆ

k , 0

k

θθ λ
Concluding Remarks Concluding Remarks

• Stochastic search and optimization very widely us

– Handles noise in function evaluations– Generally better for global optimization– Broader applicability to “non-nice” problems (robus

• Some challenges in practical problems

– Noise dramatically affects convergence– Distinguishing global from local minima not genera– Curse of dimensionality– Choosing algorithm “tuning coefficients”

• Rarely sufficient to use theory for standard determ

methods to characterize stochastic methods 

• “No free lunch” theorems are barrier to exaggerat

power and efficiency of any specific algorithm 

• Algorithms should be implemented in context: “B

rough answer to the right question than an exto the wrong one” (Lord Kelvin)
Selected References on Stochastic Opt

Selected References on Stochastic Opt

• Fogel, D. B. (2000), Evolutionary Computation: Toward a New 

Machine Intelligence (2nd ed.), IEEE Press, Piscataway, NJ.

• Fu, M. C. (2002), “Optimization for Simulation: Theory vs. Practice” 

by S. Andradóttir, P. Glynn, and J. P. Kelly), INFORMS Journal on 14, pp. 192

−227.

• Goldberg, D. E. (1989), Genetic Algorithms in Search, Optimizatio

Learning, Addison-Wesley, Reading, MA.

• Gosavi, A. (2003), Simulation-Based Optimization: Paramet

Techniques and Reinforcement Learning, Kluwer, Boston. 

• Holland, J. H. (1975), Adaptation in Natural and Artificial System

Michigan Press, Ann Arbor, MI. 

• Kushner, H. J. and Yin, G. G. (2003), Stochastic Approximation 

Algorithms and Applications (2nd ed.), Springer-Verlag, New York.

• Michalewicz, Z. and Fogel, D. B. (2000), How to Solve It: Mo

Springer-Verlag, New York. 

• Spall, J. C. (2003), Introduction to Stochastic Search and Optimiza

Simulation, and Control, Wiley, Hoboken, NJ.

• Zhigljavsky, A. A. (1991), Theory of Global Random Search, K

Boston. 
Contact Info. and Related Web S

Contact Info. and Related Web S

• james.spall@jhuapl.edu• www.jhuapl.edu/SPSA (Web site on stocha

approximation algorithm)

• www.jhuapl.edu/ISSO (Web site on book 

Introduction to Stochastic Search and Optim
Comparing Algorithms: Rules of Thumb and an Example

S. Balakirsky, T. R. Kramer

National Institute of Standards and Technology

Gaithersburg, MD 20899

ABSTRACT

This paper provides twenty rules of thumb for comparing

algorithms having the same function, one of which is to be

selected for use in an intelligent system. The rules are

illuminated by a specific example, the comparison of three

algorithms for dealing with the collection of open nodes that is

at the heart of the Dijkstra graph search method. For each rule,

a description is given of how the rule was applied in building

the example.

KEYWORDS: algorithm, binary tree, compare, Dijkstra,

graph, jump search, list, run time, search

1. INTRODUCTION

To produce intelligent behavior, most intelligent systems

include computer implementations of one or more complex

algorithms. Often a comparison must be done to support

making a choice among algorithms performing the same

function.

This paper1 provides a set of rules of thumb for comparing

algorithms having the same function. The rules given here are

elementary. Most readers will already know many or all of

them. The paper also presents a specific example of comparing

algorithms. The example is intended to highlight the utility of

following the rules. Our purposes are to help builders of

intelligent systems make better decisions among competing

algorithms and to encourage caution and thoroughness in

comparing algorithms.

Section 2 gives our rules of thumb for comparing

algorithms for use in an intelligent system. Section 3 presents

the example, comparing algorithms for dealing with open

nodes in Dijkstra graph search. Section 4 discusses how the

rules were used in the example. Section 5 gives the paper’s

conclusion.

2. RULES OF THUMB

RULE OF THUMB 1: Compare algorithms both in theory

and in practice. Algorithms may be compared using theory (by

examining how they work) or using experimentation (by

examining the behavior of a system running an implementation

of the algorithm). Both methods should be used. Theory directs

experimentation, but reality is sufficiently more complex than

theory that it is naive to rely on theory alone.

2.1 Comparing Algorithms in Theory

RULE OF THUMB 2: Do a big O analysis. Theoretical

analysis of the running time of algorithms is a mainstream

activity of computer science. The well-known idea [7], [11] is

to identify the “big O” order of the time a program will take as

a function of the size of the problem being solved. The

difficulty of doing this ranges from fairly easy to impossible. A

theoretical analysis can never guarantee an algorithm will work

well, but if it indicates the algorithm should work badly for

large problems (by running in order 2N time, for example,

where N quantifies the size of the problem under

consideration), one can be quite sure it will work badly.

Depending on the application, it may be appropriate to do a

worst-case analysis, an average behavior analysis, or both.

If the order of time taken, T, is O(F(N)) for some function

F, this means, T = K(F(N)) for some constant K. The constant

of proportionality, K, is constant only for a given computer,

compiler, and operating system. If the usual assumption of a

one-tier memory model (only RAM) is made, K may still fail to

be constant. As pointed out in [8], modern computers generally

have a multi-level memory hierarchy, including at least cache,

RAM, and disk. Cache memory may be up to ten times as fast

as RAM, and disk memory may be 1000 times as slow. Thus, K

will actually be a constant only if the characteristics of memory

handling do not change over the range of N being tested.

RULE OF THUMB 3: Do a functional analysis. A

functional analysis is an analysis of how the algorithm works

— what the main routine does, what the subroutines are and

what they do, etc. This is a harder, one-off activity, usually

requiring understanding of a large body of source code or

pseudocode and the language in which it is written. Here again,

only negative guarantees are available; if it does not work in

theory, it won’t work in practice.

RULE OF THUMB 4: Identify dimensions of the

domain space. Typically, the problem domain an algorithm

addresses will have several independent aspects that affect the

functioning of the algorithm. These aspects can be used as the

dimensions of a domain space. Some aspects, such as problem

size, may be effectively continuous, while others may have

continuous segments divided by discontinuities or may be

discrete.

RULE OF THUMB 5: Identify regions of interest in the

domain space. Also typically, only a limited part of a domain

space will be of interest. The portion of interest may be

1. Certain commercial equipment, instruments, or materials are

identified in this paper in order to facilitate understanding. Such

identification does not imply recommendation or endorsement

by the National Institute of Standards and Technology, nor does

it imply that the materials or equipment identified are

necessarily the best available for the purpose.
bounded either naturally (by discontinuities in the dimensions

of the space), or synthetically (by picking limits along

continuous dimensions). It is important to identify the regions

of interest because algorithms may, and almost always do,

perform qualitatively differently in different parts of the space.

In this paper, we use the term “sea change” to mean a

qualitative change in the functioning of an algorithm in

different parts of the domain space.

RULE OF THUMB 6: In the functional analysis,

consider all regions of interest in the domain space. A

functional analysis will not be complete unless it identifies (i)

what is qualitatively different in different parts of the domain

space where the algorithm is intended to work, and (ii) how

qualitative differences in the part of the domain space affect the

performance of the algorithm.

RULE OF THUMB 7: Get the source code. While natural

language and pseudocode versions of algorithms can be

analyzed, the analysis is likely to miss key points if it is not

done on the source code, the first key point being: does the

code implement the algorithm correctly. Without having the

code in hand, it cannot be debugged, modified, or recompiled.

2.2 Comparing Algorithms in Practice

Where theoretical analysis is not well-developed, only

experimentation is available to compare algorithms. Even

where a theoretical analysis of algorithm performance is

available, it cannot reveal how an implementation will perform.

An abstract algorithm does not run on an abstract machine. An

implementation of the algorithm in a specific computer

language, compiled by a specific compiler (or interpreted by a

specific interpreter) for a specific machine architecture is what

runs. And it runs on a specific piece of computer hardware,

under control of a specific operating system, possibly

depending on a specific file server connected by a specific

communications system. Each of these items can affect the

performance of an algorithm [6], [8].

RULE OF THUMB 8: Determine what is to be

optimized, and test that. This is obvious but ranges from easy

to nearly impossible in practice. Algorithms that return an

answer guaranteed to be optimal for a well-defined single

measure (least cost, for example) provide the easy cases. In

hard cases (computer vision has them), it is difficult even to

characterize what one is trying to optimize. There may be

trade-offs among optimizing several aspects of performance:

average performance vs. worst-case performance, minimizing

bad results vs. maximizing good ones, minimizing running

time vs. maximizing answer quality, falling off a cliff at

domain region boundaries vs. sliding down gradually, etc.

RULE OF THUMB 9: In experiments, keep the number

of variable factors to a minimum. This is a main tenet of

standard experimental procedure, which should be followed

insofar as possible. Keep all conditions but one the same

between tests, changing only one factor at a time. In particular,

when comparing two algorithms, to the extent possible:

1. Implement them in the same computer language.

2. Compile them on the same compiler, using the same

compiler settings.

3. Run them on the same computer.

4. Test them under similar conditions of computer usage.

If it is known what computer the algorithm will be running

on as part of the complete intelligent system, that is the

computer that should be used for testing. Otherwise, the same

tests should be repeated on each computer that might be used

in the full system.

RULE OF THUMB 10: Conduct one or more series of

tests that are ordered by size but have the same values in

other dimensions. If problem size is variable in an application,

it usually varies continuously. The range of sizes should match

the range presented by the regions of interest in the domain

space, if that is known. When such a series of tests is

conducted, if theory indicates there are no sea changes in

system behavior across the range of sizes, test results (such as

time) should lie on a smooth curve of some sort when the

results are plotted on a graph showing problem size on one axis

and results on the other axis. If there is a kink in the curve

where theory does not predict a sea change, double-check the

theoretical analysis and/or run the same tests on a different

computer. If the kink is not found on a second computer, the

cause of the kink lies somewhere in the first computer.

RULE OF THUMB 11: Conduct identical tests on

substantially different computers. If the same tests can be run

on substantially different computers, and the ratio of the times

taken by the two computers is nearly constant across tests, this

is (mushy) evidence that the system operating regimes are not

undergoing sea changes between tests. If one of the computers

behaves qualitatively differently between two tests, it is

unlikely that the second computer will have a sea change at the

same point.

RULE OF THUMB 12: Conduct tests with the computer

lightly loaded. The two most significant measures of load on

the computer are memory usage and CPU usage.

If RAM memory is not lightly loaded, the operating

system will use secondary memory with the effect, according

to [8], that “memory access times can vary by factors as large

as a million” in the worst case. The same paper observes that

because of memory effects, “[predicted] running times that are

off by three orders of magnitude are not unusual.”

Reduce the number of processes competing for time as far

as possible while testing. For example, do not run two tests

simultaneously. Ideally, while many processes will inevitably

be resident on the test computer, only the process being tested

should use any significant amount of CPU time. The Unix

“time” command, for example, shows the percentage of CPU

time used by the process that was timed. If this command is

used for timing, use results only for those runs for which CPU

usage is near 100%.

RULE OF THUMB 13: Monitor computer use during

testing. Memory usage per process on Sun computers1 and

other computers using unix-like operating systems may be

checked with top or ps. Top also shows total memory usage.

1. In this paper, “Sun computer” means a Sun computer running

the Solaris operating system (which is unix-like).
Memory usage per process and in total on PC’s1 may be

checked using the Windows Task Manager.

CPU usage for a process may be checked on computers

using unix-like operating systems with the top and time

commands. Top also shows total CPU usage. On PC’s, a

performance meter is available inside the Windows Task

Manager (and in a stand-alone process) that will show total

CPU usage. On PC’s the Windows Task Manager will show

CPU usage per process.

Monitoring processes are designed to use minimal

computer resources, so having them running while testing will

probably not interfere with testing. Some monitoring processes

(top, for example) show what resources they themselves are

using. If it is suspected that a monitoring process is using

significant resources, run a timing test with the monitor on,

then run the same test with the monitor off and compare results.

RULE OF THUMB 14: Conduct tests with the computer

realistically loaded. Conducting tests with the computer lightly

loaded should always be done, but a light load may not be

possible in the full system. If the load on a computer running

the full system is known, conduct tests under those load

conditions. Where performance changes dramatically between

lightly loaded and realistically loaded conditions, consider

reconfiguring the full system.

RULE OF THUMB 15: Understand the effects of the test

harness and compensate for them. The algorithm being tested

will have interfaces to the rest of the full system and may

require data structures to exist. To test without the full system,

a test harness is built, typically in the form of computer code

for a driver including a main routine and routines to set up data.

If the full system normally builds data structures while it runs,

as opposed to building them by reading a file, it may be

necessary to define a file format and have file-reading code in

the driver. When tests are run using the harness, some time will

be used by the driver code. If time to do the same functions is

not required by the full system, that time should be diluted or

subtracted in analyzing test results.

Typically, a test harness will consume a significant amount

of time primarily when it starts up (for file reading, for

example), and possibly when it shuts down.

RULE OF THUMB 16: Use representative test cases.

The test cases used should be typical of the region of domain

space for which an algorithm is being tested. If possible,

harvest test cases from data acquired during intelligent system

operation. It is very rare for a test case generator to exist that is

guaranteed to produce test cases that satisfy some metric for

representativeness. Producing representative test cases

typically requires both establishing criteria for

representativeness and conducting secondary experiments on

candidate test cases to see how well they meet the criteria.

RULE OF THUMB 17: Use standard test case sets, if

available and appropriate. In some domains, standard sets of

test cases may be available. Even where these are available, care

is needed in deciding if they are really in the proper domain

region and, if so, whether they are adequately representative.

A common pitfall with test cases is that an algorithm is

tuned for a specific set of test cases that are not adequately

representative of the domain region. When further testing is

done or the full system is built and run, performance is

significantly lower than expected. Where no good metric for

representativeness exists, the only solution for this problem

may be to use very large sets of test cases.

RULE OF THUMB 18: Collect secondary data showing

what the algorithm is doing internally. This is useful for:

1. verifying that data which should be the same between

two algorithms or implementations is the same.

2. verifying that an algorithm is doing in practice what

it should be doing in theory.

3. tuning the algorithm for better performance.

4. understanding where the algorithm is spending the

majority of its time.

This is at the border between testing and debugging. If an

algorithm is not doing what the tester thinks it should be doing,

either the tester is confused or there is a bug in the code or the

algorithm itself.

RULE OF THUMB 19: Deal with measurement error.

Another obvious rule. This is like “check the hull for leaks” in

that checking any one spot is easy, but there may be a lot to

check, and if you miss one spot, the boat sinks. Deciding

between algorithms does not usually require high precision or

high accuracy; getting measurements within 10% to 20%

overall is probably good enough. Where components of error

are additive, of course, the error in an individual component

needs to be lower.

Quick checks should be applied to measuring tools such as

the time or top command or a performance monitor. Things

that measure time can be double-checked against clocks or

watches. Where more than one tool is available, use both and

compare. For example, CPU usage on a Sun computer is given

both by time and top.

Much of the data taken by computer tools such as top and

performance monitors is an average over some time period,

and one should be aware of this when using those tools. For

example, performance monitor plots may show CPU usage

ramping up over a few seconds, staying level for a long time,

and then ramping down again. The ramps are almost certainly

not real. What is actually happening is a quick jump from low

to high when a process starts and a jump back to low when the

process ends. The ramps (which help the eye follow the curve)

are artifacts of using a rolling time average. The real life span

of the process is probably from the beginning of the ramp up to

the beginning of the ramp down.

Performing repeatability tests is very useful. The total

variation in a repeated test contains at least three components,

each of which has random and systematic parts:

1. variation caused by differences in the internal

computer environment between tests.

2. errors in the tools used to take the measurements.

3. errors in reading the measurements provided by the

tools.

Although equal and opposite random errors are possible in

theory, they are unlikely to occur repeatedly in practice. If the

variation between repeated measurements is small in every

1. In this paper, “PC” means a PC running an MS Windows

operating system.
case, it is nearly certain that all three components of random

error are small. If possible, adjust test procedures so that

variations in repeated tests are small compared with the

quantity being measured.

RULE OF THUMB 20: At widely separated times, repeat

tests performed earlier. Repeating old tests will help catch

systematic errors that vary slowly over time.

3. Example

Many systems may use a graph search algorithm. In building

planning systems for domains as diverse as autonomous

vehicles [3] and automated atom assembly, researchers at NIST

have been using Dijkstra graph search [5]. This finds a least

cost path (if there is any path) between any two nodes in a

directed graph. In previously reported work [4], we compared

three implementations of the Dijkstra algorithm. We were

aware that even the best of these three (which we will call List)

could be improved by implementing faster methods of using

the collection of open nodes that is at the heart of Dijkstra

graph search. List maintains the open nodes in a linked list

arranged in increasing cost order. List uses linear search for

removing and reinserting nodes whose cost changes. We

implemented two algorithms embodying more efficient

methods of dealing with the open nodes. The first of these also

keeps the open nodes in a list but is a form of jump search [10]

that overlays the list with more structure; the system that uses it

we call Tabs. The second uses a type of binary tree for the

open nodes [1], [2], [12], and the system using it we call AVL.

We ran a series of tests on List, Tabs, and AVL and compared

them. This paper uses that comparison as an example. Test data

and descriptions of the tests are given here. Details of the

algorithms are given in a separate, not yet published paper.

The three implementations all produce the same results in

theory, and the results are guaranteed to be optimal (measured

by least cost). Theoretical analyses of average time for removal

and insertion operations on the collection of open nodes are

straightforward. They show average times of O(M) for List,

O(sqrt(M)) for Tabs, and O(log(M)) for AVL, where M is the

size of the open nodes collection. As discussed in [9], however,

the theoretical average time of graph search is generally

computable (with difficulty if at all) only for well-characterized

graphs over which the average is to be taken. In order to apply

the average time equations just given, we need to know how M

varies during operation, on the average, for a given number of

nodes N, and this depends heavily on the characteristics of the

test graphs. The test graphs we used are well-characterized as

follows, but we do not have average time equations for nodeto-node searches in graphs with these characteristics.

The sets of test graphs have the following characteristics:

1. In each set, each graph has twice as many nodes as

the preceding graph.

2. In each set, the number of arcs leaving a node is

fixed; one set has 16 arcs from each node, the other 2

arcs from each node.

3. The cost of each arc is a randomly chosen positive

integer less than 50.

4. The node at the end of the each arc is randomly

chosen, except that the node at the end must differ

from the node at the beginning, and for a given

beginning node, the end nodes must all differ.

5. Each graph is not necessarily completely connected.

Although we do not have big O equations for expected

behavior, we knew from our functional analysis of the

algorithm that nearly all of the processing time is spent in

removing nodes from the open nodes collection and inserting

nodes back into this collection. It was also clear that the average

M gets bigger as N gets bigger. Thus, since M/sqrt(M) and M/

log(M) increase rapidly with M, we expected Tabs and AVL to

outperform List by increasing margins as N increases. Since

sqrt(M)/log(M) increases as M increases, we also expected

that for sufficiently large N, AVL would be faster than Tabs.

We ran tests first on a Sun Ultra 60 and then on a Pentium

4 class PC. Both computers have 512 megabytes of RAM

memory. The PC is at least 5 years newer, so we expected it

both to run faster and to do more active memory management.

The results for the Sun are shown for branching factor 16

in Figure 1, and for branching factor 2 in Figure 2. Rather than

showing times for the three algorithms, the graphs show the

ratio of the time taken by List to the time taken by AVL and

the ratio of the time taken by List to the time taken by Tabs.

The basic reason for using the ratio is because we are

comparing algorithms, and using the ratio washes out the

effects of using a specific problem, leaving only the effects of

the algorithms. Further discussion is given in Section 4.

As shown in the figures, our expectations were correct.

AVL and Tabs both outperform List by increasing margins as

N increases and AVL outperforms Tabs by an increasing

margin when N is more than 8000. Smooth curves fit the data

very closely, implying that for both sets of test cases, there was

no sea change in the behavior of the Sun over the range of

graph sizes we used.

Figure 3 shows a comparison of speed on the sun versus

speed on the PC. Since the same source code was used on the

Sun and the PC, we expected that, in the absence of a sea

change in behavior of the PC at some point, the speed ratios

would be roughly constant over the range of problem sizes and

that the ratio would be about the same for all three systems.

Figure 3 shows that this was the case for AVL and Tabs, but

not for List. Further discussion is given in Section 4.

From the functional analyses of the three systems, we

expected the search time taken by each implementation to be

almost proportional to the number of comparisons performed.

This is because, except for the main loop, most of the code

consists of loops or recursive function calls in which the

number of repetitions depends on a comparison, and the other

operations that execute during a repetition are always the same

for the code segment performing the repetition. List has the

fewest other operations per comparison, while AVL has the

most, so we expect comparisons per second to decrease from

List to Tabs to AVL. As shown in Table 1 below, the data for

branching factor 16 largely bear this out. For each of the three

systems and four test cases, the table shows the time taken on

the Sun computer to find the answer and the number of

comparisons made while finding the answer. The times taken

on the PC differed, but the numbers of comparisons did not.
2-1 25 26 27 21 20 23 24 22

21

22

23

24

25

26

27

Thousands of Nodes

Relative Speed

Figure 1. Speed Relative to List

for Branching Factor 16, Sun

28

KEY

AVL

Tabs

29

2-1 25 26 27 21 20 23 24 22

21

22

23

24

25

26

27

Thousands of Nodes

Relative Speed

Figure 2. Speed Relative to List

for Branching Factor 2, Sun Computer

28

KEY

AVL

Tabs

Table 1: Data for Branching Factor 16, Sun

type↓ nodes

→

1000 4000 16000 64000

AVL seconds 0.0111 0.0605 0.268 1.64

comps 20,167 108,812 458,585 2,392,759

Tabs seconds 0.00836 0.0515 0.334 4.56

comps 34,841 247,648 1,899,736 22,214,824

List seconds 0.0694 1.31 22.7 693

comps 523,530 9,338,357 130,440,329 2,417,260,900

2-1 25 26 27 21 20 23 24 22

1

2

3

4

5

6

7

Thousands of Nodes

Relative Speed

Figure 3. Speed on PC Relative to

Speed on Sun, for Branching Factor 16

8

KEY

AVL

Tabs

List
4. How the Example Used the Rules

RULE OF THUMB 1: Compare algorithms both in theory

and in practice. This was done, as described in Section 3.

RULE OF THUMB 2: Do a big O analysis. This was

attempted as described in Section 3.

RULE OF THUMB 3: Do a functional analysis. We

studied the functioning of the algorithms for handling the

collection of open nodes. The functional analysis did not reveal

any characteristics of the algorithms that would be expected to

produce sea changes in the regions of graph space of interest.

RULE OF THUMB 4: Identify dimensions of the

domain space. We were not focused on a specific application

for this work, so we looked at the characteristics of abstract

directed graphs (what the Dijkstra algorithm deals with).

Following Rule of Thumb 10, we used problem size as one

dimension.

In our earlier paper, [4] on testing implementations of the

Dijkstra algorithm, the functional analysis indicated that

versions that keep the list of open nodes in cost order will

differ from versions that do not keep the list in order. This

difference appeared when the branching factor of the graph

(how many arcs leave each node) was used as a dimension of

the domain space. We continued to use the branching factor as

a dimension in the tests reported in this paper, even though we

did not expect to see significantly different behavior on this

dimension.

RULE OF THUMB 5: Identify regions of interest in the

domain space. In automated atom assembly, we have dealt

with graphs having 62 to 437,582 nodes using Dijkstra search.

Other applications have not had as large an upper bound. The

limits of our testing were within a somewhat narrower range:

500 to 128,000 nodes.

RULE OF THUMB 6: In the functional analysis,

consider all regions of interest in the domain space. As

already described, the region of interest was in graph space and

was all one piece. It did not have qualitatively different parts.

RULE OF THUMB 7: Get the source code. This was

easy, since we wrote the code.

RULE OF THUMB 8: Determine what is to be

optimized, and test that. The Dijkstra algorithm does not halt

until an optimum (least cost) answer is found. We accepted

optimizing cost, as provided by the algorithm in its usual form.

Since there is no way to predict the cost of the answer before

the search is conducted, it is not possible to stop the search

when a 120% optimum cost (or whatever fraction or margin)

solution is found. The Dijkstra algorithm could readily be

modified either to stop at some point between finding the first

answer and finding an optimal answer or to keep going after

finding the first optimal answer until all equally optimal

answers have been found, but we did not do this.

RULE OF THUMB 9: In experiments, keep the number

of variable factors to a minimum. Our tests included three

variable factors: the computer (Sun or PC), branching factor of

the graph (2 or 16), and problem size (500 to 128,000 nodes).

In the range 1000 to 64,000 nodes, the 3-dimensional test space

has all data points lying on lines for which two of the three

variables are constant. For example, as shown in Figure 1, the

computer and the branching factor were held constant while

problem size was varied.

To reduce variable factors in the source code, we

remodularized the code. We placed the code defining a graph, a

node, and a Dijkstra search node in the file dijk.hh and used

this file in building each of the three systems. We built the test

harnesses for AVL and Tabs by copying the harness for List

and changing a very few lines.

RULE OF THUMB 10: Conduct one or more series of

tests that are ordered by size but have the same values in

other dimensions. Two series of tests in increasing size order

are shown in Figure 1 and Figure 2 for the Sun Computer. The

same tests were run on a PC and used for building Figure 3.

RULE OF THUMB 11: Conduct identical tests on

substantially different computers. We ran the same test cases

on both a Sun and a PC. These are known to be substantially

different.

Figure 3 shows that for Tabs and AVL, the ratio of the

speed of the PC to the speed of the Sun is almost constant over

the range of sizes tested for branching factor 16. Tabs runs

about 6.6 times as fast on the PC. AVL runs about 6.0 times as

fast on the PC. For List, the ratio is not constant, decreasing by

a factor of about 2 over the same range. This appears to

indicate a sea change in the behavior of the PC over this range.

Since we expected more active manipulation of memory on the

PC, but we determined that secondary memory is not being

used, we hypothesize that the sea change is caused by a

difference in the use of cache memory between the smaller and

larger problems. We have not tried to verify this.

If figures similar to Figure 1 and Figure 2 were drawn for

the PC, they would not have the nice appearance of those

figures because the algorithm comparison would be

confounded by the sea change in computer behavior. If we had

tested only on the PC, we would have had a very hard time

determining whether the algorithm or the computer was

responsible.

RULE OF THUMB 12: Conduct tests with the computer

lightly loaded. For both Sun and PC, we made sure no

processes were running that would compete significantly for

system resources. While any test was in progress we did not

move the mouse or touch the keyboard. The following

observations establish that both computers were always lightly

loaded during tests.

RULE OF THUMB 13: Monitor computer use during

testing. On the Sun, we monitored with both time and top that

the test process was using almost all of the CPU. When testing

on the Sun, we recorded results only when CPU usage was at

least 98% according to the results provided by the time

command.
On the PC we used the Task Manager and/or the

performance monitor to monitor CPU usage. In all cases, CPU

usage was at zero both before and after each test. During tests

run on the PC, CPU usage reached a very flat plateau at 50%,

as opposed to just under 100% on the Sun. This may indicate

that the PC operating system’s CPU allocation policy does not

allow any process to have more than half the CPU, even if the

other half is available. We did not attempt to investigate this

further.

The Sun and the PC each had 512 megabytes of RAM

memory. On the Sun, the largest any search process became

was 13 megabytes. There were always over 100 megabytes of

free RAM and no CPU time was spent on swapping. On the

PC, the largest any search process became was 22 megabytes.

There were always over 200 megabytes of free RAM and no

CPU time was spent on swapping.

We checked that none of the monitors uses a significant

portion of the CPU.

RULE OF THUMB 14: Conduct tests with the computer

realistically loaded. Our tests were not conducted using a

complete intelligent system. We did not know what a realistic

load would be, so we did not do this.

RULE OF THUMB 15: Understand the effects of the test

harness and compensate for them. The test harness for

Dijkstra search was a main routine taking four arguments (i)

the name of a graph file, (ii) the node number of the start node,

(iii) the node number of the goal node, (iv) the number of times

to repeat the search. The number of times to repeat the search

was selected so as to satisfy the requirement that the total time

taken by the test be at least 30 seconds. Preliminary testing of

each test case was done to determine a number of repetitions

that would meet this requirement but not need more than a few

minutes for each test.

A file format for an abstract directed graph was devised,

and a file reader was built into the test harness that would read

the file and build a directed graph structure. Testing revealed

that the smaller files were read in a second or less, but the

larger ones required up to 7 seconds on the Sun and up to 18

seconds (for the same file) on the PC. We did not attempt to

determine why the PC was slower. The reading time was

calculated by running the same test with two different numbers

of repetitions and using the equation TotalTime = (ReadTime +

(RunTime x repetitions)). The reading time was also observed

on the PC performance meter. Where reading times were more

than a second, the run times were calculated using the equation

just given.

Reading times are out of the scope of comparing the

algorithms we were comparing. They are effects of the test

harness, and we compensated for them.

The other effect of the test harness we identified was the

time taken by the “for” loop that repeats the test. Each time

around that loop, each node in the graph is marked

UNOPENED, since Dijkstra search requires that marking

when it starts up. This is a very small amount of processing

compared with the processing done on nodes in Dijkstra

search, so we did not compensate for it.

RULE OF THUMB 16: Use representative test cases.

The graphs we used were constructed (by a graph-building

program we wrote) to produce graphs with the characteristics

described earlier. The user of the program specifies number of

nodes, the branching factor, and an upper bound on arc cost. In

real problems, a constant branching factor seems unlikely. We

doubt that the algorithms would have compared differently if

we had used variable branching factors, but we have neither an

analysis nor experimental data to substantiate that. Since our

graph construction methods were not selected to produce

graphs similar to those found in any specific application, we

cannot claim that the test graphs are representative.

An equally severe problem was picking the start and goal

nodes for each test case. Clearly, in each graph we constructed,

some pairs of nodes would be connected by a short cheap path

while other pairs would be connected only by more expensive

longer paths. Finding the least expensive path would be

relatively easy for the short cheap paths and relatively hard for

the long expensive paths. To get average results, in each graph,

we could have randomly selected a set of pairs, repeated the

tests for all pairs in the set, and averaged the results. This

would have required a much larger amount of testing than we

were prepared to do. Instead, for each graph we randomly

selected a set of 7 pairs, timed all 7 pairs using AVL and only a

few repetitions to identify the pair with median time, and used

that one pair as the representative for the graph in testing with

List and Tabs and retesting with AVL.

This selection procedure still left substantial differences in

the relative difficulty of the test cases. When run time was

plotted against problem size for the algorithms being tested,

the resulting lines were rather jagged. But the three curves

zigged and zagged together, implying the zigs and zags were

effects of problem difficulty, not the algorithms being tested.

This suggested factoring out the difficulty of the representative

problem by plotting the ratios of the times, not the actual times,

and that is what we did.

For a specific instance of a test case, the time taken can be

viewed as the relative difficulty of the test case (compared with

the average difficulty) multiplied by the average time taken. If

the average time taken is given by T = F(N), then letting DCase

be the relative difficulty, the equations for time taken for a

specific test case are:

TListCase = DCase x FList(N),

TTabsCase = DCase x FTabs(N), and

TAVLCase = DCase x FAVL(N).

When the ratio of any two times is taken, the Dcase in the

numerator cancels with the Dcase in the denominator, removing

the effect of the difficulty of the case.

RULE OF THUMB 17: Use standard test case sets, if

available and appropriate. We are not aware of any standard

test case sets for pure graph search using the range of sizes and

branching factors we have used.
RULE OF THUMB 18: Collect secondary data showing

what the algorithm is doing internally. We collected

secondary data for three purposes: (i) to be sure List, AVL, and

Tabs were behaving identically where they were supposed to

be doing so, (ii) to determine how the Dijkstra algorithm

behaves on problems with different sizes and branching

factors, (iii) to measure those things that analysis indicated the

three algorithms would do differently.

We collected secondary data by adding conditionally

compiled code to the source code files for the three systems.

Timing tests were conducted with versions of the executable

systems compiled without data collection. A subset of the same

tests were repeated with versions of the systems compiled with

data collection.

To be sure the systems were behaving identically where

they should be identical, two files were generated: one listing

the node numbers in the order in which they were opened and

giving the total number of nodes opened, and the other listing

the total number of nodes open each time around the node

processing loop of the Dijkstra algorithm. For each test case,

files generated on the Sun by the three systems were compared

and the data items just mentioned were found to be identical.

For a few test cases, similar files were also generated on the

PC. All data that should be identical were found to be identical,

even the maximum 2,417,260,900 comparisons.

RULE OF THUMB 19: Deal with measurement error.

When testing on the PC, a digital watch reading in seconds was

used to time the tests. Since this automatically introduces a

random error of one second, all tests on the PC were adjusted

to run for at least 30 seconds, so that the random error from

reading the watch would not be more than about 3% of the time

being measured. Timing for the PC was spot-checked using the

PC’s performance monitor. Timing on the Sun was done with

the time command; spot checks were done with a digital watch

and an analog clock.

RULE OF THUMB 20: At widely separated times,

repeat tests performed earlier. This rule was followed

throughout testing. No significant increases in variability

occurred.

5. Conclusion

This paper has presented 20 rules of thumb to follow in

comparing algorithms performing the same function that might

be used in an intelligent system. An example was provided of

how the rules were applied in comparing three algorithms for

maintaining the collection of open nodes in Dijkstra search.

For some rules, the example described a pitfall that was

avoided by having followed the rule. For other rules, the

example showed how difficult it can be to follow the rules.

The rules of thumb presented here can certainly be improved,

and surely there are other rules it would be helpful to add. The

intent of these rules is to help builders of intelligent systems

make better decisions among competing algorithms. We hope

they will be useful for that purpose.

6. References

[1] Adelson-Velskii, G. M. and Landis, E.M., “An Algorithm

for the Organization of Information”, Doklady Akademiia

Nauk SSSR, Vol. 146, No. 2, 1962, pp. 263-266.

[2] Baeza-Yates, R., “Height Balance Distribution of Search

Trees”, Information Processing Letters, Vol. 39, No. 6, 1991,

pp. 317-324.

[3] Balakirsky, Stephen B., Lacaze, Alberto, “Value-Driven

Behavior Generation for an Autonomous Mobile Ground

Robot”, in Proceedings of the SPIE 16th Annual International

Symposium on Aerospace/Defense Sensing, Simulation and

Controls, Orlando, FL, April 1-5, 2002.

[4] Balakirsky, Stephen B., and Kramer, Thomas R., “NOT

(Faster Implementation ==> Better Algorithm), A Case

Study”, in Proceedings of the PerMIS ‘03 Workshop, NIST

Special Publication 1014, 2003.

[5] Dijkstra, E. W., “A note on two problems in connexion

with graphs,” Numerische Mathematik, Vol. 1, 1959, pp. 269-

271.

[6] Hooker, J. N., “Needed: An Empirical Science of

Algorithms”, Operations Research, Vol. 42, No. 2, MarchApril 1994, pp. 201-212.

[7] Knuth, Donald E., The Art of Computer Programming,

Volume 3 Sorting and Searching, Addison Wesley, Reading,

Massachusetts, 1973,

[8] McGeoch, C. C., “Experimental Analysis of Algorithms”,

Notices of the AMS, Vol 48, No. 3, March 2001, pp. 304-311.

[9] Priebe, V., Average-case complexity of shortest-paths

problems, Ph.D. dissertation, University of Saarland, 2001,

available at http://www.mpi-sb.mpg.de/~priebe/diss.pdf.

[10] Schneiderman, Ben, “Jump Searching: A Fast Sequential

Search Technique”, Communications of the ACM, Vol. 21, No.

10, 1978, pp. 831-834.

[11] Sedgewick. R., Algorithms, Addison Wesley, Reading,

Massachusetts, 1983, pp. 12-16.

[12] Tarjan, R. E., Updating a Balanced Search Tree in O(1)

Rotations, Information Processing Letters, Vol. 16, No. 5,

1983, pp. 253-257.
Theoretical Framework for Comparing 

Several Stochastic Optimization Approaches 

James C. Spall, Stacy D. Hill and David R. Stark 

The Johns Hopkins University

Applied Physics Laboratory

11100 Johns Hopkins Road 

Laurel, Maryland 20723-6099 U.S.A. 

E-mail: james.spall@jhuapl.edu

Abstract 

This paper establishes a framework for formal 

comparisons of several leading optimization algorithms, 

establishing guidance to practitioners for when to use or not

use a particular method. The focus in this paper is five 

general algorithm forms: random search, simultaneous 

perturbation stochastic approximation, simulated annealing, 

evolutionary strategies, and genetic algorithms. We

summarize the available theoretical results on rates of

convergence for the five algorithm forms and then use the 

theoretical results to draw some preliminary conclusions on

the relative efficiency. Our aim is to sort out some of the

competing claims of efficiency and to suggest a structure 

for comparison that is more general and transferable than 

the usual problem-specific numerical studies. 

Keywords: Stochastic optimization; rate of convergence;

random search; simultaneous perturbation stochastic

approximation (SPSA); simulated annealing; evolutionary 

computation; genetic algorithms. 1

1. INTRODUCTION 

To address the shortcomings of classical deterministic

algorithms, a number of powerful optimization algorithms

with embedded randomness have been developed. The 

population-based methods of evolutionary computation are 

only one class among many of these available stochastic

optimization algorithms. Hence, a user facing a challenging 

optimization problem for which a stochastic optimization 

method is appropriate meets the daunting task of 

determining which algorithm is appropriate for a given 

problem. This choice is made more difficult by some

dubious claims that have been made about some popular 

algorithms. An inappropriate approach may lead to a large 

waste of resources, both from the view of wasted efforts in

 

This work was partially supported by the JHU/APL IRAD 

Program and U.S. Navy Contract N00024-98-D-8124. An 

expanded version of this paper is available upon request. 

implementation and from the view of the resulting

suboptimal solution to the optimization problem of interest. 

Hence, there is a need for objective analysis of the 

relative merits and shortcomings of leading approaches to

stochastic optimization. This need has certainly been

recognized by others, as illustrated in recent conferences on 

evolutionary computation, where numerous sessions are 

devoted to comparing algorithms. Nevertheless, virtually all

comparisons have been numerical tests on specific 

problems. Although sometimes enlightening, such 

comparisons are severely limited in the general insight they 

provide. Some comparisons for noisy evaluations of a 

simple spherical loss function are given in Arnold (2002, 

Chap. 6); however, some of the competitors were 

implemented in non-standard forms, making the results

difficult to interpret for an analyst using a more 

conventional implementation. Spall (2003) also has a 

number of comparisons (theoretical and numerical) for the 

cases of noise-free and noisy loss evaluations. On the other 

end of the spectrum are the “No Free Lunch Theorems” 

(Wolpert and McReady, 1997), which simultaneously

consider all possible loss functions and thereby draw 

conclusions that have limited practical utility since one 

always has at least some knowledge of the nature of the loss 

function being minimized. 

Our aim in this paper is to lay a framework for a 

theoretical comparison of efficiency applicable to a broad 

class of practical problems where some (incomplete) 

knowledge is available about the nature of the loss 

function. We will consider five basic algorithm forms—

random search, simultaneous perturbation stochastic

approximation (SPSA), simulated annealing (SAN), and 

two forms of evolutionary computation (evolution strategy

and genetic algorithms). The basic optimization problem

corresponds to finding an optimal point θ*

: 

θ* = argmin L( ) , θ∈Θθ
where L(θ) is the loss function to be minimized, Θ is the 

domain over which the search will occur, and θ is a 

p-dimensional (say) vector of parameters. We are mainly 

interested in the case where θ*

 is a unique global minimum.

Although stochastic optimization approaches other than 

the five above exist, we are restricting ourselves to the five 

general forms in order to be able to make tangible progress 

(note that there are various specific implementations of 

each of these general algorithm forms). These five 

algorithms are general-purpose optimizers with powerful

capabilities for serious multivariate optimization problems. 

Further, they have in common the requirement that they

only need measurements of the objective function, not

requiring derivative information (gradient or Hessian) for 

the loss function. 

One might ask whether questions of relative efficiency

are relevant in light of the “no free lunch (NFL)” theorems

of Wolpert and Macready (1997) and others. The NFL 

theorems state, in essence, that the expected performance of 

any pair of optimization algorithms across all possible 

problems is identical. In practice, of course, one is not

interested in solving “all possible problems,” as there is 

usually some prior information about the problems of 

interest and this prior information will affect the algorithm

implementation. Hence, the NFL results may not

adequately reflect the performance of candidate algorithms

as they are actually applied. In other words, some

algorithms do work better than others on problems of 

interest. Nevertheless, the NFL results are an important

backdrop against which to view the results here, providing 

limits on the extent to which one algorithm can be claimed

as “better” than another. 

2. SIMPLE GLOBAL RANDOM SEARCH 

We first establish a rate of convergence result for the 

simplest random search method where we repeatedly

sample over the domain of interest, Θ ⊆ Rp

. This can be 

done in recursive form or in “batch” (non-recursive) form

by simply laying down a number of points in Θ and taking 

as our estimate of θ*

 that value of θ yielding the lowest L 

value. 

To evaluate the rate, let us specify a “satisfactory 

region” S(θ*

) representing some neighborhood of θ*

providing acceptable accuracy in our solution (e.g., S(θ*

) 

might represent a hypercube about θ*

 with the length of

each side representing a tolerable error in each coordinate 

of θ). An expression related to the rate of convergence of 

the above simple random search algorithm is then given by 

 P( ∈S(θ θk

ˆ *

)) = 1 − [1 − P(θnew(k) ∈ S(θ*)]k (2.1) 

We will use this expression in Section 7 to derive a 

convenient formula for comparison of efficiency with other 

algorithms. 

3. SIMULTANEOUS PERTURBATION 

STOCHASTIC APPROXIMATION 

The next algorithm we consider is SPSA. This algorithm

is designed for continuous variable optimization problems. 

Unlike the other algorithms here, SPSA is fundamentally

oriented to the case of noisy function measurements and 

most of the theory is in that framework. This will make for 

a difficult comparison with the other algorithms, but

Section 7 will attempt a comparison nonetheless. The SPSA 

algorithm works by iterating from an initial guess of the 

optimal θ, where the iteration process depends on a highly

efficient “simultaneous perturbation” approximation to the 

gradient g(θ) ≡ ∂L(θ)/∂θ . 

Assume that measurements y(θ) of the loss function are 

available at any value of θ: 

y(θ) = L(θ) + noise . 

For example, in a Monte Carlo simulation-based 

optimization context, L(θ) may represent the mean response 

with input parameters θ, and y(θ) may represent the 

outcome of one simulation experiment at θ. In some

problems, exact loss function measurements will be

available; this corresponds to the noise = 0 setting (and in

the simulation example, would correspond to a 

deterministic⎯non-Monte Carlo⎯simulation). Note that 

no direct measurements (with or without noise) of the 

gradient of L(θ) are assumed available. 

The SPSA procedure is in the general recursive SA 

form: 

) , (3.1) ˆ ˆ ( ˆ ˆ k 1 k k k k θ + = θ −a g θ

where is the estimate of the gradient g(θ) at the 

iterate based on the above-mentioned measurements of 

the loss function and a

) ˆ ˆ ( k k g θ

θk

ˆ

k > 0 is a “gain” sequence. This 

iterate can be shown to converge under reasonable 

conditions (e.g., Spall, 1992, and Dippon and Renz, 1997, 

for local convergence; Maryak and Chin, 2001, for global

convergence). The essential basis for efficiency of SPSA in

multivariate problems is due to the gradient approximation,

where only two measurements of the loss function are 

needed to estimate the p-dimensional gradient vector for 

any p; this contrasts with the standard finite difference 

method of gradient approximation, which requires 2p

measurements. 

Most relevant to the comparative analysis goals of this 

paper is the asymptotic distribution of the iterate. This was 

derived in Spall (1992), with further developments in Chin

(1997), Dippon and Renz (1997), and Spall (2000). 

Essentially, it is known that under appropriate conditions, 

 kβ/2( − θ θk

ˆ *

) ⎯⎯⎯→ N(μ, Σ) as k → ∞ , (3.2) dist
where β > 0 depends on the choice of gain sequences (ak

and ck), μ depends on both the Hessian and the third 

derivatives of L(θ) at θ*

 (note that in general, μ ≠ 0 in

contrast to many well-known asymptotic normality results 

in estimation), and Σ depends on the Hessian matrix at θ*

and the variance of the noise in the loss measurements. 

Given the restrictions on the gain sequences to ensure 

convergence and asymptotic normality, the fastest 

allowable value for the rate of convergence of to θ θk

ˆ *

 is 

k

−1/3. This contrasts with the fastest allowable rate of k−1/2

for gradient-based algorithms such as Robbins-Monro SA. 

Unfortunately, (3.2) is not directly usable in our

comparative studies here since the other three algorithms

being considered here appear to have convergence rate

results only for the case of noise-free loss measurements. 

The authors are unaware of any general asymptotic

distribution result for the noise-free case (note that it is not

appropriate to simply let the noise level go to zero in (3.2) 

in deriving a result for the noise-free case; it is likely that 

the rate factor β will also change if an asymptotic 

distribution exists). Some partial results, however, are 

available that are related to the rate of convergence. 

Gerencsér (1999) established that the moments 

q q

E k

1/

ˆ *

⎥

⎦

⎤ ⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛ θ −θ converge to zero at a rate of k

−1/2 for 

any q > 0, when ak has the standard 1/k decay rate. More 

recently, Gerencsér and Vágó (2000) established that the 

noise-free SPSA algorithm has a geometric rate of 

convergence when constant gains ak = a are used. In 

particular, for functions having bounded third derivatives, 

they show for sufficiently small a, 

ˆ

limsup 1 a.s. k

k k η

∗

→∞

θ − θ

=

for some 0 < η < 1. Gerencsér and Vágó (2000) go further 

for quadratic loss functions by specifying η in terms of a

and the Hessian matrix of L. Unfortunately, even in the 

quadratic case, η is not fully specified in terms of quantities 

associated with L and the algorithm itself (i.e., η depends 

on unknown constants). 

4. SIMULATED ANNEALING ALGORITHMS 

The SAN method (Metropolis et al., 1953; Kirkpatrick 

et al., 1983) was originally developed for optimization over 

discrete finite sets. The Metropolis SAN method produces a 

sequence that converges in probability to the set of global 

minima of the loss function as Tk, the temperature, 

converges to zero. 

Gelfand and Mitter (1993) present a SAN method for 

continuous parameter optimization. They obtained discretetime recursions (which are similar to a stochastic 

approximation algorithm) for Metropolis-type SAN 

algorithms that, in the limit, optimize continuous parameter 

loss functions. 

Furthermore, like SPSA, SAN has an asymptotic 

normality result (but unlike SPSA, this result applies in the 

noise-free case). Let H(θ*

) denote the Hessian of L(θ) 

evaluated at θ*

 and let Ip denote the p × p identity matrix. 

Yin (1999) showed that for bk = (b/(k

γ

log (k

1−γ + B0) )1/2, 

[log (k

1−γ + B0) ]1/2( ˆ

θk - θ*) → N(0, Σ) in distribution, 

where SH + HT

S + (b/a)I = 0. 

5. EVOLUTIONARY COMPUTATION: 

EVOLUTIONARY STRATEGIES 

There are three general approaches in evolutionary

computation (EC), namely Evolutionary Programming 

(EP), Evolutionary Strategies (ES) and Genetic Algorithms

(GA). All three approaches work with a population of 

candidate solutions and randomly alter the solutions over a 

sequence of generations according to evolutionary 

operations of competitive selection, mutation and

sometimes recombination (reproduction). The fitness of 

each population element to survive into the next generation 

is determined by a selection scheme based on evaluating 

the loss function for each element of the population. The 

selection scheme is such that the most favorable elements 

of the population tend to survive into the next generation 

while the unfavorable elements tend to perish. 

The principle differences in the three approaches are the 

selection of evolutionary operators used to perform the 

search and the computer representation of the candidate

solutions. EP uses selection and mutation only to generate

new solutions. While both ES and GA use selection, 

recombination and mutation, recombination is used more 

extensively in GA. A GA traditionally performs 

evolutionary operations using binary encoding of the 

solution space, while EP and ES perform the operations 

using real-coded solutions. The GA also has a real-coded 

form and there is some indication that the real-coded GA 

may be more efficient and provide greater precision than 

the binary-coded GA. The distinction among the three 

approaches has begun to blur as new hybrid versions of EC 

algorithms have arisen. 

Global convergence results can be given for a broad 

class of problems, but the same cannot be said for 

convergence rates. Both Beyer (1995) and Rudolph 

(1997a) examine ES algorithms that include selection, 

mutation and recombination. The function analyzed in both 

cases is the classic spherical fitness function L(θ) = ||θ||2

whose exact solution is of course known. Convergence 

rates based on the spherical fitness function are somewhat

useful, if it is assumed that the sphere approximates a local

basin of attraction. A number of other convergence rate

results are also available for that fitness function, for 

example Qi and Palmeiri (1994) for real-valued GA. The 

most practically useful convergence rates for EC algorithms

seem to be for the class of strongly convex fitness 
functions. The following theorem due to Rudolph (1997b) 

is an application of a more general result by Rappl (1989). 

The theorem will be the starting place for the specific 

convergence rate result that will be used for comparison in 

Section 7. 

An EC algorithm has a geometric rate of convergence if 

and only if E[ −L(θ *

Lk *)] = O(ηk) where η ∈ (0, 1) is called

the convergence rate. Under conditions, the convergence 

rate result for a (1, λ)-ES using only selection and mutation 

on a (K, Q)-strongly convex fitness function is geometric 

with a rate of convergence 

η = (1 – Q 2 Mλ, p 2

) 

where Q is a constant, = E[Β M λ, p λ:λ]>0, and where Βλ:λ

denotes the maximum of λ independent identically

distributed Beta random variables. The computation of Mλ,p

is complicated since it depends on both the number of 

offspring λ and the problem dimension p. Asymptotic

approximations are available and will be shown next. 

Assuming p is fixed and λ→ ∞ then ≈ (2 p Mλ, p

−1

log 

λ)

1/2. To extend this convergence rate from a (1, λ)-ES to a 

(Npop, λ)-ES, note that each of the Npop parents generate

λ/Npop offspring. Then the convergence rate for the 

(Npop, λ)-ES where offspring are only obtained by mutation 

is 

η ≤ [1 – (2p−1

log(λ/Npop))/Q2] 

for (K, Q)-strongly convex functions. 

6. EVOLUTIONARY COMPUTATION: GENETIC 

ALGORITHMS 

As discussed in Stark and Spall (2001), it is possible to

cast the GA in the framework of Markov chains. This

allows for a rate of convergence analysis. Consider a GA 

with a population size of N. Further, suppose that each 

population element is a binary string of length b bits. 

Hence, there are 2b

 possible strings for an individual

population element. Then the total number of possible 

populations is given by

pop

( 2 1)

(2 1)! !

b

b

N N

N

+ − ! ≡ − . 

It is possible to construct a Markov transition matrix Π that 

provides the probability of transitioning from one

population of size N to another population of the same size. 

This transition matrix is Npop × Npop. An individual element

in the transition matrix can be computed according to the 

formulas in Stark and Spall (2001) (see also Suzuki, 1995). 

These elements depend in a non-trivial way on the 

population size, crossover rate, mutation rate, and number 

of elements considered “elite.” 

Of primary interest in analyzing the performance of GA 

algorithms using Markov chains is the probability of 

obtaining a population that contains the optimum ∗θ . Let 

πk be an N × 1 vector having j

th component, πk(j), equal to

the probability that the k

th generation will result in

population j. From basic Markov chain theory, 

Tπk = 1

Tπk− Π = 0T k π Π

where π0 is an initial probability distribution. 

The stationary distribution of the GA is then given by 

0 lim lim TTT

k k k →∞ →∞

k π ≡ π = π Π . 

Further, under standard ergodicity assumptions for 

Markov chains, π satisfies T T π = π Π . This equation 

provides a mechanism for solving directly for the stationary

distribution (e.g., Iosifescu, 1980, pp. 123−124). 

Unfortunately, from a practical view, the Markov chain 

approach has a significant deficiency. The dimension N

grows very rapidly with increases in the number of bits b

and/or the population size N. A perhaps more intuitive 

estimate of the size of Npop can be obtained by Stirling’s 

Approximation as follows:

2 1 1/ 2

pop

2 1 1 1 2 1 1

2 1 2 1

N b b

b b

N N

N N

− ⎛ ⎞ − ⎛ ⎞ ⎛

≈ π ⎜ ⎟ + + + ⎜ ⎟ ⎜ ⎝ − ⎠ ⎝ − ⎠ ⎝ ⎠

⎞

⎟

Thus far, our analysis using the above approach has been 

restricted to scalar θ systems (requiring fewer bits b than a 

multivariate system) and low Npop. 

7. COMPARATIVE ANALYSIS 

7.1 Problem Statement and Summary of Efficiency 

Theory for the Five Algorithms 

This section uses the specific algorithm results in

Sections 2 to 6 above in drawing conclusions on the 

relative performance of the five algorithms. There are 

obviously many ways one can express the rate of 

convergence, but it is expected that, to the extent they are 

based on the theory outlined above, the various ways will 

lead to broadly similar conclusions. We will address the 

rate of convergence by focusing on the question: 

With some high probability 1− ρ (ρ a small number), 

how many L(⋅) function evaluations, say n, are needed 

to achieve a solution lying in some “satisfactory set” 

S(θ*

) containing θ*? 

With the random search algorithm in Section 2, we have 

a closed form solution for use in questions of this sort while

with the SPSA, SAN, and EC algorithms of Sections 3 

through 5, we must apply the existing asymptotic results, 

assuming that they apply to the finite-sample question 

above. For the GA, there is a finite sample solution using 

the Markov chain approach. For each of the five 

algorithms, we will outline below an analytical expression
useful in addressing the question. After we have discussed 

the analytical expressions, we present a comparative 

analysis in a simple problem setting for varying p. 

Random Search 

We can use (2.1) to answer the question above. Setting 

the left-hand side of (2.1) to 1 − ρ and supposing that there 

is a constant sampling probability P*

 = P(θnew(k) ∈ S(θ*)) ∀

k, we have 

log(1 )

log * P

n −

ρ = . (7.1) 

Simultaneous Perturbation Stochastic Approximation 

From the fact that SPSA uses two L(θ*) evaluations per 

iteration, the value n to achieve the desired probability for 

k

ˆ

θ ∈ S(θ*) is then

3 2 ( ) 2 ⎟

⎠

⎞ ⎜

⎝

⎛

δ

σ = s

d p n

where from standard N(0, 1) distribution tables, there exists

a displacement factor, say d(p), such that the probability 

contained within ± d(p) units contains probability amount 

(1 − ρ)

1/p

. We are interested in the k such that 2d(p)σ/k

1/3 = 

δs = (the common length of a side in a p-fold 

hypercube). 

+ −

i − i s s

Simulated Annealing

The value n to achieve the desired probability for 

∈S(θ θk

ˆ *

) is 

2 1 2 ( ) log . 1

d p n s

⎛ ⎞ σ = ⎜ ⎟ − γ ⎝ ⎠ δ

Evolutionary Strategy 

As discussed in Section 6, the rate-of-convergence 

results for algorithms of the evolutionary computation type 

are not as well developed as for the other three algorithms

of this paper. Theorem 6.1 gives a general bound on 

E[L( ) − L(θ θk

ˆ *

)] for application of a (N, λ)-ES form of EC 

algorithm to strongly convex functions. A more explicit

form of the bound is available for the (1, λ)-ES. 

Unfortunately, even in the optimistic case of an explicit 

numerical bound on E[L( ) − L(θ θk

ˆ *

)], we cannot readily

translate the bound into a probability calculation for ∈

S(θ

θk

ˆ

*

), as used above (and, conversely, the asymptotic

normality result on for SPSA and SAN cannot be 

readily translated into one on L( ) since ∂L/∂θ = 0 at 

θ

θk

ˆ

θk

ˆ

*

⎯see, e.g., Serfling, 1980, pp. 122−124—although 

Lehmann, 1983, pp. 338−339 suggests a possible means of 

coping with this problem via higher-order expansions). So, 

in order to make some reasonable comparison, let us 

suppose that we can associate a set S(θ*

) with a given 

deviation from L(θ*

), i.e., S(θ*) = S(θ*, ε) ={θ: L( ) −

L(θ

θk

ˆ

*

) ≤ ε} for some prespecified tolerance ε > 0. As 

presented in Rudolph (1997b), E[L( ) − L(θ)]≤ c θk

ˆ k

 for 

sufficiently large k, where c is the convergence rate in

Section 6. Then by Markov’s inequality, 

1 − P( ∈S(θ θk

ˆ *

)) ≤

ε

θ ) − (θ*)] ˆ E[L( k L

≤

ε

k

c

, (7.2) 

indicating that P( ∈S(θ θk

ˆ *

)) is bounded below by the ES 

bounds mentioned in Section 5. 

The full version of the paper employs Markov’s 

inequality and the bound in Rudolph (1977b) to show that 

there are λ evaluations of the fitness function for each 

generation k so that n = λk, where 

k = 

⎥

⎦

⎤ ⎢

⎣

⎡ − λ

ρ − ε

log( / ) 2 log 1

log log(1/ )

2 N

pQ

. 

Genetic Algorithm 

As mentioned in Section 6, while the GA has a relatively 

clean theory that applies in both finite and asymptotic 

samples, there are significant challenges in computing the 

elements of the Markov transition matrix Π. The number of 

possible states—corresponding to the number N of possible 

populations—grows extremely rapidly with the number of 

population elements N or the number of bits b. The 

computation of the Npop × Npop transition matrix Π quickly

overwhelms even the most powerful current personal

computers. 

Nevertheless, in principle, the Markov structure is

convenient for establishing a convergence rate for the GA. 

The full version of the paper provides value for n. 

7.2 Application of Convergence Rate Expressions for 

Varying p

We now apply the results above to demonstrate relative 

efficiency for varying p. Because the GA result is 

computationally explosive as p gets larger (requiring a 

larger bit string length and/or population size), we restrict

the comparison here to the four algorithms: random search, 

SPSA, SAN and ES. Let Θ = [0, 1]p

 (the p-dimensional 

hypercube with minimum and maximum θ values of 0 and 

1 for each component). We want to guarantee with 

probability 0.90 that each element of θ is within 0.04 units 

of the optimal. Let the (unknown) true θ, θ*

, lie in (0.04,

0.96)p

. The individual components of θ* are . Hence, * θi
* * * * * 1 1 2 2

* *

( ) [ 0.04, 0.04] [ 0.04, 0.04] ...

[ 0.04, 0.04] . p p

S θ = θ − θ + × θ − θ + ×

× θ − θ + ⊂ Θ

Table 7.1 is a summary of relative efficiency for the 

setting above for p = 2, 5, and 10; the efficiency was 

normalized so that all algorithms performed equally at 

p = 1, as described below. The numbers in Table 7.1 are the 

ratios of the number of loss measurements for the given 

algorithm over the number for the best algorithm at the 

specified p; the highlighted values 1.0 indicate the best

algorithm for each of the values of p. To establish a fair 

basis for comparison, we fixed the various parameters in

the expressions above (e.g., σ in SPSA and SAN, ρ for the 

ES, etc.) so that the algorithms produced identical

efficiency results for p = 1 (requiring n = 28 measurements 

to achieve the objective outlined above). These parameters 

do not explicitly depend on p. We then use these parameter 

settings as p increases. 

Table 7.1. Ratios of loss measurements needed relative to

best algorithm at each p for 1 ≤ p ≤ 10 

p = 1 p = 2 p = 5 p = 10 

Rand. Search 1.0 11.6 8970 2.0×109

SPSA 1.0 1.5 1.0 1.0

SAN 1.0 1.0 2.2 4.1

ES 1.0 1.9 1.9 2.8

Table 7.1 illustrates the explosive growth in the relative 

(and absolute) number of loss evaluations needed as p 

increases for the random search algorithm. The other 

algorithms perform more comparably, but there are still 

some non-negligible differences. For example, at p = 5, 

SAN will take 2.2 times more loss measurements than

SPSA to achieve the objective of having inside S(θ*) 

with probability 0.90. Of course, as p increases, all 

algorithms take more measurements; the table only shows 

relative numbers of function evaluations (considered more 

reliable than absolute numbers). 

θk

ˆ

This large improvement of SPSA and SAN relative to 

random search may partly result from the more restrictive 

regularity conditions of SPSA and SAN (i.e., for formal 

convergence, SPSA assumes a several-times-differentiable 

loss function) and partly from the fact that SPSA and SAN 

work with implicit gradient information via gradient

approximations. The performance for ES is quite good. The 

restriction to strongly convex fitness functions, however, 

gives the ES in this setting a strong structure not available 

to the other algorithms. It remains unclear what practical 

theoretical conclusions can be drawn on a broader class of 

problems. 

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Measuring the Performance of Automated Planning Systems

Dana Nau

Department of Computer Science

and Institute for Systems Research

University of Maryland,

College Park, MD 20742, USA

email: nau@cs.umd.edu

Malik Ghallab

LAAS-CNRS

7, Avenue du Colonel Roche

31077, Toulouse, cedex, France

email: Malik.Ghallab@laas.fr

ABSTRACT

In this paper, we describe existing performance measures for automated planning algorithms, and discuss the limitations and biases

inherent in those performance measures. We point out the importance

of developing a performance measure that explicitly the restrictive assumptions on which a planning algorithm depends, and we propose a

composite performance measure based on three factors:

• the scope of the planning algorithm: which set of restrictive assumption are needed and which can be lifted,

• the control knowledge and tuning required for each planning domain,

• the size of the problems that can be solve in a reasonable amount of

time in each area of its scope (i.e., for each combination of relaxed

assumptions it can handle).

KEYWORDS: automated planning, AI planning, performance

measurement

1. INTRODUCTION

Great strides have been made in automated planning during the past few years, and the technology is becoming mature enough to be useful in a variety of demanding applications,

ranging from controlling space vehicles such as Deep Space 1

[6] to playing the game of bridge [31]. Successes such as these

are creating a great potential for synergy between theory and

practice: observing what works well in practice can lead to better theories of planning, and better theories can lead to better

performance in practical applications.

Despite this potential, there currently is a substantial gap

between theoretical and application-oriented work. The theoretical work tends to be rather narrow in scope, focusing on

highly restricted cases such as classical planning, with the most

common performance measure being the speed of the planner’s

combinatorial search. The application-oriented work generally

depends on ad hoc application-specific programming efforts,

search techniques, and measures of performance.

For most planning systems, presentations of the planning

algorithm may discuss some of the assumptions and restrictions

explicitly—but usually the algorithm will also depend on additional assumptions and restrictions that are tacit in the repreFigure 1: A simple conceptual model for planning. Σ is a statetransition system, as described in the text.

sentation rather than explicit. As a consequence, it is often very

difficult to judge whether a planning algorithm can be useful for

real-world problem solving, and it is often even more difficult

to tell whether an application-specific planning algorithm can

be generalized to work in anything other than the specific application for which the algorithm has been written. Better ways

are needed to judge the scope and generalizability of planning

algorithms and techniques.

As a step toward meeting that need, we describe a general

conceptual model for planning, and use it to classify and discuss the kinds of restrictive assumptions that are often made

in automated planning research. We believe that with suitable

refinement, such a classification will provide a useful performance measure for automated planning algorithms, by providing a way to give a clearer account of what restrictions a planning algorithm requires.

2. CONCEPTUAL MODEL FOR PLANNING

Since planning is concerned with choosing and organizing

actions for changing the state of a system, a conceptual model

for planning requires a general model for a dynamic system.

This model, shown in Figure 1, includes three components:

• A state-transition system Σ that evolves as specified by its

state-transition function γ, according to the events and ac1
Experimental Studies of Integrated Cognitive Systems

Pat Langley

Computational Learning Laboratory

Center for the Study of Language & Information

Stanford University, Stanford, CA 94305 USA

langley@csli.stanford.edu

Elena Messina

National Institute of Standards & Technology

100 Bureau Drive, Mail Stop 8230

Gaithersburg, MD 20899 USA

elena.messina@nist.gov

Abstract—In this paper, we examine the issues that arise

in the experimental study of integrated cognitive systems. We

review the reasons why such artifacts are difficult to evaluate,

then consider some dependent measures that can be used

to characterize their behavior. Next we discuss independent

variables that can influence this behavior, in particular features

of the domain and characteristics of the system, including

its knowledge and experience. We then turn to domains and

testbeds that support experiments with such systems, giving

examples of some promising candidates. We conclude with

a discussion of the scientific goals of experimentation, which

involve understanding the mapping from domain and system

characteristics onto behavior.

I. Introduction and Motivation

For more than a decade, research in artificial intelligence

has relied on experimentation as a key element in evaluation. Machine learning was perhaps the first subdiscipline

to adopt systematic experiments (e.g., Kibler & Langley,

1988), but their use has spread throughout the broader

community (e.g., Cohen, 1995). Today, experiments are

the primary means by which AI researchers evaluate their

methods, and the experimental techniques as mature and

well understood.

However, the experimental study of integrated cognitive

systems is less well established and clearly needs more

development. The reasons should be clear from the phrase

itself, which reflects the nature of the intelligent artifacts

being constructed. First, it is inherently more difficult to

evaluate systems than component algorithms, since they

are harder to construct and analyze. Second, it is more

challenging to run experiments with cognitive systems,

since they rely on complex, multi-step reasoning rather

than simple classification or reactive control. Finally,

evaluating claims about integrated systems is problematic

because it involves the examination of interactions among

their components. Together, these distinctive factors have

slowed the development of an experimental method for

such complex entities.

In this paper, we propose an experimental framework

that is appropriate for the study of integrated cognitive systems. In the next section, we discuss basic and

higher-order dependent measures that can arise in such

experiments. After this, we consider three main classes of

independent factors that can influence system behavior,

then turn to domains and testbeds that would support

the experimental evaluation of such systems. In closing,

we discuss the broader scientific goals of experimentation,

which aim not to show superiority but to identify reasons

for observed behaviors.

II. Dependent Measures of System Behavior

As scientists, we are concerned with understanding

the behavior of integrated cognitive systems, which in

turn means that we require ways to observe and characterize this behavior. In this context, it is important

to distinguish between between metrics and dependent

measures. These terms are closely related, but the first is

typically associated with prescriptive benchmarks that are

used to determine one system’s superiority other another,

whereas the second is generally associated with systematic

experiments that aim at scientific understanding. The

comments that follow are relevant to both approaches

to evaluation, but our focus here is on the latter, which

we think is far more appropriate for the current stage

of the field. We organize our treatment into three broad

categories: basic measures, averaged metrics, and higherorder variables.

A. Basic Measures of System Behavior

The existing literature reports a variety of basic measures that are relevant to integrated cognitive systems.

These provide the simplest ways to describe the observed

behavior of an intelligent construct. We should clarify

that behavior always occurs in the context of some task,

whether provided externally or generated by the agent

itself, and some situation, whether it involves the agent’s

physical environment or its mental state. We will refer to

this context informally as the problem that the agent is

attempting to solve.

Perhaps the most straightforward behavioral measure

concerns whether the agent succeeds or fails at handling a

given problem. For example, a cognitive system may prove

or fail to prove a geometry theorem, it may or may not

solve a novel puzzle, it may or may not deliver a package

to a specified address, and it may win or lose a given

game. This measure offers only one bit of information,

but it may still be valuable when combined with other

results, as we will see shortly.

However, other problem-related measures provide more

detail. One such metric is the efficiency or speed with

which the cognitive system handles a given problem.
For instance, one can count the number of states in a

problem space considered during a geometry proof, the

time it takes a driver to deliver a package, and the

number of moves until checkmate in a chess game. Such a

dependent variable gives information about the cognitive

or physical efficiency with which the agent handles a

particular problem.

Of course, some paths to success are more desirable than

others, so we may also want to measure the quality of the

cognitive system’s solution to a problem. For example, a

geometry proof may have few or many steps and thus

be more or less elegant, a package deliverer may drive

safely and politely or dangerously and impolitely on his

way to an address, and a chess player may lose only

a few unimportant pieces or many important ones in

defeating an opponent. Metrics of this sort offer details

about the desirability of the cognitive agent’s behavior in

accomplishing a given task.

B. Combined Measures of Behavior

The field of statistics tells us we should not draw conclusions from individual cases, but rather that we should

rely on multiple samples. We can then combine the results

from these samples and calculate a more robust dependent

variable. Taking the average of sampled measurements

is the most common and obvious combination scheme,

but calculating cumulative scores is another possibility.

The important thing is that, by combining measures for

different samples, we can partly cancel out variation due

to unknown or unavailable factors, and thus increase the

chance of meaningful results.

Naturally, this approach requires some population from

which to draw samples, typically different problems from

within a single domain, although sampling from across

domains is also possible. For instance, we might present

the cognitive system with different geometry theorems to

prove, ask it to deliver packages to distinct addresses or

even in different cities, and confront it with different chess

opponents or even chess-like games with alternative rules.

The population from which one draws samples determines

the generality of one’s conclusions about the cognitive

system’s behavior. We may suspect that the agent can

prove theorems not only in geometry but also in algebra,

but sampling from the former domain provides no evidence

for the latter. An empirical study should state clearly

the population being sampled, ideally in formal terms

but always in enough detail that others can replicate the

sampling process.

We should note that combined measures of behavior

offer more than guards against unknown factors and

random noise. This approach also lets one convert qualitative measures, such as success or failure on a problem,

into quantitative ones, such as the percentage or total

number of problems solved. This makes them especially

useful for researchers who want to make claims about

new functionality, which at first glance appear to involve

only qualitative evidence, but which can be handled in

quantitative terms with averaged, cumulative, or other

combined measurements of system performance.

C. Higher-Order Measures of Behavior

Although combined measures guard against unknown

influences and offer quantitative variables, they still

present only a small window into often complex behavior.

Metrics that average across domains improve the situation,

since they provide information about a cognitive system’s

broader generality, but more sophisticated responses are

certainly possible.

For instance, we might plot the dependent measure for

a novel system against the same measure for a baseline

or control system, with each point summarizing the two

systems’ behaviors on a distinct problem. We can then

use regression to fit a line to the points, which gives

both a slope and an intercept as higher-order measures.

A positive intercept means the novel system does better

than the control even on easy problems, whereas a slope

greater than one means it scales to difficulty better than

the baseline system.

Another example, which we will discuss more later,

involves learning curves, in which one plots a behavioral

measure like efficiency or quality against the number of

training cases a learning system has encountered. Such

curves typically have either an exponential or sigmoid

shape, so that linear regression is not appropriate, but we

can fit them with other parametric forms. These produce

higher-order measures for the system’s performance at the

outset, its rate of improvement as a function of experience,

and its asymptotic performance.

Both of these examples involve some form of variation,

though this need not be systematic. In general, whenever

one collects simple measures of a cognitive system’s

behavior under a number of distinct conditions, these can

be used to calculate higher-order measures that summarize

its behavioral characteristics across the conditions from

which the samples were taken.

III. Influences on System Behavior

A scientific experiment should do more than measure

a system’s behavior under one or more condition. The

goal of experimentation is to understand the factors that

influence the behavior, which means one should measure

the dependent variables in multiple situations that differ

along some dimension. Such a factor is often referred to

as an independent variable, since one can typically vary

it independently of others. As with dependent measures,

different independent variables can reveal different facets

of the system under study. In this section, we examine

three broad classes of controllable factors that are appropriate for the experimental evaluation of integrated

cognitive systems.
A. Characteristics of the Task and Domain

One important type of independent variable concerns

aspects of the problem domain and the tasks which

occur within it. The simplest version of this idea involves

collecting multiple samples for an experimental condition,

which we have already discussed above. For studies with an

intelligent system, this means running the system multiple

times on different problems from a domain, and then

combining the results in some fashion. For this purpose,

one draws sample tasks from some distribution over the

problem domain. This may involve specifying a fixed set of

problems or tasks, but another strategy involves creating

a generator that can produce sample problems. In either

case, one should state the relation between these samples

and the broader class of problems over which one hopes

to generalize.

An important variation on this idea involves running

the system on problems from different domains to ensure

its generality. If we are interested in this central issue, then

it is essential to demonstrate successful behavior not only

across different tasks within the same domain, but across

a variety of distinct domains. For instance, most AI work

on game playing has focused on a single game like chess,

which Pell (1996) argues has produced systems that are

optimized for that domain but do not demonstrate general

intelligence. Instead, he defined an entire class of chess-like

games and developed a system that plays reasonably when

given information about their board, pieces, and rules.

Such studies ensure generality, but they do not by

themselves reveal the reasons for variations in system

behavior. For this, we must examine the relation between

problem difficulty and response. We can order problems

by the results they produce on some behavioral measure

like problems solved or efficiency of solutions, but this

does not provide much insight. Ideally, one should vary

experimentally the problem difficulty and examine its

effects on system behavior. This in turn requires an

analysis of the domain that suggests what factors influence

the difficulty of problems.

Kibler and Langley (1998) provide an early domain

analysis for machine learning. They propose a number

of factors that affect the difficulty of induction tasks,

including the complexity of the target concept, the number

of irrelevant features, and the amount of noise in the

training data. Their analysis focused on classification, but

they mention analogous difficulty factors for other areas,

such as the regularity of problem spaces and the structure

of target grammars. One factor they overlooked was the

rate of environmental change, which can pose a challenge

for any learning system.

Studies that vary problem difficulty typically rely on

synthetic domains to control this factor, but Langley

(1996) warns against their casual use. Synthetic problems

give one fine-grained control over domain characteristics,

which can let one determine how these factors influence

behavior. But one must be careful to ensure that these

problems are sufficiently similar to ones which arise in

natural domains that they remain relevant. Nor should

one utilize synthetic problems except to support the

systematic variation of domain features. In general, a wellbalanced experimental program includes studies with both

synthetic domains, to provide insight, and natural ones,

to ensure relevance.1

B. Characteristics of the System

If we want to understand why a cognitive system

behaves well or poorly, then we must vary characteristics

of that system. The simplest version of this idea involves

replacing the entire system with another, as typically

occurs in competitions. Unfortunately, even when one

system behaves uniformly better than another, which

seldom happens, such comparisons provide no insight into

the reasons for their behavioral differences.

One form of finer-grained study involves varying the

parameters associated with the cognitive system and

measuring the effect on its behavior. For instance, one

might alter the depth to which search occurs in a system

that proves geometry theorems, the utility function used to

guide a driving system’s choices, and the relative values

of pieces in a chess player. Such experiments can lead

to conclusions about the importance of a parameter to

system behavior, which may be unchanged across a wide

range of parameter values, change slowly as the parameter

varies, or produce sudden shifts at certain threshold

values. Parametric studies may also detect interactions

among settings that indicate nonlinear effects.

Another experimental approach compares the basic

system’s behavior with that when one or more of its

modules has been removed. For example, one might

compare a driving agent with and without a component for

planning routes. Similarly, one might examine a geometry

theorem prover with and without a module that learns

from previous proofs or a chess player that can or cannot

analyze its opponent’s strategy. Such lesion studies let one

draw conclusions about the contribution of the removed

components to the system’s overall behavior. They can be

especially useful in understanding integrated cognitive systems, since they can reveal interactions among modules.

For instance, inclusion of planning and learning abilities in

a driving system may provide benefits greater than their

sum when used alone.

C. Knowledge and Experience of the System

Cognitive systems rely centrally on knowledge about

a domain to make inferences and generate candidate

solutions to the problems they encounter. Knowledge is

just as important a determinant of behavior as the domain

and system characteristics. However, the precise impact of

1Unfortunately, this mixture is quite rare in the literature, presumably because it requires extra effort from experimenters, but this

does not reduce its importance for the study of intelligent systems.
knowledge on a specific intelligent system is an open issue

that can be studied experimentally.

The methodology of lesion studies, which we discussed

above in the context of system components, can be

adapted easily to knowledge. We can run a geometry theorem prover with and without access to lemmas, we can ask

a driver to deliver packages with and without a cognitive

map of the city, and we can provide or not provide a chess

player with a library of opening moves. In some cases, such

lesion studies are equivalent to experiments with system

modules, since certain components may be included only

to utilize a specific type of knowledge. But the modules

of many cognitive systems have more general abilities, so

that running them with and without access to knowledge

can uncover its importance independent of the component

processes themselves.

Of course, the knowledge utilized by a cognitive system

does not usually come in large packages, but rather in

small, modular knowledge elements. As a result, one can

also vary systematically the amount of knowledge available

to the agent of a given type. For instance, a theorem

prover may have access to many or few lemmas, a driver

responsible for delivering packages may have a more or

less complete cognitive map, and a chess player may know

about different numbers of opening moves. Experiments

that treat knowledge in this manner produce graphs that

plot behavioral measures like efficiency and quality against

knowledge. These can also provide higher-order metrics

that describe the rate of improvement per knowledge

element, as we discussed earlier.

For cognitive systems that learn, we can examine the

effects of experience in a similar manner. Here one relates

the number of problems solved, the time spent by the

agent, or other measures of experience to the standard

behavioral variables. For example, one can graph the

percentage of geometry theorems proved as a function of

the number of previous efforts, the efficiency of package delivery against the number of earlier trips, and the number

of chess pieces lost against the number of games played.

As mentioned earlier, such learning curves also provide

higher-order information about the rate of improvement

and asymptotic behavior.

IV. Repositories for Cognitive Systems

As we have noted, experimental studies of intelligent

systems require some class of problems on which to

measure behavior, but developing such tasks can be time

consuming and expensive. The natural response is to

develop a common repository of domains and problems

for use by the research community. The earliest example

was the UCI Machine Learning Repository (Blake & Merz,

1998), launched by David Aha in the late 1980s. This

provided a variety of well-documented data sets for the

evaluation of supervised learning systems, and within a

few years it became so popular that most papers on

machine learning utilized it in their experimental studies. Another model came from computational linguistics,

where the annual TREC competitions came to drive many

research efforts and has been imitated by other fields, such

as the AI planning community.

Unfortunately, despite their advantages, repositories

and competitions also have negative aspects. Their very

ease of use can encourage a community to focus only

on the technical issues they represent. For example, the

UCI repository encouraged increased learning research on

classification domains at the expense of work on problemsolving tasks. Moreover, many learning researchers have

adopted a ‘bake-off’ mentality that is concerned only with

improving performance scores over earlier systems, and

competitions like TREC have much the same effect. To

the extent that the contents of repositories come to be

viewed as benchmark problems, they lose their usefulness

for genuine scientific studies.

A. Desirable Characteristics of Testbeds

Nevertheless, a common repository is an obvious means

to encourage and support research on integrated cognitive

systems, so we should consider what characteristics would

make it most useful. Like the UCI repository, it must

include a variety of distinct domains to ensure the generality of experimental results. Moreover, its contents must

be well documented and it must be easy for researchers

to use, with a standardized format or interface to simplify

interaction with different cognitive systems. These are key

characteristics of existing repositories that are well worth

replicating in new ones.

However, the repository should support experiments

with integrated cognitive systems in ways that previous

ones have not. For example, it should not contain data

sets like the UCI site or the TREC competitions, or even

sets of problems, like the planning competitions. Instead,

it should provide the community with environments or

testbeds in which researchers can evaluate their creations.

Unlike many component AI algorithms, a cognitive system

exists over time and requires some environment in which

to operate. This environment need not be a physical one,

but embodied cognitive systems are perhaps the most

interesting variety, so the repository should contain some

testbeds that support the study of physical agents.

A testbed provides supporting or enabling infrastructure

for work on a given problem domain. Each testbed must

include a definition of the tasks or missions that arise in

its domain, stated in terms of initial situations and the

desired states or objectives. Each domain should support

a range of such tasks and, ideally, come with a problem

generator that researchers can use to produce novel ones.

A testbed provides infrastructure that facilitates experimentation by the community and thus can lead to insights

about alternative approaches. Examples of infrastructural

support include: external databases, such as geographic

information systems, and the means to connecting to
these resources; the controlled capture, replay, halting, and

restart of scenarios; and methods for capturing relevant

performance measures via application programming interfaces, access to variables and parameters, and external

physical instrumentation.

A well-designed testbed for cognitive systems eases their

experimental evaluation, which follows naturally from certain desirable attributes of the infrastructure and problem

set. To assist researchers in evaluating high-level behavior,

it should provide an environment that has little or no

dependence on actuation or sensor processing. In addition,

the infrastructure and problem domain should offer a rich

operating environment, with the ability to model and

control various entities. The testbed should let researchers

vary, in quantifiable ways, the difficulty or complexity

of the environment or mission. Moreover, although the

study of integrated systems is crucial, a testbed should

also support evaluation of component subsystems, such as

reasoning and learning methods, through parametric and

lesion studies.

For domains that involve an external setting, one can

certainly create a physical testbed to support evaluation,

but another option is to develop a realistic simulated environment that can be used by many more research groups at

much lower cost. For example, Jacoff, Messina, and Evans

(2001) describe a physical testbed for evaluating robot

search and rescue, whereas Balakirsky and Messina (2002)

report a simulated environment to support research on

the same problem. Simulated testbeds have an additional

advantage in that they allow easy variation of domain parameters, ranging from details of the environmental layout

to noise in the agent’s sensors. Moreover, they let one

record detailed traces of the intelligent system’s physical

behavior and its mapping onto cognitive state, which in

turn supports detailed analyses and replay starting from

any point along the agent’s behavioral trajectory.

However, as we noted above, testbeds that rely on synthetic domains also come with the danger of irrelevance.

Whenever possible, they should be based closely on a

physical testbed and provide simulations of sufficiently

high fidelity. Wang (2003) describes one such simulated domain that incorporates models, based on a gaming engine

that supports kinematics and dynamics, of the physical

NIST arenas for urban search and rescue. To further

ensure relevance for intelligent systems that sense their

environment, a testbed may provide data sets collected

from real sensors in analogous locations (e.g., Shneier,

2003). Such additions can help retain the advantages of

physical environments while offering the affordability and

ease of simulated ones.

B. Promising Domains and Testbeds

We can clarify the desirable features of testbeds with

some examples. We have already mentioned the search

and rescue domain, for which NIST has developed both

physical and simulated testbeds. The primary task involves searching for survivors in an urban area after

an earthquake or similar disaster. This domain requires

the combination of sensing, planning, and action in an

integrated cognitive system that can recognize humans,

find routes through dangerous areas, and execute its plans

successfully. The testbeds have been in place for a number

of years and have been used effectively in a number of

international competitions.

Another candidate domain involves flying a simulated

aircraft in a military setting. Keeping an airplane aloft

can be a challenging control task, but by itself this

does not require much cognitive activity or integration of

different capabilities. However, Jones et al. (1999) report

a complex environment in which an agent must fly a jet

fighter, distinguish friendly from enemy aircraft, respond

according to established doctrine, and communicate with

other pilots. Their intelligent agent operated within the

ModSAF environment, which was populated by other

aircraft, some controlled by programs and others by

humans. A related set of problems would involve flying

an unmanned reconnaissance vehicle over enemy territory

to gather information while avoiding dangerous areas.

A third challenging domain involves in-city driving. This

raises few problems at the control level, since keeping a

car upright, on the road, and within its lane does not

require much intelligence. But the presence of buildings,

sidewalks, traffic signs and signals, moving and parked

vehicles, and pedestrians make for a very rich environment

that requires the allocation of perceptual attention and

other resources. Moreover, driving can support many distinct high-level tasks, such as delivering packages, tailing

another car unobtrusively, and pulling over vehicles for

moving violations. These all require the integration of

cognitive, perceptual, and motor components in a complex

dynamical setting.

There already exist many simulated driving environments, but few have been developed with the intention

of evaluating intelligent systems. Moriarty and Langley

(1998) report a simulator for highway driving, but this

environment had low fidelity and agents had limited

options. More recently, Choi et al. (2004) describe an incity driving environment, which they have used to evaluate

a cognitive driving agent, that includes many more objects

and a broader range of activities. Balakirsky, Scrapper,

and Messina (in press) are developing another infrastructure, Mobility Open Architecture Simulation and Tools,

that provides well-defined interfaces to the various driving

subsystems and rich visualization at various levels of

resolution. Several organizations are using this system to

test subsystems for vehicle control, but it remains to be

seen whether the environment meets all the requirements

for evaluating an integrated cognitive system.

Both driving and flying involve control of an individual

agent, but an equally important class of domains involve

managing a large set of other agents. Commanding troops

in a battlefield scenario is one example that requires capa-
bilities like monitoring, situation assessment, planning and

scheduling of activities, and allocation of resources. However, interactive strategy games like Civilization have similar characteristics and complexity, and they are familiar to

more people. Aha and Molineaux (2004) are constructing

a framework that simplifies the interface to such games,

and thus will provide a set of related testbeds for the experimental study of integrated cognitive systems. Michael

Genesereth (personal communication, 2004) is developing

a different infrastructure to support an annual competition

in generalized game playing (http://games.stanford.edu/),

with the intent of fostering research efforts on flexible

approaches to intelligent behavior.

V. Concluding Remarks

In the preceding pages, we have considered the dependent measures and independent factors that arise in studying integrated cognitive systems, along with characteristics

of repositories and testbeds to support such experiments.

Before closing, we should situate these comments in

the broader context of scientific experimentation. As in

other fields, the aim of systematic experiments is not

to show that one approach is superior to another but

rather to increase our understanding of complex systems.

Such understanding may also lead to improved artifacts,

but the overriding goal is to produce replicable and

interpretable results that add to our scientific knowledge

about intelligent behavior.

To this end, researchers should not carry out unmotivated comparisons between different systems or environments. In most cases, one should have a clear question

in mind or a specific hypothesis that one wants to test,

and the experimental design should reflect this intention.

Simple demonstrations of functionality and generality are

reasonable when one first develops a cognitive system, but

they should quickly give way to scaling studies that reveal

its ability to handle complexity and to lesion studies that

identify the roles that its components play in determining

overall behavior.

Whenever possible, experimental results should be utilized to test such hypotheses. Because most studies involve

averaging across samples, one should be careful about

drawing conclusions. Statistical tests can be useful for

this purpose, but they are overrated, in that one can

sometimes obtain ‘significant’ differences between experimental conditions even when they are not substantial.

Nor are statistical tests required when differences are

large, although reporting confidence intervals is crucial

for conditions with high variance.

Results that agree with an hypothesis lend it evidence,

though they do not ‘confirm’ it; science can never draw

final conclusions about any situation. Results that diverge

from one’s expectations count as evidence against a claim,

and thus require additional explanation. Negative results

need not imply failure, since they can lead one to alter

assumptions about system behavior and suggest new ways

to test them. The iterative loop of hypothesize and test

is as central the study of intelligent systems as to other

experimental disciplines.

Nevertheless, integrated cognitive systems pose special

challenges that require creative adaptation of standard

experimental methods. We must develop testbeds that

exercise the full capabilities of such systems, rather than

emphasizing tasks that can be handled by simple classification or reactive control. We must study behavior

at the system level, rather than focusing on component

algorithms. Finally, we must design experiments that

illuminate the manner in which the modules of such

systems interact to produce flexible and robust behavior.

Taken together, these steps should let us transform the

study of integrated cognitive systems into a dynamic and

well-balanced experimental science.

Acknowledgements

This research was funded in part by Grant HR0011-04-

1-0008 from Rome Laboratories. Discussions with David

Aha, Michael Genesereth, and Barney Pell contributed to

the ideas presented in this paper.

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tions that it receives. Σ includes a set S of states, a set A

of actions, a set E of events, and a state-transition function

γ : S × A × E → 2

S.

• A controller. Given as input the state s of the system (or more

generally, some observations that give partial knowledge of

the current state), the controller provides as output an action

a according to some plan.

η : S → O that maps S into some discrete set O =

{o1, o2, . . .} of possible observations. The input to the controller is then the observation

• A planner: given as input a description of the system Σ, an

initial situation and some objective, it synthesizes a plan for

the controller in order to achieve the objective.

The planner’s objective can be specified in several different

ways.

1. The simplest specification consists of a goal state sg or

a set of goal states Sg; the objective is achieved by any

sequence of state transitions that ends at one of the goal

states.

2. More generally, the objective is to satisfy some condition

over the sequence of states followed by the system; for

example, one might want to require states to be avoided,

states that the system should reach at some point, and

states that it should stay in.

3. An alternative specification is through a utility function

attached to states, with penalties and rewards, the goal

being to optimize some compound function of these utilities, e.g. sum or maximum, over the sequence of states

followed by the system.

4. Another alternative is to specify the objective as tasks that

the system should perform. These tasks can be defined

recursively, as sets of actions and other tasks.

3. RESTRICTIVE ASSUMPTIONS

The conceptual model in the last section was deliberately

quite general, in order to provide a starting point for describing

a number of restrictive assumptions:

• Assumption A0 (Finite Σ). The system Σ has a finite set of

states.

• Assumption A1 (Fully Observable Σ). The system Σ is

fully observable, i.e., one has complete knowledge about the

state of Σ; in this case the observation function η is the identity function.

• Assumption A2 (Deterministic Σ). The system Σ is deterministic, i.e., for every state s and event or action u,

|γ(s, u)| ≤ 1. If an action is applicable to a state, its application brings a deterministic system to a single other state.

Similarly for the occurrence of a possible event.

• Assumption A3 (Static Σ). The system Σ is static, i.e., the

set of events E is empty. Σ has no internal dynamics; it stays

in the same state until the controller applies some action.1

• Assumption A4 (Attainment Goals). The only kind of goal

is an attainment goal, which is specified as an explicit goal

state sg or a set of goal states Sg. The objective is to find

any sequence of state transitions that ends at one of the goal

states. This assumption excludes, for example, states to be

avoided, constraints on state trajectories, and utility functions.

• Assumption A5 (Sequential Plans). A solution plan to a

planning problem is a linearly ordered finite sequence of actions.

• Assumption A6 (Implicit Time). Actions and events have

no duration, they are instantaneous state transitions. This assumption is embedded in state-transition systems, a model

that does not represent time explicitly.

• Assumption A7 (Off-line Planning). The planner is not

concerned with any change that may occur in Σ while it is

planning; it plans for the given initial and goal states regardless of the current dynamics, if any.

The simplest case, classical planning, combines all eight

restrictive assumptions: complete knowledge about a deterministic, static, finite system with restricted goals and implicit time.

Here planning reduces to the following problem:

Given Σ = (S, A, γ), an initial state s0 and a

subset of goal states Sg, find a sequence of actions ha1, a2, . . . , aki corresponding to a sequence

of state transitions (s0, s1, . . . , sk) such that s1 ∈

γ(s0, a1), s2 ∈ γ(s1, a2), . . . , sk ∈ γ(sk−1, ak),

and sk ∈ Sg.

Since the system is deterministic, if γ is applicable to s then

γ(s, a) contains one state s

0

. To simplify the notation, we

will say γ(s, a) = s

0

rather than γ(s, a) = {s

0}. For this

kind of system, a plan is a sequence ha1, a2, . . . , aki such that

γ(γ(. . . γ(γ(s0, a1), a2), . . . , ak−1), ak) is a goal state.

The assumption about complete knowledge is needed only

at the initial state s0, because the deterministic model allows all

of the other states to be predicted with certainty. The plan is

unconditional, and the controller executing the plan is an openloop controller, i.e., it does not get any feedback about the state

of the system.

Classical planning may appear trivial: planning is simply

searching for a path in a graph, which is a well understood problem. Indeed, if we are given the graph Σ explicitly then there

is not much more to say about planning for this restricted case.

However, it can be shown [14] that even in very simple problems, the number of states in Σ can be many orders of magnitude greater than the number of particles in the universe! Thus

1The name of this assumption is inaccurate, because the plan is intended

precisely to change the state of the system. What the name means is that the

system remains static unless controlled transitions take place.
it is impossible in any practical sense to list all of Σ’s states

explicitly. This establishes the need for powerful implicit representations that can describe useful subsets of S in a way that

both is compact and can easily be searched.

The simplest representation for classical planning is a settheoretic one: a state s is represented as a collection of propositions, the set of goal states Sg is represented by specifying a

collection of propositions that all states in Sg must satisfy, and

an action a is represented by giving three lists of propositions:

preconditions to be met in a state s for an action a to be applicable in s, propositions to assert and propositions to retract from

s in order to get the resulting state γ(s, a) . A plan is any sequence of actions, and the plan solves the planning problem if,

starting at s0, the sequence of actions are executable, producing

a sequence of states whose final state is in Sg.

A more expressive representation is the classical representation:

2

starting with a function-free first-order language L, a

state s is a collection of ground atoms, and the set of goal states

Sg is represented by an existentially closed collection of atoms

that all states must satisfy. An operator is represented by giving

two lists of ground or unground literals: preconditions and effects. An action is a ground instance of an operator. A plan is

any sequence of actions, and the plan solves the planning problem if, starting at s0, the sequence of actions are executable,

producing a sequence of states whose final state satisfies in Sg.

The de facto standard for classical planning is to use some variant of this representation.

4. CLASSICAL PLANNING VERSUS PLANNING

APPLICATIONS

For nearly the entire time that automated planning has existed, it has been dominated by research on classical planning.

For a while, the dominance was so complete that the term

“domain-independent planning system” was used to refer to

planning systems whose scope was that of classical planning,

as if classical planning were capable of representing all possible planning domains.

In reality, it can be proved [14, Chapters 1–3] that classical planning systems are restricted to a very narrow class of

planning domains. This class excludes most problems of practical interest, because most practical planning problems do not

satisfy the restrictions of classical planning. Here are a few examples:

• Process planning for machined parts. Process planning is

an important manufacturing task, and many millions of R&D

dollars have been spent to try to automate it [23]. The state

space consists of the possible states of the workpiece, including the workpiece geometry and various other parameters. The action space consists of the possible ways to modify the workpiece using machining operations. Both spaces

2This has also been called STRIPS-style representation), after an early planning system [27] that used a similar representation scheme.

are effectively infinite [17]. The actions have nondeterministic outcomes due to random variations—but in process planning the outcomes usually are approximated deterministically by the use of machining tolerances [9]. The planner

must consult with CAD modelers to reason about the workpiece geometry, and must query databases to obtain information about the available machines, tooling, fixturing, and

process parameters. With the exception of a few specialized

process-planning tasks such as sheet-metal bending [16] and

NC toolpath generation [28], generative process planning

tools do not work very well and have not achieved significant

industrial use. By far the most widely used process-planning

tools are those that provide information to help expert humans do the process planning. Other approaches, e.g., [3, 8],

illustrate the same trend for planning in other manufacturing

applications.

• Planning declarer play in bridge. At the beginning of play

in a bridge hand, the declarer (the player who chose the trump

suit) needs to develop a plan for how to play the hand. The

outcomes of the declarer’s actions are uncertain, due both to

uncertainty about how the opponents will respond and uncertainty about how they might be able to respond (since the declarer does not know which opponent holds which cards). A

game tree containing all of the possibilities would have about

2.3 × 1024 leaf nodes on the average and about 5.6 × 1044

in the worst case [30, p. 226]. Since most bridge games are

over in just a few minutes, it would not be feasible to explore

any significant fraction of such a game tree. Instead, techniques have been developed that use various combinations

of game-tree search, Monte Carlo simulation, and reasoning

about possible strategies [12, 15, 31]. The resulting programs

can play better than the average human bridge player, but not

as good as the best human players.

• Ship-movement planning. Planning the movements of ships

is important both commercially and militarily [11]. The state

space and action space are effectively infinite: states include

positions and velocities of ships, and actions correspond to

movements of the ships along various routes. Since movements of different ships may occur concurrently, it is important to make sure they do not interfere with each other.

The outcomes and durations of the actions cannot be known

with certainty, because of factors such as weather, currents,

and the behavior of the ships’ operators. Elaborate simulation tools are available to aid in planning ship movements but the planning is still done manually [1]. Similarly,

other transportation-planning applications, such as for railways [2], have focused on interactive approaches for planning.

Many other examples could easily be cited; see for example the

PLANET repository’s “Real-World Planning and Scheduling

page” at hhttp://vitalstatistix.nicve.salford.ac.uk/planet2i.
5. EXISTING PERFORMANCE MEASURES

In this section, we do a quick survey of existing performance measures, and draw several conclusions about the limitations of those measures.

5.1. Survey

Performance measures for classical planners. The existence of a standard representation scheme for classical planning has made it relatively easy to develop large collections of

planning problems on which different planning algorithms can

be compared. In the three international planning competitions

that have occurred so far [24, 4, 22], many hundreds of classical planning problems have been generated, from about fifteen

different planning domains.3 The most common performance

measures have been success rate, speed, and solution size, i.e.,

the fraction of problems solved, the CPU time needed to solve

them, and the size of the solution found (the latter two are normally measured as a function of the problem size). From these

measures, one can get a rough idea of the size of the problems

that a planner can solve in a reasonable amount of time.

A partial generalization. The 2002 International Planning

Competition [22] included several collections of planning problems that did not satisfy all of the restrictions of classical planning. In these problems, Restrictions A0, A4, and A6 were

weakened, by generalizing the planning language to include numeric computations and optimization goals.4

Although these generalizations may seem rather modest,

they demonstrated some interesting things about the nature of

classical planning, as discussed below.

For each of the planners in the competition, the planning

engine was problem-independent, and the input for each planning problem included the initial state, the goal or objective

to be achieved, and the set of operators for the problem domain. However, the planners varied in terms of how much additional knowledge was made available to them about how to

solve problems in the planning domain. The planners in the

competition can be classified into three categories:

• Non-tunable planners. In these planning systems, the problem input consists solely of the information specified above:

initial state, goal or objective, and operators. In the competition, the planners in this class included most, but not all,

of the ones that Long and Fox [22] have called “fully automated” planners.

3

In classical planning, a domain is basically a set of planning operators.

For each domain it is possible to produce an unlimited number of randomly

generated problems by specifying initial and goal states.

4

In the 2004 International Planning Competition, which was in progress at

the time that we wrote this paper, some of the restrictions have been weakened

further. For details, see hhttp://www-rcf.usc.edu/∼skoenig/icaps/icaps04/

planningcompetition.htmli.

• Tunable planners. Although these planning systems have

usually been classified as “fully automated,” there are ways

to tune them for better performance in a given planning domain. In the 2002 competition, the planners in this class included LPG [13] and FF [18].5 For LPG, one of the inputs

was a setting to optimize its performance for speed, quality,

or something in between, and LPG was run with all three settings during the competition. For FF, there were two different

versions, both of which were entered in the competition.

• Domain-configurable planners. These are planning systems whose input includes detailed information about how

to solve problems in the relevant problem domain. Such

planners have sometimes been called “hand-tailored” planners [22], but that term is not accurate since the planning engine is domain-independent. They have also been described

as “hand-tailorable” [26] or “control-intensive” [5] planners.

In the competition, the planners of this type included SHOP2

[26], TLPlan [5], and TALplanner [19].

Performance measures for application-specific planners.

For application-specific planning systems, usually the performance measures and the ways of testing them are also

application-specific. For example, manufacturing-planning systems are tested on collections of manufacturing-planning problems that are specific to the particular domain in which the

planning is done (e.g., see [29]); and in computer bridge [31],

there are annual competitions in which performance is measured by playing the programs against each other on a set of

bridge hands, using the normal rules for a bridge tournament.

These kinds of measures are useful for the application domain

at hand, but they are not directly generalizable to other domains.

5.2. Observations

From the survey in the previous section, we can make the

following observations.

Observation 1: There is a tradeoff between the amount of

work needed to configure a planner for a domain, and planner’s speed and coverage of that domain once it has been so

configured. Here are several examples:

• In the planning competitions, the non-tunable planners were

the ones that had the highest running time and solved the

fewest planning problems—but configuring a non-tunable

planner requires no workwhatsoever, provided that the planner is capable of representing the planning domain.

• In the planning competitions, the tunable planners were

faster than the fully automated ones. However, some experimentation may be required to find the settings that give the

best overall performance.

5Some of the other planners in the competition may also be capable of being

tuned, but LPG and FF were the only ones for which results were submitted

using more than one setting or version.
• In the planning competitions, the domain-configurable planners solved planning problems several orders of magnitude

faster than the others, and solved many problems that were

too large for the other planners to solve. However, the

domain-configurable planners require a significant amount of

up-front work to formulate the domain-specific knowledge

that enables them to run so quickly, and this work must be

redone each time one switches to a new domain.

• In order to get top-level performance in a specific application

domain, it may be necessary to develop a domain-specific

planner.6 However, developing and tuning such planners may

require years of work. The resulting planning system may be

quite good for its particular application domain, but cannot

be used to solve problems in any other domain.

Observation 2: Performance in classical planning domains

does not predict performance in other planning-competition domains. For example:

• Some of the planning systems were designed, sometimes

consciously and sometimes tacitly, with classical planning

in mind. These planners did well on classical domains, but

on non-classical domains they did not perform very well (if

they could be used at all).

• On the other hand, some of the planning systems were designed, from the ground up, to work on non-classical planning domains. These systems generally performed well on

both the classical and non-classical domains.

Observation 3: Performance in planning-competition domains does not predict performance in real-world application.

For example:

• Most of the planning systems in the competition, including

both good and bad performers, would not be directly usable in real-world applications, because of restrictions on the

kinds of planning problems that they can solve.

• A planner that performed poorly in the 2002 planning competition, IxTetT [20], is used quite successfully for the application of robot motion planning [21], a domain which most

of the systems in the competition would be unable to address.

• One of the best performers in the 2002 planning competition,

SHOP2 [26], is also proving useful in several application areas. It is developing a user base that includes universities,

companies such as Sony, Lockheed Martin, and SIFT, and

government laboratories such as NIST and NRL.

From the above observations, we conclude that it is not adequate merely to measure running time and percentage of problems solved. Such figures are not meaningful unless one also

6Some examples of such systems include Bridge Baron for computer bridge

[31], the Intelligent Bending Workstation for sheet-metal bending [16], and

RAX for autonomous spacecraft control [25].

knows the class of planning problems over which such performance can be achieved, and how much the performance will be

degraded on broader classes of planning problems.

6. A PROPOSED PERFORMANCE MEASURE

In this section, we discuss three different aspects of a planning system’s performance that we believe are important to

measure: the scope of the problems that the planner can solve,

the amount and kind of control knowledge that must be given

to the planning system, and the size of the problems that the

planning system can reasonably solve.

6.1. Problem Scope

We believe that any useful measure of performance for a

planning system needs to include the scope of the problems that

the corresponding planning algorithm is capable of solving. The

set of restrictive assumptions in Section 2 can be used as a basis

for defining what this scope is. More specifically:

• Relaxing Assumption A0 (Finite Σ). An enumerable, possibly infinite set of states may be needed, for example, to

describe actions that construct or bring new objects in the

world, or to handle numerical state variables. This brings in

some theoretical issues about decidability and termination.

• Relaxing Assumption A1 (Fully Observable Σ). If we allow a static, deterministic system to be partially observable,

then the observations of Σ will not fully disambiguate which

state Σ is in. For each observation o, there may be more than

one state s such that η(s) = o. Without knowing which state

in η

−1

(o) is the current state, it is no longer possible to predict with certainty whether an action is applicable and what

state Σ will be in after each action.

• Relaxing Assumption A2 (Deterministic Σ). In a static but

nondeterministic system, each action can lead to different

possible states, so the planner may have to consider alternatives. Usually nondeterminism requires relaxing Assumption

A5 as well. A plan must encode ways for dealing with alternatives, e.g., conditional constructs of the form “do a and,

depending on its result, do either b or c”, and iterative constructs, like “do a until a given result is obtained.” Notice that

the controller has to observe the state s: here we are planning

for a closed-loop control.

If the complete knowledge assumption (Assumption A1) is

also relaxed, this leads to another difficulty: the controller

does not know exactly the current state s of the system at

run-time. A limiting case is null observability, where no observations at all can be done at run-time. This leads to a

particular case of planning for open-loop control called conformant planning.

Some ways of dealing with nondeterminism are extensions of

techniques used in classical planning (such as Graph-based

or SAT-based planning), while others are designed specifically to deal with nondeterminism, such as planning based
on Markov Decision Processes (MDPs) [7, 14] or modelchecking techniques [10, 14].

• Relaxing Assumption A3 (Static Σ). We can easily deal

with a dynamic system Σ if it is deterministic and fully observable, and if we further assume that for every state s there

is at most one contingent event e for which γ(s, e) is not

empty, and that e will necessarily occur in s. Such a system can be mapped into the restricted model: one redefines

the transition for an action a as γ(γ(s, a), e), where e is the

event that occurs in the state γ(s, a).

In the general model of possible events that may or may not

occur in a state and “compete” with actions, a dynamic system is nondeterministic from the view point of the planner

even if |γ(s, u)| ≤ 1, u being either an action or an event.

Deciding to apply action a in s does not focus the planner’s

prediction to a single state-transition. Here again, a conditional plan will be needed.

• Relaxing Assumption A4 (Restricted Goals). Controlling

a system may require more complex objectives than reaching

a given state. One would like to be able to specify to the planner an extended goal with requirements not only on the final

state but also on the states traversed, e.g., critical states to be

avoided, states that the system should go through, states it

should stay in and other constraints on its trajectories. It may

also be desirable to have utility functions to be optimized,

e.g., to model a system that must function continuously over

an indefinite period of time.

• Relaxing Assumption A5 (Sequential Plans). Here, a plan

may be a mathematical structure that can be richer than a

simple sequence of actions. As examples, one may consider

a plan to be a partially ordered set, a sequence of sets, a conditional plan that forces alternate routes depending on the

outcome and current context of execution, a “universal plan”

or a “policy” that maps states to appropriate actions, or a

deterministic or nondeterministic automaton that determines

what action to execute depending on the previous history of

execution. Relaxing Assumption A5 is often required when

other assumptions are relaxed, as we have seen in the case of

nondeterministic systems (Assumption A3) or when relaxing

Assumptions A1, A3, A4 and A6. Plans as partially ordered

sets, or as sequences of sets of actions, are more easily handled than conditional plans and policies.

• Relaxing Assumption A6 (Implicit Time). In many planning domains, action duration and concurrency have to be

taken into account. Time can also be needed for expressing temporally constrained goals and occurrence of events

with respect to an absolute time reference. However, time is

abstracted away in the state-transition model.7 This conceptual model considers actions or events as instantaneous transitions: at each clock tick, the controller synchronously reads

the observation for the current state (if needed) and applies

7Other formalisms, such as timed automata, extend state-transition systems

by incorporating an explicit representation of time.

the planned action.

• Relaxing Assumption A7 (Offline Planning). The control

problem of driving a system towards some objectives has to

be handled online with the dynamics of that system. While

a planner may not have to worry about all the details of the

actual dynamics, it cannot ignore completely how the system

will evolve. At the least, it needs to check, online, whether

a solution plan remains valid, and, if needed, to revise it or

replan. Other approaches consider planning as a process that

modifies the controller online.

For a detailed presentation of techniques for solving planning

problems with various combinations of these restrictions, see

[14].

6.2. Control Knowledge

Another important aspect of a planning system’s performance is what kind of additional control knowledge (other than

just the problem definition) will need to be given to the planning system in order for it to address practical problems. This

includes, for example, whether the planner needs such knowledge, how precise and specific to a problem the knowledge

needs to be, whether the planner needs to be fine-tuned for different planning domains, and how easily this knowledge can be

acquired and formalized. It would be quite difficult to express

this feature in precise quantified measurements, but a qualitative

assessment of this feature can be made, on the basis of a small

set of predefined classes ranging from planners that require no

control knowledge to those that require the domain author to do

some highly demanding algorithm development.

6.3. Problem Size

A third important aspect of performance is what size of

problem a planning system can reasonably solve. For this performance aspect, the traditional measures have been numeric

ones, along the lines of “this planner can solve problems of size

n in time t” for various values of n and t. This has typically

been measured by running the planner on a randomly generated

set of planning problems.

Such a performance measure has an obvious appeal, but as

we concluded in the preceding section, it also has an important

limitation: it is highly biased by theset of benchmark problems

on which the planner is tested. If a planning system can solve

“toy problems” in which the solution plans contain hundreds

or even thousands of actions, this does not necessarily say anything about how well—or even whether—the system can solve

more useful classes of planning problems.

A more useful way of measuring performance would be to

use several classes of problems, ranging in scope from toy problems to very demanding applications, and measure performance

in each class.
6. CONCLUSION

In this paper, we have described existing performance measures for automated planning algorithms, and have discussed

the limitations and biases inherent in those performance measures. We have pointed out the importance of developing a performance measure that explicitly the restrictive assumptions on

which a planning algorithm depends—and as initial step toward

such a performance measure, we have defined and discussed a

list of restrictive assumptions that are common to most automated planning systems. We believe that this list provides an

initial step toward developing a taxonomy of restrictions that

can be used to measure the scope of planning algorithms.

Based on the above considerations, we have proposed a

composite performance measure based on three factors:

• the scope of the planning algorithm: which set of restrictive

assumption are needed and which can be lifted,

• the control knowledge and tuning required for each planning

domain,

• the size of the problems that can be solve in a reasonable

amount of time in each area of its scope (i.e., for each combination of relaxed assumptions it can handle).

Several aspects of this performance measure are not yet (or not

yet fully) developed, and we hope that this paper will encourage

researchers to make the effort needed to develop them.

ACKNOWLEDGEMENT

This work was supported in part by the CNRS, France, and

in the US by AFRL contract F30602-00-2-0505 and NSF grant

IIS0412812. The opinions expressed in this paper are those of

authors and do not necessarily reflect the opinions of the funders.

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A Flexible Approach to Quantifying Various

Dimensions of Environmental Complexity

Michael L. Anderson

Institute for Advanced Computer Studies

University of Maryland

College Park, MD 20742, USA.

Tel: (301) 405-1746 Fax: (301) 314-1353

Email: anderson@cs.umd.edu

ABSTRACT— In this paper I propose a flexible method

of quantifying various dimensions of the complexity of a test

environment, including its information density, variability, volatility, inconsistency, and uncertainty. This allows one to determine

the task performance of intelligent agents as a function of

such measures, and therefore permits derivative measures of

their perturbation tolerance—that is, their ability to cope with

a complex and changing environment.

Keywords:

complexity, perturbation tolerance, standards,

testbeds

1. INTRODUCTION

There are many important and valid approaches to measuring the performance of intelligent systems: provable

optimality; typical (and worst-case) solution times; speed

and throughput, to name just a few. However, if one is

interested, as my research group is, in complex systems

operating in changing environments with time and resource

constraints—that is, environments where there may be

no optimal solution, or no time to calculate one, and

where experience may confound expectations in significant

ways, and thus where finding some way to accomplish

something is more important than finding the theoretically

best way—then such standard measures of performance

may not capture the most interesting and crucial elements

of performance.

As is well known, maintaining adequate performance in

complex and changing environments has been a perennial

stumbling-block for intelligent systems, and an ongoing

challenge to AI. A typical AI system designed for a specific

task often fails utterly when circumstances take it even

slightly outside its task specifications. Thus, the ability to

handle unexpected difficulties, even if non-optimally—that

is, the ability to muddle through difficult situations without

breaking down—seems to us an ability worth specific

study, and, if possible, implementation.

We call this general ability to cope with a complex

and changing environment “perturbation tolerance”. The

term is meant as an extension and generalization of John

McCarthy’s notion of “elaboration tolerance”—a measure

of the ease with which a reasoning agent can add and

delete axioms from its knowledge base [1]. However,

our term is more general than McCarthy’s because his

is explicitly limited to formal, symbolic systems, and an

elaboration is defined as an action taken to change such

a system [2]. But since a given intelligent agent may

well consist of more than just a formal reasoning system,

and flexibly coping with a changing world may therefore

involve altering components in addition to, or instead of,

its formal reasoner, we define a perturbation as any change,

whether in the world or in the system itself, that impacts

the performance of the agent. Performance is meant to

be construed broadly to encompass any measurable aspect

of the agent’s operation, although, as will be explained

below, we tend to favor measures for such things as average

reward and percentage task completion over such things

as reasoning speed or throughput. Perturbation tolerance,

then, is the ability of an agent to quickly recover—that is,

to re-establish desired/expected performance levels—after

a perturbation.

However, if improving perturbation tolerance is to be

among the goals for intelligent agents, it will be necessary

to quantify and measure this aspect of performance. And if

perturbation tolerance is primarily a matter of maintaining

performance in the face of various kinds of complexity

and change, then it is just such complexity and change that

should be the focus of measurement. Further, it would be

best if, instead of each lab and working group devising

their own set of standards, there were a common standard,

and preferably one that might be applied to say something

useful about current testbeds. For instance, is Phoenix [3],

[4] more or less complex than Tileworld [5]? And how

can one compare the relative complexity of two different

Tileworld runs?

To this end, I suggest a way to specify an environment

that allows for such factors as its complexity, informa-
tion density, variability, volatility and uncertainty to be

measured. From such measures I show how derivative

measures of environmentally-relative task difficulty and

degree of perturbation can be developed, and suggest some

different metrics for measuring task performance.

2. COMPARISON WITH RELATED WORK

First, as mentioned already above, it should be made clear

that while the approach defined here could be used to

build new testbeds, it can also be used to characterize the

properties of existing testbed environments in a uniform

way. Thus, what is offered here is less a blueprint for new

standard testbed implementations, and more a suggestion

for a standard way of measuring some important properties

of the testbed environments within which intelligent agents

operate. It is perhaps worth noting that the lack of a

standard way to evaluate intelligent agents has prompted

DARPA to modify their Cognitive Information Processing

Technology research initiative to include Cognitive Systems Evaluation as a focal challenge.1

One weakness of some domain specifications, from the

standpoint of evaluating perturbation tolerance, is that they

focus on controlling the characteristics and interactions of

the agents in the world, rather than on fine control of

the world itself. In MICE, for instance [6], the main goal

was “an experimental testbed that does not simulate any

specific application domain, but can instead be modified

to impose a variety of constraints on how agents act and

interact so that we can emulate the different coordination

issues that arise in various application domains.” This

strategy is, of course, perfectly sensible when it is the

coordination strategies of multi-agent systems that is under

investigation, but it provides little foundation for measures

of perturbation tolerance per se.

Another weakness of some domain specifications is the

limited number of environmental features that can be easily

isolated and measured. For instance, the Phoenix testbed

[3], [4] offers ways of building complex and dynamic

environments (in which the main task is fighting forest

fires), but does not offer a general method for measuring

the complexity and dynamicity of those environments.

Even what is perhaps the most popular and adjustable

of the standard test domains for simulated autonomous

agents, Tileworld [5], suffers somewhat from this defect.

The main task in Tileworld is to fill holes with tiles,

quickly and efficiently, while avoiding obstacles. Among

the strengths of Tileworld is its ability to easily measure the

performance trade-off between deliberation and reactivity.

Tileworld allows one to set the value of such environmental

variables as the frequency with which objects appear and

disappear, the number and distribution of objects, and the

1http://www.darpa.mil/baa/baa02-21mod6.htm

reward value for filling each hole. However, as important

as these environmental variables are, there are also other

aspects of an environment with which an intelligent agent

must cope, and against which performance should be

measured. In addition, it is not clear how to translate

the variables governing Tileworld to those governing other

environments. Finally, Tileworld tests only planning (and

plan implementation) performance. But intelligent agents

may also need to be able to perform such tasks as the

inference-based categorization or identification of objects;

the communication of accurate information about an environment; and the mapping of stable environmental features.

The current proposal, in providing a more general approach

to measuring environmental complexity, aims to lay a

foundation for measuring performance in these tasks as a

function of the complexity of the environment, and to make

cross-domain and even cross-task comparisons easier.

3. COMPLEXITY METRICS

It is proposed that the environment be modeled as an

n-dimensional grid2 with a large number of propositions

(including sets of numeric values and node activations, to

simulate the operation of perceptual NNs, sonar, etc.) that

can characterize each location, or “square”, in the grid.

Each square may be adjacent to (accessible from) one or

more other squares. Each proposition p might or might

not hold in each square s. As s comes into the perceptual

range of the agent, it “picks up” on the propositions that

characterize it (propositions consisting of numeric values

“stimulate” the appropriate perceptual systems directly;

symbolic propositions are entered directly into the agent’s

knowledge base (KB), and might be thought of as the

sort of structured representations that would typically be

delivered to an intelligent system by a complex perceptual

system like vision).3 The combination of a grid of a certain

size and shape with its characterizing propositions is called

an overlay (O).

Any given environment has many different features that

determine its complexity, independent of the task to be

performed in that environment. Specifying the environment

in the terms given above allows one to measure these

features as follows.

3.1. Basic Measures

2For a discussion of the wide applicability of this model, see the

subsection on Generality and Extensibility, below.

3

It is perhaps worth emphasizing that the only propositions relevant to

the specification are those characterizing features of the environment that

the agent would be expected to perceive or otherwise pick up. The number

of water atoms at a given location would not be a relevant proposition

unless the agent in question is capable of seeing and counting water

atoms. Note the implication that the more perceptually sophisticated the

agent, the richer its domain.
n (overlay size): the number of squares in the overlay. If

the number of squares changes during the course of an

experiment, this will naturally have to be reflected in

the measure; whether it is best to use the average size,

the final size, or some other measure may depend on

the details of the experiment. Note that to choose the

number of squares for an environment is also to choose

the spatial granularity of the environment. There can

be some hidden difficulties here, for instance in the

case where different tasks, e.g. navigating a hallway

or picking a lock, require that an agent divide space

more or less finely. It may the that in these cases, it

will be best to treat moving from one task to another

in terms of moving from a low-granularity overlay to

a high-granularity one.

ρI (information density): the average number of propositions characterizing each square.

Vo (variability): a measure of the degree of difference in

the characterizing propositions from square to square.

Vo can be calculated as the sum of the propositional

difference between each pair of squares in the overlay

divided by their geometric (minimum graph) distance:

Vo =

Xn

i,j=1

Dp(si, sj )

G(si, sj )

(1)

Where Dp(si, sj ) is the number of propositions that

hold in si but not in sj and vice-versa; G(si, sj ) is

the distance between the squares and n is the total

number of squares in the overlay.

δo (volatility): a measure of the amount of change in the

overlay as a function of time. δo can be measured in a

way similar to Vo, except that rather than measure the

propositional difference as a function of geographical

distance, we measure it as a function of temporal

distance.

δo =

X

n,t

i,j=1

Dp(si,1, si,j )

j

(2)

Where Dp(si,1, si,j ) is the number of propositions that

hold in si at time 1, but not in si at time j, and viceversa; t is the total time of the simulation, and n is

the number of squares in the overlay.

I (inconsistency): the amount of direct contradiction

between the beliefs of an agent (in its KB) and the

propositions characterizing the environment. Note this

must be a measure of the number of direct contradictions between p and ¬p, since the inconsistency of any

two sets of propositions is in general undecidable [7].4

I can be measured as the percentage of propositions

initially in the overlay that directly contradict elements

of the agent’s initial KB (e.g., 2%, 5%, 10%, 15%,

25%). In the case where δo > 0, a more accurate measure might be the average percentage of propositions,

over time, that directly contradict elements of the

initial KB. Note, however, that this measure should not

reflect the percentage of direct contradiction between

the environment over time and the KB over time. I

is meant to be a measure of one kind of difficulty an

agent might face in its environment, that it needs to

overcome (or at least manage) in order to successfully

cope with that environment. Thus, only the initial KB

should be used to determine I, for if, through the

efforts of the agent, I approaches zero as the test run

proceeds, this is a measure of the success of the agent,

and does not represent a reduction of the difficulty of

the task the agent faced.

U (uncertainty): a measure of the difficulty of perceiving

the contents of the square correctly. Uncertainty can

be understood as the ratio of the average number of

“false” propositions (pf ) in each square to the average

total number of propositions in each square.

U = pf /ρI (3)

In the case where one is building a testbed, uncertainty

requires the designer to seed the squares with false

or inapplicable propositions, or perhaps, after assigning propositions to each square, to replace a certain

number of them with their negations. In the case of

modeling an existing testbed, or where using numeric

values rather than propositions, if the percentage of

time that the system will make perceptual errors is

known, this number can be used here.

Do (overlay difference): a measure of the propositional

difference between two overlays O1 and O2. Do

can be measured as the sum of the propositional

differences between the corresponding squares of each

overlay.

Do =

Xn

i=1

(sO1,i, sO2,i) (4)

Two overlays may have precisely the same information

density, variability and volatility, and still be charac4A practical aside: work with Active Logic shows that although an

indirect contradiction may lurk undetected in the knowledge base, it may

be sufficient for many purposes to deal only with direct contradictions.

After all, a real agent has no choice but to reason only with whatever it

has been able to come up with so far, rather than with implicit but not yet

performed inferences. Active Logic systems have been developed that can

detect, quarantine, and in some cases automatically resolve contradictions

[8]–[13].
terized by different propositions; hence this measure

of overlay difference. This is useful for cases where

an agent is to be trained in one overlay, and tested in

another, and the question is how much the differences

in the test and target domains affect performance.

It is not expected that every testbed, nor every test

run, will make use of all these measures of environmental

complexity. Depending on the capabilities of the testbed,

and on what is being tested at the time, only a few of these

measures may be appropriate. Note further that, depending

on the task, some of these measures can simulate others.

For instance, even in a completely stable environment

(δo = 0), the agent can experience the equivalent of

volatility if Vo > 0, for as it traverses the environment each

square will offer different information. This difference may

not affect the agent at all if its sole task is to map the

environment, but it could make an inference-based task

more difficult in the same way that a changing environment

would. Likewise for the case where I > 0, for as the

agent encounters these contradictions, they can offer the

equivalent of change, since change can be understood in

terms of p being true at one time, and not true at another.

Naturally, determining what manner of variation affects

what tasks, and by how much, is one of the items of

empirical interest to AI scientists. Isolating these different

kinds of complexity and change can help make these

determinations more specific and accurate.

3.2. Derivative Measures

The basic measures discussed above can be combined

in various ways to construct any number of derivative

measures. One such measure of particular importance is

of the overall complexity of the environment.

C (complexity): a measure of the overall complexity of

the environment. C can be defined as the product of

all the non-zero basic measures:

C = n × ρI × Vo × δo × (I + 1) × 100U (5)

The intuition behind this compound measure of complexity

is that there are in fact many different reasons that an

environment might be difficult to cope with, all of which,

therefore, can be considered to contribute in some way

to the overall complexity of the environment itself, or

to a measure of the environment’s contribution to the

difficulty of tasks to be performed there. For instance, a

large environment is in some sense more complex than

a small one ceteris paribus, just because there is more

of it to deal with. After all, mapping or locating objects

in a large environment is likely to be harder than doing

it in a small one. Likewise, information density captures

the notion that a more intricate environment—one that

requires a greater number of propositions to describe—

will be harder to reason about or deal with than a less

intricate one. Sometimes this will mean that an intelligent

agent has more to think about in trying to act in a more

intricate environment, and sometimes this will mean it has

more to ignore; both can be difficult. The variability and

volatility of an environment expresses the intuition that

an environment that remains more or less the same from

place to place, and from time to time, is simpler than

one that does not. Inconsistency expresses the idea that an

environment that is very different from one’s expectations

will be harder to deal with than one that is not, and,

similarly, uncertainty captures the fact that if it is harder

(for whatever reason) to correctly perceive an environment,

then certainly coping with it will also be more difficult. The

overlay difference allows one to quantify the notion that

moving between different domains can be difficult (and is

likely to be more difficult as a function of the difference).

It may well turn out, after further consideration, both

that there are more factors important to the complexity of

an environment, and that each factor contributes to a measurably different degree to overall complexity (something

that might be expressed by adding various coefficients to

equation 5). Likewise, perhaps it will turn out that more

accurate expression of overall complexity results from

adding rather than multiplying all or some of the various

factors. I would welcome such future developments as

improvements of the preliminary suggestions I am offering

here. Ultimately, an evaluation of the usefulness of these

measures will require, and suggestions for improvement

will certainly result from, their attempted application in

evaluating the performance of intelligent agents in increasingly complex environments. My hope is only that they

are well-specified enough in their current form to lend

themselves to such use.

3.3. Generality and Extensibility

I have characterized the test environment in terms of a

grid of squares of a certain size and shape. Naturally, such

a characterization is most directly applicable to artificial

environments in fact composed of such a grid (“grid

worlds”). However, it should be noted that whenever it is

possible to divide a domain into parts, and characterize

(the contents of) those parts in terms of some set of

propositions, in the sense defined above, then it should

therefore be possible to characterize and measure the

complexity of that domain in the terms set forth here. We

might call such domains “grid-available”.

One obvious case of a grid-available domain is one

consisting of a mappable terrain (or space) with discrete,

localizable features. There are very many domains of

this sort, including those, like the world itself, that are

not naturally structured according to a grid, i.e. that are
continuous. It is nevertheless possible, albeit with some

abstraction, to usefully divide such a domain into spatial

parts, and characterize the features of each part in terms

of a set of propositions.

Another class of domains that are grid-available are

those that, while not strictly-speaking spatial, nevertheless

consist of individualizable information-parts. A database is

one such domain, and the World Wide Web is another. In

each case, the domain consists of individual parts (records,

pages), with specifiable contents, that may be adjacent

to (linked to, accessible from) one or more other part(s).

Depending on the needs of the experiment, an “overlay”

might be defined as an entire database or set of web-pages,

or some particular subset, as for instance the recordset

returned by a given query.

Finally, well-specified state spaces are also gridavailable domains. Each state corresponds to a “square”

in the grid, and the agent can take actions that move it

between states. The states themselves can be characterized

in terms of some set of propositions.

Examples of domains that are not grid-available include

truly continuous or holistic domains that cannot be usefully

broken into parts and/or have few or no local properties (all

properties are properties of the whole). Domains described

at the quantum level appear to be of this sort, as global

quantum properties are often not determined by local

ones, making analysis of the parts far less useful than in

classically described domains.

4. SAMPLE PERFORMANCE METRICS

In keeping with the philosophy that flexibility and

adaptability—an ability to get along even in difficult

circumstances—are among the paramount virtues of cognitive agents, we suggest that evaluating task performance

is more important than evaluating such things as reasoning

speed, throughput, or the degree of consistency in a posttest KB. Indeed, for an intelligent agent it may be that

maintaining a consistent database is in general less important than being able to deal effectively with contradictions

while continuing to operate in a dynamic environment.5

Consider, for instance, a target location task, where the

agent must traverse an environment containing 100 targets

(lost hikers, for instance) and find them all as quickly as

possible. A simple measure of performance here might be:

M =

(TP)

(tA)

(6)

5This is because, for any sufficiently complex knowledge base that was

not produced by logical rules from a database known to be consistent,

and/or to which non-entailed facts are to be added (e.g. from sensory information), it will not be possible to know whether it is consistent, nor to

use principled methods to maintain consistency [7]. Thus, contradictions

are in this sense practically inevitable.

where T is the number of targets correctly identified,6 A

is the percentage of environmental area covered at the

time the measurement is taken (this allows a measure

of M to be taken at any time in the run, e.g., when

A = 0.25, A = 0.5, A = 0.75 etc.), t is time elapsed,

and P is the percentage of task completion (percentage of

targets, out of all 100, correctly identified). Because a low

performance time is generally only desirable when task

completion is high, t is divided by P to penalize fast but

sloppy performers.

In the case where the identification of the target is

inference-based, and therefore liable to error (for instance,

the agent has to tell the difference between lost hikers, park

rangers, and large animals), tracking not just correct target

IDs (True Positives, or TP) but also False Positives (FP),

False Negatives (FN), and True Negatives (TN) will allow

one to use the following standard performance metrics:

Sensitivity =

T P

T P +F N

Specificity =

T N

T N+F P

PPV (Positive Predictive Value) =

T P

T P +F P

NPV (Negative Predictive Value) =

T N

T N+F N

Although the bare metric M, and the measures for sensitivity, specificity, PPV and NPV, give one straightforward

way to compute the performance of a given agent, and to

compare the performance of different systems, when one is

dealing with intelligent agents that can learn, it is also very

important to measure the change in performance over time,

and as a function of increased environmental complexity.

Successive M values can be compared to assess the

learning or improvement rate of the system. Likewise, successive values for the environmental complexity measures

can be used to assess the agent’s improving ability to

handle increased environmental difficulty, for instance:

Ct (avg. complexity tolerance) =

∆C

∆M

Vot (avg. variability tolerance) =

∆Vo

∆M

δot (avg. volatility tolerance) =

∆δo

∆M

Dot (avg. domain flexibility) =

∆Do

∆M

Similar metrics can of course be used for measuring

changes in sensitivity, specificity, PPV, and NPV as a

function of task complexity. These various measures taken

together can give a clear picture of the perturbation tolerance of a given cognitive agent.

Finally, because the special abilities possessed by some

intelligent agents, such as getting advice, reorganizing

one’s KB, or changing one’s conceptual categories, can

be very time-consuming, their worth depends a great deal

on the value of accuracy -vs- the need for quickness in a

given task. Thus in many cases it is sensible to introduce

6The variable T might also be calculated as correct IDs minus incorrect

IDs (TP − FP, see below).
the domain variable RV , a subjective measure of the importance of accuracy in the current task-domain. Although

the variable RV does not actually change anything about

the domain itself, it can be used to inform the agent about

the characteristics of its task. For the autonomous agent

with complex cognitive abilities, and the ability to measure

and track its own performance, RV can provide a threshold

measure as to when (and when not) to stop and ponder.

5. IMPLEMENTATION AND APPLICATION

A general test domain—PWorld—allowing for relatively

easy characterization according to the suggested standard

has been implemented as a component object model

(COM) object on Microsoft Windows. PWorld is an n×n

grid, and all elements of the world, including characterizing propositions, are stored and tracked in a database,

with which PWorld communicates using ActiveX Data

Objects (ADO). Active elements of the world—e.g. agents,

weather, and such things as plants that can wither or

grow—are implemented as separate COM objects that

can communicate directly with the world, and indirectly

with other active elements, by calling PWorld’s various

methods, such as: addProposition(), sense(), move(), and

eat().

PWorld was recently used to measure the perturbation

tolerance of an agent using a standard reinforcement

learning technique (Q-learning), and to compare it to the

perturbation tolerance of an agent using a version of Qlearning that was enhanced with simple metacognitive

monitoring and control (MCL) to create a very simple

cognitive agent. The basic idea behind Q-learning is to

try to determine which actions, taken from which states,

lead to rewards for the agent (however these are defined),

and which actions, from which states, lead to the states

from which said rewards are available, and so on. The

value of each action that could be taken in each state—its

Q-value—is a time-discounted measure of the maximum

reward available to the agent by following a path through

state space of which the action in question is a part.

The Q-learning algorithm is guaranteed, in a static

world, to eventually converge on an optimal policy [14],

[15], regardless of the initial state of the Q-learning

policy and the reward structure of the world. Moreover,

if the world changes slowly, Q-learning is guaranteed to

converge on near-optimal policies [16]. This is to say

that Q-learners are already somewhat perturbation tolerant.

However, we found that the actual performance of a Qlearner in the face of perturbation varies considerably, and,

indeed, that post-perturbation performance is negatively

correlated to the degree of perturbation (R = −0.85, p <

0.01). We further discovered that adding even a very

simple metacognitive monitoring and control (MCL) component, that monitored reward expectations and, if expectations were repeatedly violated, instructed the Q-learner

to change its policy in one of a number of ways, could

greatly improve the perturbation tolerance of a Q-learner.

The comparative performance results are summarized in

Figure 1. The results show a high degree of correlation

between the degree of the perturbation and the ratio of

MCL to non-MCL performance (R = 0.79, p < 0.01).

See [17] for details.

 0.5

 1

 1.5

 2

 2.5

 3

 3.5

 4

 4.5

 0 1 2 3 4 5 6 7 8

MCL/non-MCL post-perturbation performance

degree of perturbation

Fig. 1. Ratio of MCL/non-MCL post-perturbation performance, as a

function of the degree of perturbation. (R = 0.79, p < 0.01)

However, from the standpoint of the current paper, what

is important is the evaluation scheme in general, and our

estimate of the “degree of perturbation” in particular. For

this, the experiment must be understood in some more

detail. To establish the above results, we built a standard

Q-learner, and, starting with no policy (all Q-values=0),

placed the Q-learner in an 8x8 grid-world—the possible

states being locations in the grid—with reward r1 in square

(1,1) and reward r2 in square (8,8). The initial reward

structure [r1,r2] of the world was one of the following:

[10,-10]; [25,5]; [35,15]; [19,21]; [15,35]; [5,25]. The Qlearner was allowed to take 10,000 actions in this initial

world, which was enough in all cases to establish a very

good albeit non-optimal policy. After receiving a reward,

the Q-learner was randomly assigned to one of the nonreward-bearing squares in the grid. In turn 10,001, the

reward structure was abruptly switched to one of the

following: [25,5]; [35,15]; [19,21]7; [15,35]; [5,25], [-

10,10].

Our task-based performance measure for the Q-learner

was the ratio of actual average reward per action taken

(henceforth, per turn) to the ideal average reward per turn,

7Except when the initial structure was [19,21], in which case the postperturbation structure was [21,19]
i.e., the average reward per turn theoretically available

to a Q-learner following an optimal policy in the given

environment. To get a handle on the difficulty of each

perturbation, we first considered that the learned Q-table

can be visualized as a topographic overlay on the grid

world, where positive rewards are attractors, and negative

rewards are repulsors, and the grade of the topography (the

differences in the Q-values for each action at each location)

corresponds to the degree of attraction to a given reward.

Following the policy recommended by the Q-table is

equivalent to moving downhill as quickly as possible. For

simplicity, we can abstract considerably from this picture,

and imagine that each square of the policy-overlay contains

a proposition indicating the direction of the slope—toward

(1,1), or toward (8,8). For a given perturbation, then, we

can get one factor in the difficulty of the change, by

counting the number of squares where the propositions

characterizing the slope (as determined by an ideal policy)

have changed. Thus, for instance, to go from the ideal

abstract policy for reward structure [10,-10] (every square

says go to (1,1)) to the abstract policy for reward structure

[-10,10] (every square says go to (8,8)) involves a large

overlay difference (Do) of value 64, but going from [19,21]

to [21,19] involves essentially no overlay difference.8

Another factor in measuring the degree of perturbation

we considered for the current case was any valence change

in the rewards. A valence change makes the perturbation

greater because it makes it harder for the agent to actually

change its abstract policy (one way to think about this

might be as the mathematical equivalent of a contradiction). For instance, a negative reward that becomes positive

(V

+) is masked from the agent because the policy is

strongly biased against visiting that state. Thus, in light

of the above considerations, we devised an equation to

estimate the degree of perturbation (Dp) in each of the 22

cases:

Dp = Do/16 + 3V

+ + V− (7)

The experiment as described primarily evaluated the

perturbation tolerance of the agent in terms of its ability

to move effectively between different (abstract) overlays,

making the overlay difference the most relevant measure.

However, other aspects of the test domain can indeed be

measured according to the metrics offered here.

8

It should be noted that this is an adaptation of the meaning of overlay

and overlay difference to fit the experimental circumstances, and the

nature of the agent being tested. If we understand the task of a Q-learner

in terms of uncovering and mapping the reward-based topography of a

given region, then this is the relevant difference between two regions

that needs measuring when assessing the difficulty of moving from one

to the other. Such adaptation of shared definitions and terms to individual

circumstances is inevitable, and care must be taken in each case to

properly explain individualized uses, and to remain sensitive to the overall

goal of allowing cross-experiment comparisons.

n (overlay size) = 64. There are 64 squares in the

overlay.

ρI (information density)= 3. Three propositions characterize each square: an X value and Y value that correspond to its location, and an R value that corresponds

to the reward available there.

Vo (variability)= 0.36. The average minimum graph distance between squares in the grid is 5.5, and the

average propositional difference is just above 2 (a

square can differ by at most 3 propositions (X, Y and

R), however most of the squares differ by 2 (X and

Y, X and R, or Y and R), and a few by only 1 (X or

Y)).

δo (volatility)= 0. The overlay does not change over time.

I (inconsistency)= 0%/3%. Two values are given here,

because when the agent begins the experiment, it has

no beliefs, and there is therefore no inconsistency.

However, when it moves between the two overlays,

it has 64 beliefs about the rewards available in each

square. Two of these beliefs are in direct conflict

with the state of the world (2/64 = 0.03). Note the

agent also has a number of beliefs about what actions

to take in what circumstances to achieve maximum

reward; many of these beliefs are false in its new

circumstances. However they are not directly about the

world, and nothing that the agent can perceive about

the world directly contradicts any of these beliefs.

Therefore, these do not count toward the measure of

inconsistency.

U (uncertainty) = 0. The agent had perfect knowledge of

its environment.

6. CHALLENGES

As the suggestions I have made are just that—preliminary

suggestions meant as the starting point of a potentially long

but important investigation, there remain some significant

questions and challenges. First, and most obvious: are the

elements of the environment identified here in fact the most

important? And are the methods suggested for measuring

them appropriate? Related to this: how easy will it be in

practice to interpret a given test domain according to this

proposal? For it is clear that even in the case where a

domain is grid-available, and where it is therefore possible

to apply these metrics, it will not necessarily be easy to

do so. Although applying these metrics will be quite easy

in domains like the one described above, where the parts

and their contents are well defined, and even expressed in

terms of the defined partition, it will be much less easy

in test environments not designed along this model, for

instance video games. Thus, some attention must be paid

to developing principled, automated methods for analyzing

test domains in accordance with the suggestions outlined

here.
7. CONCLUSION

In this paper I have suggested a standard way to characterize the size, information density, variability, volatility,

inconsistency and uncertainty of a given test environment, each of which contribute to the complexity of that

environment. I have also suggested a way to measure

the difference between two different environments of the

same size. From these basic measures, I have shown how

one can construct more comprehensive measures of the

complexity of the environment, and I have given several

examples of how the metrics can be used to measure the

task performance and perturbation tolerance of cognitive

agents. Finally, I showed how some of the metrics were

applied to demonstrate that a metacognitive monitoring

and control component could enhance the perturbation

tolerance of a simple machine-learner. Although significant

challenges remain, it is hoped that the paper will prove a

useful starting point to the investigation of an important

topic.

8. ACKNOWLEDGMENTS

This paper is a revised version of [18]. The research is

supported in part by the AFOSR.

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http://www.cs.umd.edu/ anderson/papers/aaai metrics 04.pdf
Framework for the Performance Assessment of Architectural Options on 

Intelligent Distributed Applications 

Günter Haring‡, Carlos Juiz*, Christian Kurz‡, Ramon Puigjaner*, Joachim Zottl‡

‡ Department for Computer Science and Business Informatics, University of Vienna 

Lenaugasse 2/8, A-1080 Vienna, Austria 

{guenter.haring, christian.kurz, joachim.zottl}@univie.ac.at 

*Department of Mathematics and Computer Sciences, University of Balearic Islands 

Carretera de Valldemossa, km. 7.5, 07071 Palma de Mallorca, Spain 

{cjuiz, putxi}@uib.es 

ABSTRACT 

This position paper brings together the evaluation of ambient 

intelligence architectures in context-awareness systems with 

performance modeling. Thus, firstly appropriate description 

methods for distributed intelligent applications are summarized. 

Derived from the system characterization, typical software 

performance engineering techniques are based on the augmented 

description of the model regarding performance annotations. 

However, these annotations are only related with the syntactical 

view of the architecture. In the next generation of performance 

assessment tools for intelligent context-awareness systems, the 

description of the system would be capable of reasoning and 

acquiring knowledge about performance. Having an appropriate 

architectural description including performance aspects, any 

possible design options for intelligent distributed applications can 

be evaluated according to their performance impact. Therefore, we 

propose the use of an ontology with performance-related 

information - not only to evaluate the architecture off-line - but 

also building a context broker that assesses the performance during 

execution. 

KEYWORDS: performance evaluation, distributed 

software performance engineering, context-awareness, 

ambient intelligence, mobile devices 

1. INTRODUCTION AND MOTIVATION 

To be able to create architectures for intelligent distributed 

systems one has to consider the capabilities and limitations 

of the devices running the applications. One fundamental 

aspect is performance issues which have to be included into 

the decision process when choosing between different 

architectural options. Performance analysis of architecture 

options should be integrated in early life cycle stages of a 

software development process [8]. 

The term software architecture (SA) of a program 

defines the systems structure, which comprises the software 

components, their external observable behavior and the 

relationship of these components to each other [1], [3]. A 

software design method is a systematic approach for 

creating a system design. During a given design step, the 

method may provide a set of structuring criteria to help the 

designer in decomposing the system into its components [4]. 

However, non functional features of the system, e.g. 

performance, have not been considered for those software 

design methodologies. Thus, the performance modeling of 

systems is based on a certain type of conceptual 

performance formalism (e.g. queuing networks (QN) and 

their extension (EQN), stochastic timed Petri nets (SPTN) or 

stochastic process algebra (SPA)). As the size and 

complexity dramatically increase, many software 

(distributed) systems can not provide performance 

properties as required due to fundamental architecture or 

design problems. During the last years the UML (Unified 

Modeling Language) has been widely used to specify, 

construct and document the functionality of software 

systems [15]. In order to reduce the gap between functional 

models and performance evaluation, a software and 

performance community has emerged to provide 

(automatically) accessible techniques and tools to include 

performance annotations for building performance 

prediction constituting a new topic in Software and 

Performance Engineering (SPE) [9]. 

UML diagrams provide key information required for 

performance analysis so that they describe both behavior 

and resources. Therefore, sequence, activity, state chart and 

deployment annotated diagrams may be annotated to 

express some performance information in a direct or indirect 

way [19], [20], [21]. 

In typical software architectures of distributed systems 

communication between clients and servers has an 

important role. However, the growing availability of mobile 

and wireless networks and the expansion of powerful mobile 

devices define new issues for these software distributed 

systems. Thus, applications designed for mobile computing 

are expected to run in a highly heterogeneous and dynamic 
environment, due the limited computing, storage and power 

capabilities of portable devices, the large variance in the 

communication bandwidth, and maybe the crucial factor, the 

mobility itself. In that sense, other mobile topics are 

emerging, e.g. the computing ubiquity, the natural 

interaction of the systems components and their intelligence. 

However, less attention has been paid to these last 

phenomena in the performance evaluation arena because the 

traditional software architectures for distributed applications 

are difficult to translate to ad-hoc communication 

environments [18]. Our position is that performance-related 

information must be considered not only for performance 

evaluation of the actors in a changing mobile environment, 

but also in scenarios where it is possible to reason about the 

performance activity in an intelligent ambient way and even 

take actions on it. Thus, the huge amount of knowledge that 

was researched under the software performance engineering 

may walk one step beyond to this cutting edge issue. 

The remainder of the paper is organized as follows. In 

Section 2 we overview the different factors to be considered 

in the performance assessment of ambient intelligent 

applications (from now we name this approach PA-Ai). 

Section 3 of the paper summarizes related work, mainly 

giving an overview of work similar to the scope of this 

paper. The following section details the structure of the 

performance evaluation framework. Finally Section 5 

summarizes the conclusions of this paper and provides an 

outlook to future work. 

2. FACTORS TO CONSIDER IN PA-Ai 

The following factors are the main issues to consider for 

performance assessment in ambient intelligence 

applications. 

2.1 Distributed intelligent applications 

A distributed application is an application which is executed 

based on a distributed system; therefore different parts of 

the application are processed on different machines. Usually 

the functionality of the architecture is mapped on the clientserver paradigm. However, in mobile applications the client 

and server roles are not defined so specifically, some times 

devices are clients and some times they are servers. To add 

intelligence to such an application usually means that the 

system can learn from past experiences and make future 

decisions based onto this knowledge. 

One possible scenario for a distributed intelligent 

application could be a meeting coordination system for 

office or congress use (MC scenario) [5]. In that scenario a 

congress participant enters the congress area. At that 

moment his personal digital assistants (PDA) automatically 

connects to the hotel server. It recognizes the conference 

participant, accesses his previous behavioral patterns, and 

immediately sends him information which could be useful 

for him. This information might be a room map when the 

conference is entered or the session agenda depending on 

the room being entered. It may contain a renewed session 

agenda which might have been altered due to short time 

changes. Additionally a list of the participants of the 

conference or a certain session can be offered, or 

supplementary information like presentation slides can be 

transferred to the attendees’ mobile computer. The mobile 

device can also allow for communication with other 

congress members, for example with participants of the 

same session. 

A second scenario might be useful for office 

coordination (OC scenario) [6]. A project manager can 

locate the members of his team using a “People Locating 

System (PLS)”. This system is able to detect employees 

inside a companies building. When the project manager is 

scheduling a meeting the PLS is trying to locate all 

participants to be invited to be able to deliver them a 

message about the meeting schedule. Based on the 

participants behavior when receiving meeting information in 

the past according to their respective working 

circumstances, the PLS decides which type of message it 

delivers. When it finds two people together in a room with 

several others, it reasons that they are in a meeting and 

therefore decides to send them only a message notification 

to their PDA. Other members are located at their working 

place and thus are considered to be available; therefore they 

get the full text message onto their computers. Finally, two 

more members cannot be found on the company’s site. The 

system hence accesses their appointment calendars and finds 

out that one of them has a meeting with a customer and thus 

should not be disturbed, and the other one is at his dentist. 

To both of them the system sends an email detailing the 

forthcoming meeting. 

So the key difference between the traditional clientserver architecture and these last scenarios is mainly how 

the information is represented in this changing environment. 

Whereas in traditional distributed software systems the 

representation is meant for computers to process 

information, i.e. syntactic level, in the ad hoc connected 

communication systems the representation allows devices to 

process and reason about information, i.e. semantic level. 

Therefore, it is necessary to get a semantic description of the 

components in the architecture [22]. 

Context-awareness systems not only consider the 

location but also any information that can be used to 

characterize the situation of the mobile devices, e.g. the 

system capabilities, the services offered and sought, the 

activities among devices and users, and their intentions. 

2.2 Mobile Devices 

Mobile devices, for example PDA’s or Pocket PC’s, are 

essential elements in future context-aware systems. Those 

devices are characterized by limited resources. They have 
low processing power, constraints in memory capacity, 

communication bandwidth, and battery power. Hence, it is 

important to find a performance optimal architecture for 

applications using these limited devices. 

Figure 1: Device Capabilities

Concerning distributed intelligent applications we 

should at least consider five basic categories of devices 

which could be involved in performing various tasks for the 

application (see Figure 1). At the bottom of the pyramid the 

category consisting of immobile but powerful Servers, 

Workstations or PCs is located. The Notebook or Tablet PC 

on top of them is less powerful, but can be moved freely, 

only being limited by usually low battery endurance of a 

few hours. On the next higher layer PDAs provide less 

computing power, a limited user interface but stronger 

battery life up to usually about ten hours. Smartphones on 

the layer above have extended battery life, but even less 

processing capabilities and an even smaller user interface. 

On top of the pyramid are the mobile phones which can 

feature battery life of more than a week (not at heavy use), 

but offer only very limited processing power. Also the 

potential communication bandwidth and memory capacity is 

smallest on top of the pyramid and is increasing towards the 

base of it e.g. for the servers. 

2.3 Evaluation of architecture options 

Currently a number of well established software 

architectures are known, for example: (i) Web-Services are 

software components which are made useable via 

application servers. This model is also known as serviceoriented architecture (SOA). (ii) In a Client/Server 

architecture resources are concentrated in one or a small 

number of nodes. So, in this model workload and bandwidth 

capabilities are unbalanced. (iii) In Peer-to-Peer-Systems

workload and bandwidth demands will be distributed 

uniformly among the connected processors. (iv) Component 

models are based on building blocks which describe a well 

defined functionality. Such components can be accessed 

through interfaces (e.g. Corba, J2EE or .NET). (v) PushSystems are used for efficient and timely distribution of 

information to a huge number of users. (vi) In Event-BasedSystems users are notified when determined events occur. 

These architectures possess different characteristics like 

structure, degree of hierarchy or degree of coupling. When 

evaluating architecture options some of them will tend to be 

more adequate then others, but for one application there 

might be several suitable architecture options. So, given an 

application with its requirements and usage patterns a 

number of open questions arise. Is there only one adequate 

service architecture? How can several architecture options 

be assessed and qualified? Which design is the right one 

according to the given requirements and basic conditions? 

There may not exist a perfectly fitting architecture or a 

totally unsuitable one, but architectures which achieve a 

more or less suitable solution for a given problem and 

usage. A number of methods and techniques were developed 

for the evaluation of software architectures, for example: 

ATAM (Architecture Tradeoff Analysis Method, [10]), 

SAAM (Software Architecture Analysis Method, [11]), or 

ARID (Active Reviews for Intermediate Designs, [12]). 

However, for our purpose the major question is how to 

express the performance-related information in a contextawareness intelligent application. 

3. RELATED WORK 

UML diagrams that provide key information required for 

performance analysis are those that describe behaviour and 

resources together, therefore augmented sequence, activity, 

state chart and deployment annotated diagrams may express 

some performance information. A huge number of 

approaches have been proposed to derive performance 

models from software architecture specifications [2]. 

Basically, the concept can be used in an early stage of the 

software lifecycle. It uses the SPE architectural decision 

strategy. From annotated UML diagrams performance 

models are generated in the corresponding formalism (QN, 

SPN, SPA, etc.) and then they are offline evaluated through 

analytical, numerical or discrete-event simulation 

techniques. Following this procedure, [8] uses the SPE 

methodology for deriving performance models from 

software architecture specifications. In [7] a derivation of a 

QN model from SA is presented. This approach is based on 

Client/Server software performance evaluation (CLISSPE). 

In [13] an example to generate stochastic timed Petri net 

models from UML diagrams is shown. Finally [14] presents 

an example for the derivation of a performance model from 

an object-oriented design model. Due to the huge amount 

and the variety of proposals of 1.X UML performance 

extensions, new approaches are being developed for 
performance modeling built from UML/SPT profile 

(Schedulability, Performance and Time) annotation [17]. 

Some performance analysis approaches have been 

reflected into mobile software architectures from annotated 

UML diagrams [2]. However, these solutions cover the 

mobility or location-awareness aspects, referring to the 

ability of the system to recognise the mobile components 

and the services (requested/offered) of the distributed 

system but not about the context or the ambient intelligence. 

Some performance tools and UML performance annotated 

design techniques have been connected through XML/XMI 

files [16]. 

Figure 2: Intersection of PE, SE and OE areas 

Several initiatives have been taken to deal with the 

topic of a joint terminology of context-awareness systems. 

Sponsored by the W3C, the web ontology language OWL 

seems to be a de facto standard. The OWL language builds 

on XML’s ability to define customized tagging schemes and 

the flexible approach to representing data of RDF (Resource 

Description Framework). OWL is a language for defining 

and instantiating ontologies [23]. 

Figure 2 shows some of the research areas involved in 

the development of a framework to assess the performance 

of ambient intelligence applications. SE, PE and OE 

disciplines cannot provide a complete solution by 

themselves for certain topics, for example, the scope of SPE 

problems is located at the intersection between SE and PE. 

In this paper, we focus on the overlapping area between PE 

and OE and probably should be extended to all three 

disciplines. 

Thus, critical issues in context-awareness research are 

context modeling, context intelligence (reasoning and 

knowledge) and context-privacy but other non-functional 

aspects are not considered, yet, e.g. context-aware 

performance assessment. In any case, software engineering 

has moved a bit since there are also early studies to map 

OWL into UML, but the approach on SPE may be different, 

as in next section we are going to overview. 

4. STRUCTURE OF THE PERFORMANCE 

EVALUATION FRAMEWORK 

There are several issues to be considered when defining a 

framework for the performance assessment of architectural 

choices in a context-awareness system (PA-Ai) that are 

similar to traditional SPE techniques: (i) It must be decided 

about the way the intelligent system is modeled and 

therefore, how to add the performance-related information 

(and which is interesting) into the specification with the 

minimal interference; (ii) Once the performance aspects of 

the system are depicted in the model, how to transform the 

architectural options onto a performance model and finally; 

(iii) how to evaluate the performance model of every choice. 

We are going to refer to this as Offline Performance 

Evaluation to distinguish if from the Online Adaptive 

Performance Brokerage. 

4.1 Off-line Performance Evaluation 

The framework shall provide an opportunity to compare 

different alternatives for architectures based on the 

capabilities of the involved devices and communication 

infrastructure. Thus an assessment of architecture options 

with respect to performance for various alternatives is done. 

This framework gives a strategy for a performance 

evaluation for architecture options based on relative 

performance predictions. 

Figure 3: Framework Architecture

The overall architecture of the framework is depicted in 

Figure 3. The application determines the input parameters 

which are the requirements and perspective usage of the 

system. Depending on these parameters, several 

architectural options Ai may be feasible. In the next stage, 
these architectural options (based on an appropriate 

description) are transformed into a selected performance 

model which can be evaluated. This strategy does not differ 

from the traditional performance assessment for distributed 

applications although it has to consider the semantic 

representation of the information on the model. 

An ontology is an explicit formal description of 

concepts in the domain composed of classes, properties of 

each class, and restrictions on properties. Therefore, it 

expresses the set of terms, entities, objects and classes and 

the relations between them with formal definitions. The use 

of ontologies contributes to knowledge sharing and reuse 

across systems. OWL ontologies are usually placed on web 

servers as web documents, which can be referenced by other 

ontologies and downloaded by applications that use these 

ontologies. 

Our position is that performance-related information 

may be also declared through this new approach, not only 

for performance evaluation of the actors in a changing 

mobile environment, but also in scenarios where it is 

possible to reason about the performance activity in an 

intelligent ambient way and even take actions based on it. 

On the other hand, ontologies can be used to build an 

information model, as some of the UML diagrams do, which 

allows the exploration of the information space in terms of 

the items which are represented, the associations between 

the items, the properties of the items, and even the links to 

documentation which describes and defines them (i.e., the 

external justification for the existence of the item in the 

model). That is to say that the ontology and taxonomy are 

not independent of the physical items they represent, but 

may be developed / explored in tandem. Thus, an ontology 

may consider performance-related information as 

description of the architecture of a system. Moreover, OWL 

should be compatible with other commonly used Web and 

industry standards. In particular, this includes XML and 

related standards (such as XML Schema and RDF), and 

possibly UML. Therefore we may exploit the interchange 

format between OWL and performance evaluation tools in 

the same manner as SPE engines. Figure 4 shows part of a 

simple example of OWL ontology encoded in RDF/XML. 

<owl:Class rdf:ID="PDA"> 

 <rdfs:subClassOf rdf:resource="device" /> 

 ... 

</owl:Class> 

<owl:Class rdf:ID="performanceDescriptor" /> 

<owl:ObjectProperty rdf:ID="activity"> 

 <rdfs:domain rdf:resource="#device" /> 

 <rdfs:range 

rdf:resource="#performanceDescriptor" /> 

</owl:ObjectProperty> 

<owl:ObjectProperty rdf:ID="locatedIn"> 

 ... 

 <rdfs:domain 

rdf:resource="http://www.w3.org/2002/07/owl#T

hing" /> 

 <rdfs:range rdf:resource="#building" /> 

</owl:ObjectProperty> 

<owl:Class rdf:ID="demand" /> 

 <rdfs:subClassOf 

rdf:resource="performanceDescriptor" /> 

<owl:DatatypeProperty rdf:ID="demandValue"> 

 <rdfs:domain rdf:resource="#demand" /> 

 <rdfs:range rdf:resource="&xsd;float"/> 

</owl:DatatypeProperty> 

<demand rdf:ID="exp_average"> 

 <demandValue 

rdf:datatype="&xsd;float">4.500</demandvalue> 

</demand> 

Figure 4: Simple OWL performance example

We provide a simple example of a vocabulary for 

performance-related information for the location 

information and average demand requirements of PDA 

devices (some information has been deleted due to space 

limitation of the text). 

4.2 On-line Performance Assessment 

However, proposing the use of OWL as a language to 

express similar performance annotated information as other 

de facto standards may not justify the effort. In this last 

case, only the syntactical view of OWL should be exploited. 

One of the definitive features in ambient intelligence 

applications is the service discovery, i.e., functions offered 

by various mobile (e.g. mobile phones, PDAs, notebooks) 

and non-mobile devices (e.g. servers, printers, panels) that 

can be described and advertised, so that, they are soughtand-found by others. All of the current service discovery 

and capability description mechanisms (e.g. JINI, UPnP, 

JXTA, Bluetooth...) are based on ad-hoc representation 

schemes and rely heavily on standardization due to devices 

which were not necessarily designed to work together (such 

as ones built for different purposes, by different 

manufacturers, at a different time, etc.) as we experienced in 

the AKSIS project [5]. 

Being able to communicate at a high-level of abstraction 

with other devices, and reason about their 

services/functionality and performance is necessary for the 

complete evaluation of different architectural choices. 

Thus, an ontology language will be used to describe the 

characteristics of devices, the means of access to such 

devices, the policy established by the owner for the use of a 

device, and other technical constraints and requirements that 

affect incorporating a device into a ubiquitous computing 

network. The needs established for DAML-S (DARPA 

Agent Markup Language) [25] and the RDF-based schemes 
for representing information about device characteristics 

(namely, W3C's Composite Capability/Preference Profile 

(CC/PP) and WAP Forum's User Agent Profile (UAProf)) 

directly relate to this use case and the resource infrastructure 

which will support mobile applications and dynamically 

configure/negotiate ad-hoc networks. Thus, the performance 

information about resources, activities, actions, etc. in the 

context may be included as subproperties and datatypes in 

an extended vocabulary for OWL. This performance-related 

information and several simple operational rules and 

heuristic knowledge may be used for reasoning during 

execution about the performance of devices and services. 

Therefore, scenarios as OC or MC may be implemented 

through a team of context brokers. The context brokers 

would be running on stationary servers. A service discovery 

infrastructure will meet devices and servers, and the 

ontology will acquire information and reason about users, 

location, privacy and also performance. For example, in the 

OC scenario the ontology must include identifiable places in 

order to infer about location context. Reasoning about the 

spatial situation can predict performance improvements for 

example by mirroring services or automatically by disabling 

inactive device connections. To support reasoning with the 

device hardware/software descriptions, the ontology not 

only has to include profiles that would be extensions of [24] 

but also about PDAs and mobile phones to implement the 

MC scenario. Inferring about the device profiles may play 

an important role for capacity planning during context 

execution. The DAML ontology is a temporal ontology for 

expressing time-related properties. An extended OWL 

would have to consider this crucial information for 

performance prediction since it could be used to know the 

throughput of servers, the latency of a connection, the 

utilization of a device, etc. Moreover, location and temporal 

reasoning may be correlated for performance assessment 

purposes learning about inconsistencies among 

offered/required services in the scenarios. 

5. CONCLUSION AND FUTURE WORK 

This position paper tries to address the use of ontology as 

the solution to evaluate the performance of intelligent 

context-aware systems. Our preliminary study shows that 

OWL is not only a requirement for knowledge sharing in 

pervasive ambience, but also for acquiring performancerelated information and the subsequent reasoning. However, 

the first step is to show that the syntactic use of ontologies 

for performance evaluation may incorporate the same 

information as annotated modeling languages in the SPE 

area. Thus, the off-line performance evaluation of 

architectural choices would be computed from the object 

properties and datatype definitions with performance 

constraints. The interconnection between the annotations 

and the performance tools for analytical solving or discreteevent simulation would use the XMI/XML interchange 

formats. Although this work is only overviewed in this 

paper, it could represent a primary step for evaluating the 

performance of context-awareness systems. 

A more ambitious project would be the utilization of 

context brokers in order to assess performance during 

context execution. The advantage of the OWL description of 

the ambient may use the semantics to infer performance 

knowledge. Even the off-line performance evaluation relies 

on the annotated constraint values; it seems to be possible to 

get information on-line about the relationships in the context 

and to reason about them. Thus, a team of context brokers 

would implement the architecture in various aspects of 

pervasive computing, e.g. location, timing, device profiling, 

etc. and performance. 

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1

The Semantics of Ontology Alignment

Todd C. Hughes and Benjamin C. Ashpole

Lockheed Martin Advanced Technology Laboratories

Cherry Hill, NJ

{thughes, bashpole}@atl.lmco.com

ABSTRACT

Ontology alignment is a foundational problem area for semantic

interoperability. We discuss the complexity faced by automated

alignment solutions and describe an ontology-based approach for

describing and evaluating alignments.

KEYWORDS: ontology, ontology alignment, ontology

mapping, Semantic Web

1 THE CHALLENGE OF ONTOLOGY

ALIGNMENT

The vision of semantic interoperability, the fluid sharing of

services and digitalized knowledge, is often thought to

hinge on a common, formal language that machines can

somehow understand. However, protocols and data formats

such as XML tags and schemas have proven to be

inadequate solutions primarily because the burden of

meaning is still on humans, who still must learn implicit

semantics of foreign systems in order to make them work

with their native systems. Semantic Web languages like

RDF and OWL begin to ameliorate the problem by adding

explicit semantic relationships and logical constraints

between elements (i.e., classes, properties, and restrictions)

in the form of ontologies, an extension of schemas.

However, programs that read OWL documents that conform

to a particular ontology cannot understand other OWL

documents conform to a different ontology unless there is

an explicit mapping between the ontologies. Creating this

mapping is the alignment problem, and solving it is the first

step to semantic interoperability.

Alignment between ontologies is a critical challenge for

semantic interoperability. There are (n*m ) possible

individual, undirected alignments for ontology graphs of

size n and m. Optimal graph matching algorithms run in

exponential time due to the NP-complete nature of the

search space. For large ontologies with tens of thousands of

elements, purely manual alignment methods are clearly

impractical [1], and semi-automated approaches are not

suitable for real-time applications.

Semantic interoperability requires fully automated

ontology alignment approximation techniques. This cannot

be accomplished solely by lexical comparison between

element names in different ontologies, since names (like

tags) can be abbreviations, acronyms, phrases, in different

languages, misspelled, or used in unexpected, jargonspecific ways. In addition, the size, structure, and scope of

ontologies must be considered. There is no guarantee that

two ontologies in the same domain will have terms that all

precisely and completely overlap: in one ontology, an

element name might be equivalent to several—or none—in

another. Clearly, alignment techniques must be sensitive to

a number of ontology features to find corresponding

elements. [4]

A number of prototype ontology alignment

applications have been developed to meet this challenge.

However, it is difficult to assess the efficacy of these tools

because their developers each use their own alignment

formats, test data sets, and evaluation metrics. Do et al [2]

have made a notable effort to compare alignment tools using

standard metrics, but at this point in alignment research

there is still no formal, broadly used language to describe

the output of an aligner and to judge the value of one aligner

relative to another.

2 ALIGNMENT SEMANTICS

We have developed, appropriately enough, a set of

ontologies intended to capture the semantics for relevant

metrics for automated ontology operations, including

ontology alignment. These ontologies are part of an

ongoing effort to focus the ontology alignment community

on canonical set of challenge problems, research objectives,

and evaluation criteria. Here we describe some of the

classes and properties of our ontologies, which are available

on our website [1].

2.1 Alignment and Equivalence

Alignment is distinct from equivalence for at least two

fundamental reasons. First, an ontology alignment provides

only a relation between ontology elements: any particular

element alignment will depend on the alignments between

other elements. An ontology alignment is the most stable

set of element alignments, at least in the opinion of the

aligner. This leads to a second difference, namely, that

element alignments can (and often do) have degrees of

confidence associated with them. That is, the aligner cannot

say with certainty any particular alignment is true, only that

it is the most probable alignment given other alignments.

The differences suggest that current Semantic Web

terms for expressing equivalence, such as

owl:sameClassAs, owl:samePropertyAs, and

owl:sameAs are not adequate for expressing alignments.
2

These properties are intended to capture logical, not

relative, equivalence. At this time, there are no broadly

accepted semantics for describing the uncertainty of

equivalence statements made using these properties, nor is it

clear there should be.

2.2 Alignment File

These considerations have led to a different approach to

describing alignments formally. We describe an ontology

alignment in a Semantic Web document called an

AlignmentFile. An Alignment File declares instances

of the class Alignment, where each instance states that an

element from one ontology (elementA) corresponds to an

element from the other ontology (elementB) with some

probability (alignmentConfidence). An example

alignment is shown in Figure 1.

The Alignment File format easily allows for 1-n and n1 element alignments. Should they become useful in the

future, it also allows for more unusual alignments, such

alignments between a class and a property or a (group of)

instances and a class.

2.3 Alignment Evaluation File

Alignment Files deliver the output of ontology alignment

algorithms. To assess the performance of that algorithm,

one may compare the output to a document that contains the

correct (or best) element alignments for the ontologies in

question. We refer to this document using the property

trueAlignment, and we create this document by hand.

When an automated grader compares an alignment file to a

true alignment file, it delivers another document called an

AlignmentEvaluationFile.

There are two broad categories of metrics to consider

when evaluating an alignment: experiment metrics and

performance metrics. The first category concerns the

behavior of the aligner in the experiment, independent of

the true ontology alignment. Experiment metrics include

but are not limited to:

• meanGlobalCardinality : For 1:n

alignments between elements between Ontology A

and Ontology B, this property expresses the

average value for n. (Based on Do et al [2]

local/global cardinality metric.)

• sdGlobalCardinality: For 1:n alignments

between elements between Ontology A and

Ontology B, this property expresses the standard

deviation value for n. (Also based on Do et al [2]

local/global cardinality metric.)

• unalignedElements: The number of elements

in Ontology A for which no corresponding

element in Ontology B has been found.

• alignedProportion: The proportion of

elements from Ontology B that were aligned to

elements from Ontology A.

• uniqueElements: The proportion of resources

not shared (i.e, having different URIs) between

Ontology A and Ontology B.

• alignmentChallenge: The proportion of

unique elements between Ontology A and

Ontology B to the total number of elements in

Ontology A and Ontology B.

The second category of metrics concerns the

correctness of the element alignments contained in the

alignment file. A number of these metrics are derivative of

well-known metrics from the information retrieval domain.

• truePositives: The number of correct

alignments an alignment file contains.

• falsePositives: The number of incorrect a

alignments an alignment file contains.

• falseNegatives: The number of correct

alignments missed in an alignment file.

• precision : The proportion of correct

alignments among those found, (truePositives /

(truePositives + falsePositives).

• recall: The proportion of correct alignments

found (truePositives / (truePositives +

falseNegatives)).

• fMeasure: The harmonic mean of precision and

recall (2*(precision*recall)/(precision + recall)).

• alignmentPerformance : Indicates

performance given the proportion of overlapping

resources between Ontology A and Ontology B

(alignmentChallenge * fMeasure).

Figure 1. An example instance of an Alignment, shown

in the N3 language with simplified URI’s. [1] The

classes and properties are all defined in the Alignment

Ontology (referred via the ao: prefix).

:Alignment1 a ao:Alignment;

ao:elementA

<someOntologyA#ClassA>;

ao:elementB

<someOntologyB#ClassB>;

ao:alignmentConfidence "0.5".
3

All of the above performance metrics with the

exception of last one are borrowed from Do et al [4]. A

partial example of an Alignment Evaluation File is shown in

Figure 2. The metrics provide a fairly comprehensive

account of the performance of an alignment algorithm,

while the ontological framework allows the addition of new

metrics as needed.

3 CONCLUSION

The purpose of creating these ontologies is not only to

facilitate our own experimentation with alignment

algorithms, but also to facilitate greater collaboration among

members of the ontology alignment research community.

With a common representational scheme for stating and

evaluating alignments, it becomes significantly easier to

compare alignment algorithms. Of course, in addition to

this framework canonical data sets are also needed to ensure

fair and accurate comparisons.

To that end, we have made these ontologies freely

available on our website, which also includes sample data

sets and an Experiment Set Platform for administering

ontology alignment experiments. We have collaborated

with NIST to establish an ontology alignment competition

based on the model of the Text Retrieval Conference

(TREC), called the Information Interpretation and

Integration Conference (I3CON). This event will be the first

systematic comparison of ontology alignment algorithms.

Finally, it bears mentioning that ontology alignment is

not valuable for its own sake, but is worthwhile only in the

service of some other function that requires it. We envision

considerable value in automated ontology alignment

capabilities for agents that semantically interoperate with

heterogeneous (particularly legacy) data systems. As such,

the ontologies for ontology alignment should grow to

encompass semantic interoperation use cases. These new

concepts should allow us to articulate in a formal way the

impact of ontology alignment on agent mission success.

4 REFERENCES

[1] Berners-Lee, Timothy. “Getting into the Semantic

Web and RDF using N3.”

http://www.w3.org/2000/10/swap/Primer.html

[2] Do, Hong-Hai, Sergey Melnik, and Erhard Rahm.

“Comparison of Schema Matching Evaluations.”

Proceedings of the 2nd Int. Workshop on Web

Databases. German Informatics Society, 2002.

Available at:

http://citeseer.ist.psu.edu/do02comparison.html

[3] McGuinness, Deborah L., Richard Fikes, James

Rice, and Steve Wilder. "An Environment for

Merging and Testing Large Ontologies."

Proceedings of the Seventh International

Conference on Principles of Knowledge

Representation and Reasoning (KR2000).

Breckenridge, Colorado, USA. April 12-15, 2000.

Available at:

http://www.ksl.stanford.edu/software/chimaera/

[4] Rahm, Erhard, and Phillip A. Bernstein. “On

Matching Schemas Automatically.” Technical

Report for Univ. Leipzig, Dept. of Computer

Science, Database Group. 2001. Available at:

http://dol.uni-leipzig.de/pub/2001-5

[5] The Ontology Alignment Source,

http://www.atl.lmco.com/projects/ontology/

[6] Information Interpretation and Integration

Conference,

http://www.atl.lmco.com/projects/ontology/i3con.h

tml

<AlignmentEvaluation123.n3>

a ae:AlignmentEvaluationFile;

oe:evaluates

<AlignmentFile123.n3>;

ae:trueAlignment

<TrueAlignmentAB.n3>;

oe:grader <Grader1.n3>;

ae:meanGlobalCardinality "0.5";

ae:sdGlobalCardinality "0.5";

ae:unalignedElements "0.5";

ae:alignmentProportion "0.5";

ae:uniqueElements "0.5";

ae:alignmentChallenge "0.8";

ae:truePositives "0.8";

ae:falseNegatives "0.0";

ae:precision "0.8";

ae:recall "0.8";

ae:fMeasure "0.8".

ae:alignmentPerformance "0.64".

Figure 2. Partial Example Alignment Evaluation File

with Simplified URIs. Prefixes refer to the Alignment

Evaluation Ontology (ae:) and an “upper” Ontology

Operation Evaluation Ontology (oe:).
10/7/2004 LOCKHEED MARTIN 

Introducing Introducing

I

3CON

The Information Interpretation and The Information Interpretation and 

Integration Conference Integration Conference

Todd Hughes, Ph.D. Todd Hughes, Ph.D. Senior Member, Enginee

Senior Member, Enginee

Advanced Technology L

Advanced Technology L
10/7/2004 LOCKHEED MARTIN 

I

3CON: Motivation CON: Motivation

• Semantic integration will be Semantic integration will be 

one of the first major one of the first major accomplishments for accomplishments for ontology ontology

-based applications based applications

– Heterogeneous Heterogeneous 

information system and information system and resource Interoperability resource Interoperability is a major concern for is a major concern for military, government, military, government, industry industry

– Many view this as the a Many view this as the a 

fundamental technical fundamental technical challenge of the Semantic challenge of the Semantic Web 

• To answer this challe

To answer this chall

there have been new there have been new developments in aut

developments in aut

ontology and schem

ontology and schem

o Markupo Alignment Alignmento Merging Mergingo Translation Translationo Learning Learning 

• Much of this researc

Much of this researc

been funded by DAR

been funded by DAR

programs, but today 

programs, but today 

largest sponsors are 

largest sponsors are 

programs programs
10/7/2004 LOCKHEED MARTIN 

I

3CON: Observation CON: Observation

• Semantic integration Semantic integration 

research community research community resembles the text retrieval resembles the text retrieval community of 15 years ago community of 15 years ago

o Critical mass of globally Critical mass of globally 

distributed research distributed research programs programs

o Large variety of technical Large variety of technical 

approaches approaches

o Generally, but not Generally, but not 

universally, accepted universally, accepted metrics metrics

o No meaningful basis of No meaningful basis of 

evaluating one technical evaluating one technical approach over another approach over another

• The success of text r

The success of text r

technology was due i

technology was due 

measure to the Text R

measure to the Text R

Conference (TREC) Conference (TREC)

– Promoted well Promoted well

-def

de

concepts for meas

concepts for meas

success success

– Clarified metrics Clarified metrics– Established realis

Established realis

benchmarks benchmarks

– Created canonica

Created canonica

challenge problem

challenge problem

The NIST TREC mode

proven record of su

The NIST TREC mode

The NIST TREC mode

proven record of suc

proven record of suc
10/7/2004 LOCKHEED MARTIN 

NIST TREC Model NIST TREC Model

1. Define the metrics Define the metrics2. Develop experiment format for easy partici

Develop experiment format for easy partici

by researchers by researchers

3. Create development data sets and test data 

Create development data sets and test data 

publish the former publish the former

4. Distribute test data sets to experiment Distribute test data sets to experiment 

participants participants

5. Collect automatically generated results dat

Collect automatically generated results dat

6. Collate and compare results data Collate and compare results data7. Hold assessment workshop and end of cyc

Hold assessment workshop and end of cyc
10/7/2004 LOCKHEED MARTIN 

I

3CON: Timeline CON: Timeline

• March 2004: March 2004: Met with NIST, “pilot” conference as Met with NIST, “pilot” conference as PerM

special session proposed special session proposed

• March

-June 2004: June 2004: 

– Formed Organizational Committee Formed Organizational Committee

– Recruited participants Recruited participants– Created ontology alignment format Created ontology alignment format– Developed test ontology pairs Developed test ontology pairs– May 25: May 25: Gave presentation at DAML PI Meeting Gave presentation at DAML PI Meeting

• June 15 2004: June 15 2004: Released test ontology pairs Released test ontology pairs

• July 16, 2004: July 16, 2004: Collected alignment results data Collected alignment results data 

• July 16 July 16

-August 20, 2004: August 20, 2004: Compiled and analyzed resu

Compiled and analyzed resu

• August 25, 2004: August 25, 2004: I

3CON special session at CON special session at PerMIS

http://www.atl.lmco.com/projects/ontology/i3con

http://www.atl.lmco.com/projects/ontology/i3co
10/7/2004 LOCKHEED MARTIN 

I

3CON and the TREC Model CON and the TREC Model

1. Define the metrics Define the metrics2. Develop experiment format Develop experiment format 

for easy participation by for easy participation by researchers researchers

3. Create development data Create development data 

sets and test data sets; sets and test data sets; publish the former publish the former

4. Distribute test data sets to Distribute test data sets to 

experiment participants experiment participants

5. Collect automatically Collect automatically 

generated results data generated results data

6. Collate and compare Collate and compare 

results data results data

7. Hold assessment workshop Hold assessment workshop 

and end of cycle and end of cycle

→Precision, Recall, Precision, Recall, fM

fM

→Ontology Alignment Ontology Alignment 

Ontology; Experimen

Ontology; ExperimePlatform

→2 development onto

2 development onto

pairs; 8 test ontology 

pairs; 8 test ontology 

→5 participants 5 participants

→Most participants su

Most participants su

alignment data for al

alignment data for a

ontology pairs ontology pairs

→Where we are today Where we are today
10/7/2004 LOCKHEED MARTIN 

I

3CON: Experiment Results Overview CON: Experiment Results Overview

Ontology Pair vs. fMeasure

0

0.10.20.30.40.50.60.70.80.9

1

Animals Sports Computer

Science

Hotels Computer

Networks

Pets Pets (no

instances)

Ru
10/7/2004 LOCKHEED MARTIN 

I

3CON: Experiment Results Overview CON: Experiment Results Overview

Organization vs. fMeasure

0

0.10.20.30.40.50.60.70.80.9

1

ATL AT&T INRIA Karlsruhe Teknowledge
10/7/2004 LOCKHEED MARTIN 

I

3CON Experiment: Lessons Learned CON Experiment: Lessons Learned

• No single technical approach performed bes

No single technical approach performed bes

test ontology pairs test ontology pairs

• No single ontology pair was best for No single ontology pair was best for all techn

tech

approaches approaches

• All approaches performed >0.5 All approaches performed >0.5 fMeasure fMeasure on 

on 

one ontology pair one ontology pair

• All approaches performed <0.5 All approaches performed <0.5 fMeasure fMeasure on 

on 

one ontology pair one ontology pair

There is much more to be 

learned from the I3CON 

experiment data.

There is much more to be There is much more to be 

learned from the I3CON learned from the I3CON 

experiment data. experiment data.
10/7/2004 LOCKHEED MARTIN 

I

3CON: Special Thanks CON: Special Thanks

• Organizational Support Organizational Support

– Larry Reeker (NIST)

– Elena Messina (NIST) Elena Messina (NIST)

• Technology and Data Technology and Data

– Ben Ashpole (ATL) Ben Ashpole (ATL)– Liz Palmer (ATL) Liz Palmer (ATL)– Emil Macarie Macarie (ATL)

– Yun Peng Yun Peng (UMBC)– Rong Pan (UMBC) Pan (UMBC)

• Experiment Participants Experiment Participants

– Jerome Pierson (INRIA) Jerome Pierson (INRIA)– John Li ( John Li (Teknowledge Teknowledge

)

– Lewis Hart (AT&T) Lewis Hart (AT&T)– Marc Ehrig (University of (University of 

Karlsruhe Karlsruhe) 

• Guest Speakers Guest Speakers

o Bill Andersen (On

Bill Andersen (On

Works)

o Mike Pool (Inform

Mike Pool (Inform

Extraction and Tr

Extraction and Tr

o Yun Peng Yun Peng (Univer

(Unive

Maryland Baltimo

Maryland Baltimo

County) County)

o Mike Gruningner Gruningner 

(University of Ma

(University of Ma
10/7/2004 LOCKHEED MARTIN 

EON 2004 EON 2004

• Evaluation of Ontology Evaluation of Ontology

-based Tools 3rd International based Tools 3rd International 

Workshop Workshop 

– http://km.aifb.uni http://km.aifb.uni

-karlsruhe.de/ws/eon2004/ karlsruhe.de/ws/eon2004/

• Located at the 3rd Internati Located at the 3rd International Semantic Web Confer

onal Semantic Web Confer

(ISWC 2004) ISWC 2004) 

– November 8, 2004 November 8, 2004 – Hiroshima Prince Hotel, Hiroshima, Japan Hiroshima Prince Hotel, Hiroshima, Japan

• EON Ontology Alignment Experiment EON Ontology Alignment Experiment

– Provides participants with Provides participants with a complete test base of a complete test base of 

ontology pairs ontology pairs

– Test is based on one particul Test is based on one particular ontology dedicated 

ar ontology dedicated 

very narrow domain and a number of alternative o

very narrow domain and a number of alternative o

of the same domain of the same domain 

IET Proprietary

Semantic Interoperability: Case Stud

Ontology-Based Solutions

Mike Pool (mpool@iet.com)

Information Extraction and Transport, Inc.

August 25, 2004
IET Proprietary

Semantic Interoperability

z “Semantic interoperability is defined as the enablement of software s

interoperate at a level in which the exchange of information is at the level. This means each system (or object of a system) can map from conceptual model to the conceptual model of other systems, thereby that the meaning of their information is transmitted, accepted, underused across the enterprise.” –Obrst et al

z How and to what extent do ontologies facilitate 

interoperability?
IET Proprietary

AIXE: IET’s Semantic Integration Tool

z Information Extraction & Transport, Inc. (IET) is 

developing the Application Information ExchangEnvironment (AIXE), as a Phase II SBIR for the N

 allow users to quickly map new, dynamic and lega

sources to the system.

 integrate diverse data at query time to generate a 

integrated data/knowledge base for answering que
IET Proprietary

Transport

Canada

Airport 

Data

DOE Fuel 

Prices DOE Power 

Plant Data

JFAS

Data 

FAA Data

JFAST 

Data

Find all international airports with 

cargo capacity over 1000 

imperial tons with naphta fuel. Is AI_Fuel a type of naphta

Fuel?

‘IAP’, no

fuel data

Cargo in metric

tonnes ?
IET Proprietary

AIXE General Approach

z Use an ontology/logic-based foundational data s

that implements OWL markup plus other tools (translation scripts, Bayesian reasoning) for interoperability

z Simple ontology and logic-aided schema extens

that logic-naïve users can implement
IET Proprietary

AIXE General Approach

z We extend the central ontology as necessary fo

new data source (database tables, spreadsheetsstructured web pages, etc.) and then define a trascheme to wrap (or rewrap) the data sources wiand property wrappers from the central ontolog

z For each data source, we define a mapping to o

ontology on a field by field basis.
IET Proprietary

<rdf:Description rdf:about="#AFSP">

<rdfs:label>Alimo</rdfs:label><rdf:type rdf:resource="&aixeFds;#APT"/><aixeFds:locationOfObject rdf:resource="&aixeFds;#ST23"/>

<aixeFds:latitudeNumD rdf:datatype="&aixeFds;#LatLongDAFormat">41060N</aixeFds:lati

<aixeFds:longitudeNumD rdf:datatype="&aixeFds;#LatLongDAFormat">0881642W</aixeFd<aixeFds:latitudeRad rdf:datatype="&aixeFds;#LatLongRadians">0.640444</aixeFds:latitud<aixeFds:longitudeRad rdf:datatype="&aixeFds;#LatLongRadians">1.540748</aixeFds:long<aixeFds:icaoCode>ETMA</aixeFds:icaoCode>

</rdf:Description> The mapping allows us to convert the 

data into AIXE format when we need it.
IET Proprietary

Reasoning Applications

z Identifying infrastructure objects in a given areaz Identifying potential dependenciesz Analyze “what if” scenarios.z Collecting all information relevant to a particula

location, etc.
IET Proprietary

z This presentation: Consider challenges that aris

integrating disparate data

 How does the ontology and supporting inference tools ease in

disparate data and what are the limitations?

 Consider in terms of example questions that we might pose to 
IET Proprietary

z Interoperability Issues

 Identity and Glossary Control Power of Transitivity Reasoning The Space Carving Problem Up and Down the Subclass Hierarchy (Granularity, Part 1) Faceting Combining Hierarchies Format and Unit Translation Granularity, Part 2 Credibility
IET Proprietary

Identity and Glossary Control

z Example Query: Find all civilian airports selling 

type F12
IET Proprietary

CODE FLIP NATO AKA EEFC DEFINITION 

A 115 F-22 BA 

115/145 octane gasoline, leaded, MIL-L-5572F (PURPLE) 

B 100 None 

100/130 octane gasoline, leaded, MIL-L-5572F (GREEN) 

C None None B91 91/96 octane gasoline, leaded, No MIL Spec. D 80 F-12 887 

80/87 octane gasoline, leaded, MIL-L-5572F (RED) 

F None None 80NL 80 octane gasoline, unleaded, No MIL Spec. 

G None None AvGas Aviation Gasoline (AVGAS), octane unknown. 

H None None 108/135 octane gasoline, leaded, No MIL Spec

K None None 73NL 73 octane gasoline, unleaded, No MIL Spec. 

L 

100LL F18 B95,B10 0 100/130 MIL Spec, low lead, aviation gasoline (BLUE)

Suppose that other data sources use different labeling convefor fuel types, i.e., they refer to F-12 fuel with a different nameThis points to an obvious ontology application, call it glossarycontrol, the management of different labels for single objects managing the polysemy of labeling terms.
IET Proprietary

z Approaches to glossary control: (i) Reify a new object for eac

used, and use identity reasoning or (ii) attach different labels objects?

:Flip_80 (i)

a owl:Class;rdfs:subClassof LowOctaneGasoline.

:Nato_F12

a owl:Class;owl:equivalentClass Flip_80.

:AKA_887

a owl:Class;owl:equivalentClass Flip_80.

:Flip_80 

a owl:Class;rdfs:subClassof LowOnatoLabel: “Nato_F12”;akaLabel: “AKA_887”;flipLabel: “Flip_80”.

:natoLabel

a owl:AnnotationProprdfs:subPropertyOf rd
IET Proprietary

z Approach (i) to glossary control:

 Use annotation properties:

z Simply map each term to the object via ‘label’ or create subprope

that allow us to quickly distinguish different labeling sources.

 e.g., (subProperty natolabel label). This keeps our ontology lean and mean, distinguishing anno

from reasoning and representation issues.
IET Proprietary

z Challenges:

 This is a straightforward way to realize the interoperability but 

more difficult to use the data implementing that label or query uterms.

z Consider, if our data source indicates that 

(fuelTypeAvailable Airport639 AKA_887)

if “AKA_887” is just a label in our ontology, we need to replace it wit

reference to the object that it denotes, i.e., Flip_80. Similarly, “Abe directly used in queries if it’s only a label, not a direct denotatiobject.
IET Proprietary

z Approach (ii) to glossary control:

 Reify an object for each new name and then declare them as i

z This simplifies data transformation and querying.

 Challenges:

z This may complicate inferencing depending on means of support

reasoning, by dramatically increasing the size of the knowledge bto support all the identity reasoning. 

z We conflate annotation issues with representation issues in our o
IET Proprietary

Power of Transitivity and “Space Carving”

z Example Query: Find any objects in Western Pa

region dependent on objects in NERC Region, S
IET Proprietary

z Two Challenges:

 Dependency linkages Integrate the asset location and dependency information with i

about two distinct federal region breakdowns, i.e., FAA regions regions. There are many ways to subdivide the physical regiosubregions and our system must reason across each. 
IET Proprietary

Power of Transitive Reasoning

Suppose this table specifies dependencies between assets. 

We can extend the reasoning by enforcing the transitivity of dependenc

This query is more difficult in straight SQL, easy with transitive reasonin

Æ (dependentOn 5723 5066)
IET Proprietary

Space Carving

z The integration challenge arises from the need to in

asset information with different geographical inform

 (location ASSET_5066 City345) (subRegionOf City345 New Mexico) (subRegionOf New_Mexico SPP) Æ (location Asset_5066 SPP) (location ASSET_5723 City234) (subRegionOf City234 California) (subRegionOf California Western_Pac_Reg) Æ (location Asset_572

z The integration of different “space carvings” requir

 That the ontology contain the high level parts in terms of which we ca

distinct space carvings.

 The ability to represent and reason about the transitive parthood rela

B’s parts are A’s parts if B is part of A.
IET Proprietary

Up and Down the Subclass Hierarchy

z Example Query: Find all military airports in the 

northwest
IET Proprietary

z Challenge: The challenge here lies in the fact th

data sources distinguish between air force airponaval airports and other DOD-controlled airportsSimilarly, some distinguish between joint-use a(military and civilian) and military airports. Othesimply distinguish between military and civilian (Also, system needs to integrate geographical information and recognize all parts of the northw

z This is addressed rather straightforwardly, i.e., 

utilizing subtyping.
IET Proprietary

Interested users can query at the desired level of specificity. However, a more general query will also capture instances of more specific subclasses. The utilization of hierarchies overcomes some o

challenges associated with representations at different granularity levNote that the class hierarchy also allows users to quickly extend the oand map to existing schemes. And, users can do extensive querying of ignorance of the original data schemes.
IET Proprietary

Faceting

z Example Query: Find [city, airport, fuel type] mo

similar to [city, airport, fuel type] X. 
IET Proprietary

z Challenge:

 Different data schemes carve up concepts with respect to diffe

properties. Airport subtyping might be done with respect to locfunctionality, etc. Similarly, fuel typing might be done in terms chemical makeup (e.g., kerosene vs. gasoline) and/or kinds anadditives, (octane, lead, deicer).

 Answering the above question, and integrating new data into t

depends on the ability to quickly determine the different ways ireasoning space is carved up. 
IET Proprietary

z Integrating these different representational sche

requires hierarchical reasoning but also some k“faceting” or partitioning of the reasoning spaceIdeally, our integration ontology allows us to pacarve up the workspace in different ways. One second order classes:

 AirportsByFunction = {CivilAirport, MilitaryAirport, JointUseAirp AirportsBySize = {MetropolitanAirport, MidSizeAirport, 

SmallRegionalAirport, ...}
IET Proprietary

z We must recognize what the different represent

have in common, e.g., all are subclasses of airpalso allows us to focus on different ways to subthe reasoning space.

z This approach requires both multiple inheritanc

second order classes (beyond DL reasoners).

z This facilitates data retrieval and the mapping o

concepts into the domain, i.e., it becomes easiethe different ways in which the domain is partitioned/faceted. 
IET Proprietary

Combining Hierarchies

z Example Query: Find all training facilities in VA 

controlled by the DoD.
IET Proprietary

z Challenge: Relevant information is stored in up to four d

data sources, i.e., geographical information about VA, suhierarchies about military infrastructure, parthood informabout military infrastructure, and military organization ch

z Here we’re doing more than simple “isa” reasoning, we’r

reason about the extent to which properties of the whole the part, and vice versa. 

 Consider the DoD, many properties of its parts don’t apply to the who

do. We need to write more subtle rules to reason about this.

z “All things controlled by suborganizations of an organization are controlled 

organization” 

z This starts to push us further beyond simple DL-based o

this is most easily accomplished with horn rules or otherepresentation and reasoning tools beyond DLs.
IET Proprietary

Ontology Limitations

z Obviously, the more reasoning we can do the ea

to query and integrate disparate data sources, bkinds of things can’t we do with ontologies alon

 Different formats Some granularity challenges Credibility reasoning
IET Proprietary

Format and Unit Translation

z Example Query: Find all military assets between 

55 W and 30 and 40 N capable of carrying over 1metric tonnes/day.

z Challenge: One of our data sources represent lo

information in terms of radians, and most of therepresent cargo capacity in terms of imperial to

z How can an ontology help here?

 We use the ontology to track datatypes and create datatype pr

hierarchies for purposes of guiding calls to translation tools. 
IET Proprietary

Subproperty hierarchies are used to guide translation
IET Proprietary

z Parse query and remove all translatable properties

 Subquery to determine relevant “sibling” properties. (<aixeFds:latitudeDegree>,<rdf:subPropertyOf> ?X)(?PROP rdfs:sub

?PROP)

 And look for property pairs for which a translation function is defined

z SELECT ?apt ?lat ?long WHERE

 (?apt, <rdf:type>,<aixeFds:Military-Airport>)(<aixeFds:latitude> ?apt 

?lat)(aixeFds:longitude,?apt,?long)

 Note that this will return latitudeNumeric, latitudeRad and latitudeNA 

subproperties) and then we invoke appropriate translation tools. Ontrender the search reasonable.

Format and Unit Translation
IET Proprietary

Granularity, Part 2

z Example Query: Describe terrain at region3352z Example Query: Is it raining at location T?
IET Proprietary

z Challenge:

 We know the terrain in three subregions of X, how do we integ

a terrain assessment for X?

 We know weather in three different locations surrounding T, ho

approximate weather at T? 
IET Proprietary

z Here we may have to resort to other reasoning m

reason from one granularity level to another or reapply known information to the question at ha

WeatherAtA

SunnyCloudyLightRainHeavyRain

3.005.0011.081.0

WeatherAtB

SunnyCloudyLightRainHeavyRain

 0 0 0

 100

Coastal

TrueFalse

 0

 100

TimeSince

MoreThanT...OneToTwo...ThirtyToSix...TenToThirt...ZeroToMin...

PrevailingWind

HeavyTowardLightTowardNeutralHeavyAwayLightAway

 0

 100

 0 0 0

DistanceFromA

ZeroToThr...ThreeToFiv...FiveToEigh...EightToTw...GreaterTha...

 0

 100

 0 0 0

InterveningTopography

HillyForestedFlat

 100

 0 0
IET Proprietary

Credibility

z Consider other challenges:

 How do we resolve contradictory or differing reports from amo

different data sources?
IET Proprietary

z Challenge:

 Use metadata to evaluate new data sources

InformationTopic

EnergyProd ...EnergyDistri ...CyberThreatsConventiona ...

 0 0

 100

 0

U

ReliabilityScore

Reliability 4.52500

ReliabilityLevel

LowMediumHigh

5.0010.085.0

AgeOfInformation

lessThan6M ...sixToTwelve ...MoreThanT ...

 100

 0 0

LevelOfUsage

HighMediumLow

 100

 0 0

AgeOfSource

lessThan6M ...sixToTwelve ...MoreThanT ...

 0 0

 100
Ben Ashpole Ben Ashpole 

Member, Engineering St

Member, Engineering St

Advanced Technology L

Advanced Technology L

Ontology Translation Protoco

Ontology Translation Protoco

(Ontrapro) (Ontrapro)

Automated Ontology Alignment Automated Ontology Alignment
10/7/2004 

Data Description

(Schema or Ontology) (Schema or Ontology)

Data Data

Z

Y 

W V U 

A

B D

E F H

C

G

I K L M

Ontrapro Ontrapro

• Semantic integration is needed Semantic integration is needed when different informati

when different informati

systems have different formal descriptions of the same 

systems have different formal descriptions of the same 

data

• E.g., Inter E.g., Inter-agency intelligence data sharing, joint sensor agency intelligence data sharing, joint sensor 

surveillance, multinational command and control surveillance, multinational command and control

• Semantic Integration is also a Semantic Integration is also a key challenge of the Sema

key challenge of the Sem

Different descriptions Different descriptions 

(ontologies/schemas) (ontologies/schemas) 

for the same data
10/7/2004 

Data Description

(Schema or Ontology) (Schema or Ontology)

Data Data

Z

Y 

W V U 

A

B D

E F H

C

G

I K L M

Ontrapro Ontrapro

• Our approach is to develop an Our approach is to develop and/or integrate a suite of be

d/or integrate a suite of be

breed aligner algorithms breed aligner algorithms

— Ontrapro seeks to automate the process of aligning the data d

Ontrapro seeks to automate the process of aligning the data d

of fielded fielded information resources information resources

— Ontrapro discovers semantic correspondences between the e

Ontrapro discovers semantic correspondences between the e

ontologies and schemas ontologies and schemas

Ontrapro Ontrapro

A=Z

B=Y D=X

E=W F H=U

C

G

I=T K L M=V
10/7/2004 

Example: Wine Ontologies Example: Wine Ontologies

Wine

RedWine WhiteWine

RedBordeaux

CabernetMerlot CabernetMerlot

RedBurgundy

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

ItalianRed

Chablis CheninBlanc

ItialianWhite

Gewurztaminer Gewurztaminer

Chardonnay

WhiteBordeaux

Semillon

Riesling

PinotGris

Muscat

WhiteBurgundy

PinotNior PinotNior

Sake

SauvignonBlanc

Vinos

VinosRojos Vino

BurdeosRojo

MezclaDeCabernet MezclaDeCabernet

BorgonaRoja

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

RojoItaliano

Chablis 

BlancoItali

Gewurztami

Gewurztami

Chardonna

WhiteBordea

Semillon

SauvignonBl
10/7/2004 

Example: Wine Ontologies Example: Wine OntologiesTerm Dissimilarities Term Dissimilarities

Wine

RedWine WhiteWine

RedBordeaux

CabernetMerlot CabernetMerlot

RedBurgundy

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

ItalianRed

Chablis CheninBlanc

ItialianWhite

Gewurztaminer Gewurztaminer

Chardonnay

WhiteBordeaux

Semillon

Riesling

PinotGris

Muscat

WhiteBurgundy

PinotNior PinotNior

Sake

SauvignonBlanc

Vinos

VinosRojos Vino

BurdeosRojo

MezclaDeCabernet MezclaDeCabernet

BorgonaRoja

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

RojoItaliano

Chablis 

BlancoItali

Gewurztami

Gewurztami

Chardonna

WhiteBordea

Semillon

SauvignonBl
10/7/2004 

Example: Wine Ontologies Example: Wine OntologiesEdit Distance Mapping Edit Distance Mapping

Wine

RedWine WhiteWine

RedBordeaux

CabernetMerlot CabernetMerlot

RedBurgundy

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

ItalianRed

Chablis CheninBlanc

ItialianWhite

Gewurztaminer Gewurztaminer

Chardonnay

WhiteBordeaux

Semillon

Riesling

PinotGris

Muscat

WhiteBurgundy

PinotNior PinotNior

Sake

SauvignonBlanc

Vinos

VinosRojos Vino

BurdeosRojo

MezclaDeCabernet MezclaDeCabernet

BorgonaRoja

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

RojoItaliano

Chablis 

BlancoItali

Gewurztami

Gewurztami

Chardonna

WhiteBordea

Semillon

SauvignonBl
10/7/2004 

System A System A System B System B

72

9

ACB

7

3

Z

XY

Original ABSURDIST (Aligning Between Systems Usi

Original ABSURDIST (Aligning Between Systems Usi

Relations Derived Inside Systems for Translation) Relations Derived Inside Systems for Translation) 

algorithm generates a list of term correspondences 

algorithm generates a list of term correspondences 

iterating through similarity distances between system

iterating through similarity distances between system

Example: Wine Ontologies Example: Wine OntologiesStructure Mapping Structure Mapping
10/7/2004 

Example: Wine Ontologies Example: Wine OntologiesStructure Mapping Structure Mapping

Thanks to our colla

Thanks to our colla

with Indiana Univer

with Indiana Univer

now has a graph now has a graph-bas

bas

of ABSURDIST integ

of ABSURDIST integ

Ontrapro. Ontrapro.

This version of the al

This version of the al

compatible with m

compatible with m

ontology struct

ontology struct
10/7/2004 

Example: Wine Ontologies Example: Wine Ontologies...plus structure mapping ...plus structure mapping

CabernetSauvignon

Wine

RedWine WhiteWine

RedBordeaux

CabernetMerlot CabernetMerlot

RedBurgundy

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

ItalianRed

Chablis CheninBlanc

ItialianWhite

Gewurztaminer Gewurztaminer

Chardonnay

WhiteBordeaux

Semillon

Riesling

PinotGris

Muscat

WhiteBurgundy

PinotNior PinotNior

Sake

SauvignonBlanc

Vinos

VinosRojos Vino

BurdeosRojo

MezclaDeCabernet MezclaDeCabernet

BorgonaRoja

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

RojoItaliano

Chablis 

BlancoItali

Gewurztami

Gewurztami

Chardonna

WhiteBordea

Semillon

SauvignonBl
10/7/2004 

Example: Wine Ontologies Example: Wine Ontologies...plus stable marriage ...plus stable marriage

Wine

RedWine WhiteWine

RedBordeaux

CabernetMerlot CabernetMerlot

RedBurgundy

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

ItalianRed

Chablis CheninBlanc

ItialianWhite

Gewurztaminer Gewurztaminer

Chardonnay

WhiteBordeaux

Semillon

Riesling

PinotGris

Muscat

WhiteBurgundy

PinotNior PinotNior

Sake

SauvignonBlanc

Vinos

VinosRojos Vino

BurdeosRojo

MezclaDeCabernet MezclaDeCabernet

BorgonaRoja

Tempranillo

Zinfandel Zinfandel

Nebbiolo

Dolcetto

PetiteSirah

Merlot

CabernetSauvignon

Sangiovese

PinotNior PinotNior

Syrah

Chianti Chianti Berbera

RojoItaliano

Chablis 

BlancoItali

Gewurztami

Gewurztami

Chardonna

WhiteBordea

Semillon

SauvignonBl
10/7/2004 

Experiment Set Platform Experiment Set Platform

• ATL has developed a platform ATL has developed a platform 

for

— Semi-automating automating 

experiment setup experiment setup

— Automating experiment Automating experiment 

execution execution

— Automating data Automating data 

collection collection

— Used to grade alignments Used to grade alignments

• Employs a core set of Employs a core set of 

ontologies ontologies

— General Experiment General Experiment— Ontology Alignment Ontology Alignment— Alignment Evaluation Alignment Evaluation— Ontology Operation Ontology Operation— Operation Evaluation Operation Evaluation

http://cvs.sourceforge.net/viewcvs.py/ontology/ http://cvs.sourceforge.net/viewcvs.py/ontology/
10/7/2004 

Ontrapro OntraproSoftware and Tools Software and Tools 

•Developed for Developed for 

Ontrapro Ontrapro

—ABSURDIST ABSURDIST—Various aligners Various aligners 

and filters and filters

—Experiment tools Experiment tools

• E.g., AlignmentGrader AlignmentGrader, 

CombinationsRunner CombinationsRunner

—Query tools Query tools

—Integration Integration 

framework framework

•Adopted for On

Adopted for On

—Jena—Similarity Fl

Similarity Fl

—TreeJuxtapo

TreeJuxtapo

—KavaChart KavaChart—IsaViz
10/7/2004 

Ontology Alignment Sourc

Ontology Alignment Sourc

http://www.atl.external.lmco.com/projects/ontolo

http://www.atl.external.lmco.com/projects/ontolo

Copyright © 2004, Ontology Works, Inc.

Application of Formal Ontology to Database Schema Alignment - aOutline

Bill AndersenOntology Works, Inc.
Copyright © 2004, Ontology Works, Inc.

Schema alignment?

• UML-based database schemas are 

impoverished

• OWL-DL-based ontologies suffer the sa

problem

• What is needed to effect alignment of 

databases built on these formalisms?

• Depends on what we mean by alignmen

the context of federated query
Copyright © 2004, Ontology Works, Inc.

Oracle Sales DB

Id Name Dept

Employee

Does ‘Employee’ correspond to Are the employee ID numbers gthe company that owns the dataare they surrogate keys?Employees of what company? the schema.And the IDs are useless for cominformation about employees acdatabases from different compa
Copyright © 2004, Ontology Works, Inc.

Oracle Sales DB

Id Name

Product

Are products individual objects like Are product names comparable acWhat are orders?

Id Prod Qty

Order
Copyright © 2004, Ontology Works, Inc.

Oracle Sales DB

Id Name Mgr

Department

Does ‘Department’ correspond tIs an ID of a ‘Department’ like aemployee?Departments of what company? the schema.Does combining information aboDepartments across companies make sense?
Copyright © 2004, Ontology Works, Inc.

Heuristics aren’t enough

• Lexical matching of schema element na

doesn’t answer these questions 

• Structural heuristics that consider statis

significant clusters of matches don’t prothe answers either

• What could?
Copyright © 2004, Ontology Works, Inc.

Formal Ontology

• Concerned with the most general struct

of (domain-independent) reality

– Identity– Mereology– Dependence– Modality and change

• Here we can find some tools that provid

additional information needed to answequestions
Copyright © 2004, Ontology Works, Inc.

This stuff can’t be relevant, can it?

• Dependence

– Departments and employees are dependent entities 

dependent upon organizations

• Mereology

– Departments are ultimately part of organizations tha

dependent

• Identity

– Cross-DB individuation of employees and can’t com

employee IDs

• Modality

– Employeehood is a contingent matter
Copyright © 2004, Ontology Works, Inc.

Ontology-based federation

A

Schema A

B

Schema B

Domain Ontology

Formal Ontology

mappings

constraints

Formal-ontolocombined with domain contepossible mapp
Copyright © 2004, Ontology Works, Inc.

A sketch of a process

A

Schema A

Domain Ontology

Formal Ontology

Ontology A

Map Schema A elements OntologyIdentity criteria point to whinter-DB concordances arrequired Construct elaboration Ontbased on dependence relConstruct views that disaminformation in Database A
Copyright © 2004, Ontology Works, Inc.

Requirements

• Ontology language must support limited 

second-order logic (e.g., SCL)

– Full power of logic not needed once mappin

established (or else we’re in trouble)

– OWL-Full may be sufficient

• Lambda abstraction may be necessary• Suitable formal ontological content is re

(e.g., BFO, DOLCE)
Copyright © 2004, Ontology Works, Inc.

Summary

• Formal-ontological notions provide need

information to control search for mappin

– Constraints augment heuristic techniques

• Formal-ontological notions fill in missing 

information

– Improving accuracy of cross-database quer

• Formal-ontological basis provides neutr

model for integration of arbitrarily many databases

– Avoids ontological short-cuts
Copyright © 2004, Ontology Works, Inc.

Questions?
UMBC

an Honors University in Maryland

Uncertainty in Ontology Mapp

Uncertainty in Ontology Mapp

A Bayesian Perspective

Yun Peng, Zhongli Ding, Yun Peng, Zhongli Ding, Rong P

Department of Computer Science an

Electrical engineering

University of Maryland Baltimore Cou

ypeng@umbc.edu
UMBC

an Honors University in Maryland

• Motivations

– Uncertainty in ontology representation, reasoning and ma– Why Bayesian networks (BN)

• Overview of the approach• Translating OWL ontology to BN

– Representing probabilistic information in ontology– Structural translation– Constructing conditional probability tables (CPT)

• Ontology mapping

– Formalizing the notion of “mapping”– Mapping reduction– Mapping as evidential reasoning

• Conclusions

Outline
UMBC

an Honors University in Maryland

• Uncertainty in ontology engineering

– In representing/modeling the domain

• Besides A subclasOf B, also A is a small subset 

• Besides A hasProperty P, also most objects with • A and B overlap, but none is a subclass of the ot

– In reasoning

• How close a description D is to its most specific 

and most general subsumee?

• Noisy data: leads to over generalization in subsu• Uncertain input: the object is very likely an insta

class A

Motivations
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an Honors University in Maryland

– In mapping concepts from one ontology to anoth

• Similarity between concepts in two ontologies oft

be adequately represented by logical relations

– Overlap rather than inclusion

• Mappings are hardly 1-to-1

– If A in onto1 is similar to B in onto2, A would also 

the sub and super classes of B (with different degresimilarity)

• Uncertainty becomes more prevalent in web en

– One ontology may import other ontologies– Competing ontologies for the same or overlappe

Motivations
UMBC

an Honors University in Maryland

• Why Bayesian networks (BN)

– Existing approaches

• Logic based approaches are inadequate• Others often based on heuristic rules• Uncertainty is resolved during mapping, and no

considered in subsequent reasoning

– Loss of information

– BN is a graphic model of dependencies among 

• Structural similarity with OWL graph• BN semantics is compatible with that of OWL• Rich set of efficient algorithms for reasoning an

Bayesian Networks
UMBC

an Honors University in Maryland

Bayesian Networks

• Directed acyclic graph (DAG) 

– Nodes: (discrete) random variables– Arcs: causal/influential relations– A variable is independent of all other non-descend

variables, given its parents

• Conditional prob. tables (CPT)

– To each node: P(xi |πi) whereπi is the parent set 

• Chain rule:

–– Joint probability as product of CPT
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an Honors University in Maryland

Bayesian Networks
UMBC

an Honors University in Maryland

BN1

– OWL-BN translation

• By a set of translation rules and 

procedures

• Maintain OWL semantics• Ontology reasoning by probabilistic 

inference in BN

Overview of The Approach

onto1

P-onto1

Probabilistic ontological information

P-onto2

BN2

Probabilistic annotation

OWL-BN translation

concept mapping

– Ontology mapping

• A parsimonious s• Capture similarity 

by joint distributio

• Mapping as evide
UMBC

an Honors University in Maryland

• Encoding probabilities in OWL ontologies

– Not supported by current OWL– Define new classes for prior and conditional proba

• Structural translation: a set of rules

– Class hierarchy: set theoretic approach– Logical relations (equivalence, disjoint, union, inte– Properties

• Constructing CPT for each node: 

– Iterative Proportional Fitting Procedure (IPFP)

• Translated BN will preserve

– Semantics of the original ontology– Encoded probability distributions among relevant 

OWL-BN Translation
UMBC

an Honors University in Maryland

Encoding Probabilities

• Allow user to specify prior and conditional Probab

– Two new OWL classes: “PriorProbObj” and “CondProb– A probability is defined as an instance of one of these cl

• P(A): e.g., P(Animal) = 0.5

<prob:PriorProbObj rdf:ID="P(Animal)">

<prob:hasVariable><rdf:value>&ont;Animal</rdf:value></prob:h

<prob:hasProbValue>0.5</prob:hasProbValue>

</prob:PriorProbObj>

• P(A|B): e.g., P(Male|Animal) = 0.48

<prob:CondProbObjT rdf:ID="P(Male|Animal)">

<prob:hasCondition><rdf:value>&ont;Animal</rdf:value></prob

<prob:hasVariable><rdf:value>&ont;Male</rdf:value></prob:has<prob:hasProbValue>0.5</prob:hasProbValue>

</prob:CondProbObjT>
UMBC

an Honors University in Maryland

Structural Translation

• Set theoretic approach

– Each OWL class is considered a set of objects/ins

– Each class is defined as a node in BN– An arc in BN goes from a superset to a subset– Consistent with OWL semantics

<owl:Class rdf:ID=“Human">

<rdfs:subclassOf rdf:resource="#Animal"><rdfs:subclassOf rdf:resource="#Biped">

</owl:Class>

RDF Triples:(Human rdf:type owl:Class)(Human rdfs:subClassOf Animal)(Human rdfs:subClassOf Biped)

Translated to BN
UMBC

an Honors University in Maryland

Structural Translation

• Logical relations

– Some can be encoded by CPT (e.g.. Man = Human∩

– Others can be realized by 

adding control nodes

Man ⊂ Human

Woman ⊂ HumanHuman = Man ∪ Woman

Man ∩ Woman = ∅

auxiliary node: Human_1Control nodes: Disjoint, Equivalent
UMBC

an Honors University in Maryland

Constructing CPT

• Imported Probability information is not in the for• Assign initial CPT to the translated structure by s

default rules

• Iteratively modify CPT to fit imported probabiliti

setting control nodes to true.

– IPFP (Iterative Proportional Fitting Procedure)

To find Q(x) that fit Q(E1), ... Q(Ek) to the given P

• Q0(x) = P(x); then repeat Qi(x) = Qi-1(x) Q(Ej)/ Qi-1

converging

• Q∞(x) is an I-projection of P (x) on Q(E1), ... Q(Ek

(minimizing Kullback-Leibler distance to P)

– Modified IPFP for BN
UMBC

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Example
UMBC

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• Formalize the notion of mapping

• Mapping involving multiple concepts• Reasoning under ontology mapping• Assumption: ontologies have been trans

BN

Ontology Mapping
UMBC

an Honors University in Maryland

• Simplest case: Map concept E1 in Onto1 to E2 

– How similar between E1 and E2– How to impose belief (distribution) of E1 to Onto2

• Cannot do it by simple Bayesian conditioning

P(x| E1) = ΣE2 P(x| E2)P(E2 | E1) similarity(E1, E2

– Onto1 and Onto2 have different probability space (

• Q(E1) ≠ P(E1)

• New distribution, given E1 in Onto1: P*(x) ≠ΣP (x|E1)P

– similarity(E1, E2) also needs to be formalized

Formalize The Notion of Mapp
UMBC

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• Jeffrey’s rule

– Conditioning cross prob. spaces– P*(x) =ΣP (x|E1)Q(E1)

– P* is an I-projection of P (x) on Q(E1) (minimizing 

Leibler distance to P)

– Update P to P* by applying Q(E1) as soft evidence 

• similarity(E1, E2)

– Represented as joint prob. R(E1, E2) in another spa

– Can be obtained by learning or from user

• Define 

map(E1, E2) = <E1, E2, BN1, BN2, R(E1, E2)>

Formalize The Notion of Mapp
UMBC

an Honors University in Maryland

Reasoning With map(E1, E2

Q BN1

E1

P BN

E2

R 

E1 E2

Applying Q(E1) as 

soft evidence to update R to R* by 

Jeffrey’s rule

Using similarity(E1, E2):

R*(E2)

= R*(E1, E2)/R*(E1) 

Applying R

as soft evidupdate P to 

Jeffrey’s ru
UMBC

an Honors University in Maryland

Reasoning With Multiple map(E

Q BN1 P BN

R 

Multiple pair-wise mappings: map(Ak, Bk):

Realizing Jeffrey’s rule by IPFP

A1An

...

A1An

...

A1An

...

B1Bn

...
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• Multiple mappings

– One node in BN1 can map to all nodes in BN2– Most mappings with little similarity– Which of them can be removed without affecting t

• Similarity measure: 

– Jaccard-coefficient: sim(E1, E2) = P(E1 ∩ E2)/R(E1 

– A generalization of subsumption– Remove those mappings with very small sim value

• Question: can we further remove other mappin

– Utilizing knowledge in BN

Mapping Reduction
UMBC

an Honors University in Maryland

• Summary

– A principled approach to uncertainty in ont

representation, reasoning and mapping

• Current focuses: 

– OWL-BN translation: properties– Ontology mapping: mapping reduction

• Prototyping and experiments• Issues 

– Complexity– How to get these probabilities

Conclusions
Using Model-Theoretic Invaria

for Semantic Integration

Michael Gruninger

NIST /

Institute for Systems Research

University of Maryland

Michael Gruninger

NIST /

Institute for Systems Research

University of Maryland
Interoperability

Process Modeler(ProCAP / KBSI)

Simulator (Quest / Dessault)

S(I

Proce(MetC
Semantic Translation

Translation definitions specify the mappings between and application ontologies.Example: The AtomicProcess in OWL-S maps to the 

activity concept in PSL only if the activity is atomic apreconditions and effects depend only on the state prithe occurrences of the activity.(forall (?a)

(iff (AtomicProcess ?a)

(and (atomic ?a)

(markov_precond ?a)(markov_effects ?a))))
Semantic Interchange Proto
• What are sufficient conditions for an ont

to support this approach to semantic integration?

• What are sufficient conditions for an ont

to support this approach to semantic integration?
Verified Ontologies

• The meaning of t

in the ontology is characterized by models for first-ologic.

• The ontology pro

first-orderaxiomatization of class of models

• The meaning of t

in the ontology is characterized by models for first-ologic.

• The ontology pro

first-orderaxiomatization of class of models
Definitional Extensions

• Preserving semantics is equivalent to 

preserving models of the axioms.

– preserving models = isomorphism

• We classify models by using invariants

(properties of models that are preserved isomorphism).

– automorphism groups, endomorphism sem

• Classes of activities and objects are spe

using these invariants.

• Preserving semantics is equivalent to 

preserving models of the axioms.

– preserving models = isomorphism

• We classify models by using invariants

(properties of models that are preserved isomorphism).

– automorphism groups, endomorphism sem

• Classes of activities and objects are spe

using these invariants.
Models in PSL

• Occurrence trees• Fluents (state)• Activity trees• Occurrence trees• Fluents (state)• Activity trees
Twenty Questions

How can we generate translation definitio• Each invariant from the classification of 

models corresponds to a different quest

• Any particular activity or object will have 

unique value for the invariant.

• Each possible answer to a question 

corresponds to a different value for the invariant.

How can we generate translation definitio• Each invariant from the classification of 

models corresponds to a different quest

• Any particular activity or object will have 

unique value for the invariant.

• Each possible answer to a question 

corresponds to a different value for the invariant.
Limitations

• Not all theories have complete sets of 

invariants

• Invariants may not be first-order definab• How do we determine the correctness o

translation definitions?

• Not all theories have complete sets of 

invariants

• Invariants may not be first-order definab• How do we determine the correctness o

translation definitions?
Interoperability Hypothesis

• We are considering interoperability amo

complete first-order inference engines texchange first-order sentences.

• Why first-order logic?

– Soundness and completeness guarantees t

sentence is provable from a theory if and onis satisfied in all models of the theory.

• We are considering interoperability amo

complete first-order inference engines texchange first-order sentences.

• Why first-order logic?

– Soundness and completeness guarantees t

sentence is provable from a theory if and onis satisfied in all models of the theory.
Ontological Stance
Summary

• The meaning of terms in the ontology is 

characterized by models for first-order logic.

• The PSL Ontology has a first-order axiomatiza

the class of models.

• Identify invariants of the models• By axiomatizing these invariants, translation 

definitions can be shown to preserve semanticbetween software applications.

• The meaning of terms in the ontology is 

characterized by models for first-order logic.

• The PSL Ontology has a first-order axiomatiza

the class of models.

• Identify invariants of the models• By axiomatizing these invariants, translation 

definitions can be shown to preserve semanticbetween software applications.
Further Questions?

Michael Gruningergruning@nist.gov(301) 975-6536

http://www.nist.gov/psl
LOM: A Lexicon-based Ontology Mapping Tool 

John Li 

Teknowledge Corporation 

1800 Embarcadero Road 

Palo Alto, CA 94303 

ABSTRACT 

Ontology mapping is important to knowledge sharing and 

semantic integration but hard to completely automate. LOM is 

a semi-automatic lexicon-based ontology-mapping tool that 

supports a human mapping engineer with a first-cut comparison 

of ontological terms between the ontologies to be mapped, 

based on their lexical similarity. This paper will explain the 

algorithms used, the tests performed, and the applications 

developed using the results of this approach. It will also discuss 

the limitations of this approach as well as the future research 

and development issues in this field. 

KEYWORDS: ontology, mapping, lexicon, semantic 

web, semantic integration, alignment, interoperability 

1. INTRODUCTION 

 Ontology mapping is an important step to achieving 

knowledge sharing and semantic integration in an 

environment in which knowledge and information have 

been represented with different underlying ontologies. 

As more applications exploit semantic interoperability by 

employing an increasing number of ontologies developed 

by diverse communities, the demand for rapid ontology 

mapping is arising. Many efforts have been spent on 

machine-assisted ontology mapping [1]. However, this 

task is by nature very difficult to automate because 

heterogeneous ontologies may reflect fundamentally or 

subtly different perceptions of the domain by the creators 

of these ontologies. The evidence for the difficulty in 

producing a fully automated method for ontology 

mapping can be traced back to an early survey on 

automated database schemata alignment and to a recent 

one on the state of the art in ontology mapping [1, 2]. 

 We view ontology mapping as a learning process, by 

human or machine, to find a morphism between the 

concepts of the given ontologies. Given two ontologies, 

A and B, a mapping from A to B is a set of pairs (a, b)

where a is a concept expressed in A and b is its 

translation in B. Note that a and b can be represented in 

terms or expressions. Obviously the mapping is partial 

and not necessarily one-to-one depending on the 

ontologies under consideration. A good mapping tool 

should find the maximal number of potential mapping 

pairs. Naturally, if there is no overlapping of concepts in 

the two ontologies, there is no mapping that can be found 

between them. 

 As ontologies are logical theories that contain 

vocabularies and axioms for concepts, the first step in 

ontology mapping is to find the morphism between their 

vocabularies. LOM was just designed for that purpose. It 

is a prototype lexicon-based ontology-mapping tool 

developed at Teknowledge, under the Agent Semantic 

Communication Services (ASCS) project [3] for DARPA 

Agent Markup Language (DAML) Program [4]. LOM 

supports a human mapping engineer with a first-cut 

comparison of ontological terms between the ontologies 

to be mapped, based on their lexical similarity. We call 

LOM a semi-automatic method because it requires human 

validation at the end of the process. The output of LOM, 

which is a list of matched pairs of terms with scores 

ranking their similarity, will be reviewed by the human 

for the final decision. The finally approved matched 

vocabulary will serve as the basis for the axiom 

translation. 

 The development of LOM was based on the following 

two observations: (1) Human intervention in ontology 

mapping cannot be totally avoided but human labor can 

be reduced by mechanic comparisons done by intelligent 

software, and (2) The lexicon-based mapping is feasible 

because most ontologies bear lexical similarity in their 

vocabularies describing the same concepts when the 

natural languages underlying the vocabularies are the 

same (such as English). This linguistic connection exists 

naturally since most ontologies are developed by humans 

and are required to be understood by both humans and 

agents. That provides a good opportunity for our 

software to explore the common language base of the 

heterogeneous ontologies and to use syntax and semantics 

to identify the similarity between the terms. Like most 

mapping tools, LOM does not guarantee accuracy nor 

correctness in its suggested mappings. It saves human 

labor by changing their job from tedious and timeconsuming search and matching tasks to much easier ones 

of approval and validation. 

 This paper is a work-in-progress report since LOM is 

still under development. In the next section we will 

present the algorithms used in LOM (Section 2). Section 

3 describes the results of some tests as well as some 

semantic web applications using the mappings developed 
by LOM, followed by a discussion on the future 

development of LOM and possible improvements. 

Section 4 briefly reviews some related work. Section 5 

contains a summary. 

2. ALGORITHMS 

 LOM uses four methods to match the vocabularies 

from any two ontologies. They are (1) whole term 

matching; (2) word constituent matching; (3) synset 

matching; and (4) type matching. We will explain each 

method in detail below. As the first step, vocabularies 

should be separated into lists of classes, predicates and 

instances, and then compared class vs. class, predicate vs. 

predicate, etc. However, sometimes it is desirable to 

compare whole vocabularies without such classification 

since some authors may represent similar concepts with 

different types of terms. 

 LOM takes two lists of terms from ontologies A and B 

and produces a list of matched pairs. Each pair contains 

two terms: one from the source, A, and the other from the 

target, B. Each term can be multi-word, such as 

“BiologicalParent” or “office-phone-number”, etc. The 

matched pairs are then found through the following 

procedures: 

 (1) Whole term matching: This is the first as well as 

the simplest procedure to be executed. The terms in both 

ontologies are converted to lowercase and then compared 

for an exact name string match. The matched pairs are 

given a score of 1. Otherwise, the score is zero. 

 (2) Word constituent matching: This is the second 

procedure to be executed. Each term is broken into words 

wherever there is a capital letter, a hyphen or an 

underscore. Stop words such as “a”, “the”, “of”, “in”, 

etc. are dropped from multi-word terms. Remaining 

words for each term are morphologically processed and 

compared in exact string match to words of each term 

from the target ontology. Every matched pair has a score 

from 0 to 1, inclusive, representing the ratio of the 

number of the words matched with regard to the total 

number of word constituents. Then, for each term, 

among all its matched pairs, only the best-fit pairs (the 

highest scorers) are recorded and presented to the user. 

Using this procedure, unobvious matching term pairs 

such as “written-by” and “wrote”, “meeting-place” and 

“place-of-meeting” can be found. 

 (3) Synset matching: This is the third procedure to be 

executed. It explores the semantic meanings of the word 

constituents by using the WordNet [5] synsets to help 

identify synonyms in matching. A synset is a WordNet 

term for a sense or a meaning by a group of synonyms. 

This procedure is similar to the method in (2) in 

decomposing multi-word terms into their word 

constituents except that it does not perform direct 

matching between the words. For each word in each term 

in each ontology, if it is in WordNet, then it must belong 

to one of the synsets and have at least one WordNet 

synset index number. The procedure associates the 

WordNet synset index numbers of the constituent words 

with the term. The two terms which have the largest 

number of common synsets are recorded and presented to 

the user. Their score is calculated and recorded in the 

same method as that in (2). Using this procedure, the 

terms “auto-care” and “car-maintenance”, for example, 

can be matched. 

 (4) Type matching: This is the last procedure to be 

called by LOM, and it explores the ontological category 

of each word constituent for matching. It uses the 

mappings from WordNet synsets to the formal ontologies 

SUMO (the Suggested Upper Merged Ontology) [6, 7] 

and MILO (the Mid-level Ontology) [8]. SUMO and 

MILO together contain about six thousand ontological 

terms at the upper and middle level. The most popular 

WordNet synsets have been mapped into this set of terms 

[9]. LOM takes the source terms that are unmatched in 

the above-mentioned three procedures, collects the set of 

SUMO/MILO terms that their synsets map to, and then 

compares the SUMO term sets to their counterpart for 

each term in the target ontology. If there is a match, the 

matched terms are recorded and given a score based on 

the method of calculation in (2) and (3). The matched 

terms with the highest score for each term are recorded. 

Using this procedure, terms that cannot be matched by 

previous methods, either string comparison or sense 

comparison, will be matched if they represent classes or 

properties of the same type. For example, the terms 

“tank” and “armed-personal-carrier” can be matched 

since they are both military vehicles. 

 There are several caveats about the methods we 

mentioned above. First, the morphological processes 

used in procedure (2) are standard for the English 

language and we will not describe them here. However, 

if other languages are used, the morphological processes 

need to be replaced with rules for the other languages. 

Second, to do an ontology mapping from A to B, each 

term in source A is tested against every term in target B. 

Thus the algorithm runs in O(nm) time where n and m 

are the length of the two input term lists respectively. 

During the execution, the list in B does not decrease 

although that in A may, as the matched ones in the source 

may leave the game. Third, one may think the most 

efficient way to execute these four procedures is to follow 

the sequence and let each procedure process the leftover 

of the previous procedure. To determine what constitute 

the leftover, the user needs to determine the thresholds for 

all methods except (1), which has only two scores: 0 and 

1. If the score of a matching pair is below that threshold, 

the source term in the pair will be left to the next 

procedure to continue the process. Finally, after all 

methods are applied, the leftover in the source list are 
unmatched. Another way of executing these methods is 

to filter out the matched pairs after the first procedure is 

executed but leave those from the second or the third 

procedures in the game and let them do alternative 

matching. To help it, LOM identifies in its output the 

method it uses to reach the matching together with the 

score of the matching. One advantage of the second way 

of execution is that there is no need for the artificial 

thresholds. Either way, each procedure does not need to 

repeat the process done by the previous procedure, such 

as breaking-down the multi-word terms, morphologically 

processing words, and finding synsets, etc. The second 

way of execution creates more opportunities for the 

mapping but requires more time when the ontologies are 

big. Fourth, one may easily find that the precision of the 

matching differs from procedure to procedure. Obviously 

the mapping through type matching can be very 

inaccurate since there are a limited number of ontological 

categories at the upper and middle level. This method is 

used as the last resort. 

 Here we have presented an algorithm for LOM and 

explained some of its features. The whole software is 

implemented in Prolog. In the next section we will report 

some of the tests LOM underwent and some applications 

it had contributed to. We will talk more about the issues 

and possible improvements to LOM after that. 

3. TESTS AND APPLICATIONS 

3.1 Tests 

 LOM has been tested extensively in-house to evaluate 

its functionality and performance. As this paper is written, 

it is participating in a competition at I3

CON (Information 

Interpretation and Integration Conference) [10]. In its 

early development stage we had run an experiment with 

the test data created by the SENSUS development team at 

the Information Science Institute (ISI) of the University 

of Southern California [11]. The data consists of 102 

pairs of matched terms between SENSUS and CYC. 

LOM took the terms from both the SENSUS ontology 

and the CYC ontology and generated a set of mappings 

that were compared to the manual mappings that ISI and 

Cycorp created by hand. Then, metrics like precision and 

recall as used in the information retrieval were computed. 

According to our calculation, precision was 54/76 (71%) 

and recall was 54/94 (57%) for this experiment. Note 

that in this experiment we were using an early version of 

SUMO and an incomplete mapping from the WordNet 

synsets to the SUMO, so the procedures (3) and (4) did 

not help much in the mapping. Following that we did 

many test runs with the ontological terms developed by 

the DAML ontology community. The metrics generally 

improved but still varied depending on the contents and 

the representations of the ontologies to be mapped. On 

the performance measure, the time to run inputs of about 

100 terms per ontology is in seconds on a 500MHz 

laptop. The same machine with an increased RAM size 

(512MB) and an increased stack size can run inputs of 

over one thousand terms per ontology. The ability to 

perform a first-cut mapping on big ontologies has been 

the target of our performance improvement efforts 

because that ability is exactly the goal of the LOM 

development. 

3.2 Applications 

 LOM is an important component in the ASCS [4] tool 

set. ASCS was intended to provide semantic search and 

translation functions to semantic web applications. 

Teknowledge’s DAML/OWL [12] Semantic Search 

Service crawls web pages, gathers semantically marked 

contents into a repository, and provides a search engine 

that allows people to query the repository and get data as 

the answers to their queries. Its most recent version even 

allows people to publish their own data into the repository 

via URL registration, and to register their queries and get 

automatic notification when the conditions for the queries 

are met. Obviously, with such extensive and diverse 

authorship, the number of ontologies underlying the data 

is increasing steadily. Envisioning the massive growth of 

diverse ontologies, the OWL designers created a set of 

OWL terms such as “equivalentClass”, 

“equivalentProperty” and “sameAs” to help the authors of 

the ontologies to align their creation with others. Our 

semantic search engine not only can use these relations to 

seek equivalent data but also can reason with other 

ontological relating predicates such as “subClassOf”, 

“subPropertyOf” and “inverseOf” to perform semantic 

search. 

 Despite all these relating predicates and the superb 

search capability of our search engine, the semantic 

search remains a problem if the authors did not actually 

produce the equivalence instances using these predicates. 

Without these instances, the data would still be isolated 

islands. To a search engine developer, that means a query 

based on one ontology will not be able to match data 

across the ontology boundaries although they are 

semantically answerable. It can be an even severer 

problem for the semantic-search query language designers 

if they have to choose a certain ontology as the base for 

the query language because whatever ontology the query 

language is based on, the answers will stop within that 

ontology, if these instances do not exist. We took this 

opportunity to test the usability of LOM. With the help 

of LOM, we quickly located the matching pairs from a 

group of ontologies and generated a big set of 

equivalence instances over certain domains, such as 

bibliography and terrorisms. In the bibliography domain, 
for example, we mapped six ontologies to SUMO and 

generated about 300 instances of equivalent classes and 

properties in a very short time period. As expected, these 

instances greatly expanded the search range of our search 

engine and enabled it to answer queries with data marked 

in different ontologies from diverse sources. In addition, 

they enabled us to reduce our query interface to a much 

simpler one. The users do not need to remember nor 

specify the multiple terms and the multiple ontologies 

they had to use when they formed the query because there 

is only one ontology underlying the query language. With 

our recently developed Restricted English Query 

Interface [13], the user only needs to enter a conjunct 

English query (using What, Who, When, Where and other 

regular English words) and the interface will translate it 

into a logic form based on the SUMO and execute it. 

Since our repository is populated with the equivalence 

instances relating terms from other ontologies to those in 

the SUMO, our search engine will be able to gather data 

from multiple diverse sources using these relations. 

3.3 Discussion 

 Although the experiments and applications showed that 

LOM made contribution to the ontology-mapping tasks, 

we realize that there are many places where LOM can be 

improved. To strengthen the word constituent matching 

method, LOM needs to recognize proper names, 

shorthand and abbreviations correctly. For example, it 

may need to use some fuzzy syntactic analysis method to 

learn that “SemWeb” is the shorthand for 

“SemanticWeb”. As more low-level domain ontological 

terms are being developed and deployed, the mappings 

from WordNet synsets to SUMO will be updated to 

achieve higher accuracy. Both the synset matching 

method and the type matching method can benefit from 

the enhanced accuracy and find closer sense or type 

matching between the terms. As a lexicon-based 

ontology mapping method, LOM has its limitation in 

handling ontologies built with abstract symbols or codes, 

such as those used in chemistry, mathematics, or 

medicine. We plan to implement a structural mapping 

method that may alleviate the weaknesses of the lexiconbased approach by recognizing structural similarity 

between the ontologies. 

4. RELATED WORK 

Information integration has been a research topic for the 

database and KR communities for many years. With the 

emergence of the Internet and the advent of DAML/OWL 

language, semantic interoperability issues and solutions 

are gaining a greater audience. Among the vast number 

of publications related to the ontology alignment, we 

recently found the proposed conceptual alignment process 

in [14] had suggested the usage of syntactic and lexical 

analyses for similarity measuring, similar to what we have 

developed for LOM, although the development of LOM 

started in 2001, one year earlier than the proposal was 

published. Besides the difference between a proposal and 

an implementation, LOM has an additional method - type 

matching. Nevertheless, this paper provides some ideas 

about the integration of different methods that, as well as 

those in [15], might help us to explore the future 

development of LOM. Among the similarity learning 

algorithms, we found the similarity flooding algorithm 

[16] might be useful to the future development of LOM. 

Multi-strategy learning for ontology mapping was 

explored in [17]. 

5. SUMMARY 

 We have developed a lexicon-based ontology-mapping 

tool as one of many approaches in the ontology mapping 

research and development arena. This approach explores 

the lexical similarities between ontological vocabularies 

by using its four matching procedures: whole term 

matching, word constituent matching, synset matching 

and type matching. We have used it in some experiments 

and some semantic web applications in which it showed 

its strengths and weaknesses. As we view ontology 

mapping as a machine learning process, we will use this 

tool as the starting point to pursue multi-strategy learning 

of similarities between the ontologies that will take 

advantage of the strengths of various approaches. We 

expect that there will be some research and development 

issues ahead of us before all the desirable features can be 

integrated into this tool. There are vast and important 

applications (such as semantic integration, semantic web 

services) for ontology mapping in the real world. We are 

looking forward to continuing our research in this field 

and the practical deployment of our mapping tool to serve 

real-world users. 

6. ACKNOWLEDGEMENT 

 The algorithms used in LOM were designed with help 

from my former colleagues, Ian Niles and Adam Pease. I 

also wanted to thank Professor Eduard Hovy for his 

generosity in sharing his SENSUS mapping data with us 

to support our early experiment. The development of 

LOM was partially supported by the DARPA Agent 

Markup Language (DAML) program. 
7. REFERENCES 

[1] Kalfoglou, Y., and Schorlemmer, M., “Ontology 

mapping: the state of the art,” The Knowledge 

Engineering Review, Vol. 18:1, pp. 1-31, 2003. 

[2] Sheth, A. and Larson, J., “Federated database systems 

for managing distributed, heterogeneous, and autonomous 

databases,” ACM computing Surveys 22(3) pp. 183-230 

1990. 

[3] The DARPA Agent Markup Language (DAML) 

program, Internet Location: http://www.daml.org

[4] Agent Semantic Communication Services (ASCS), 

Internet Location: http://reliant.teknowledge.com/DAML/

[5] Miller, G., Beckwith, R., Fellbaum, C., Gross, D., and 

Miller, K. “Introduction to WordNet: An On-line 

Lexical Database,” International Journal of Lexicography

3(4) pp. 235-244 1990. 

[6] Niles, I., and Pease, A., “Toward a Standard Upper 

Ontology,” Proceedings of the 2nd International 

Conference on Formal Ontology in Information Systems

(FOIS-2001), Chris Welty and Barry Smith, (Eds.). 2001. 

[7] Pease, A., Niles, I., Li, J., “The Suggested Upper 

Merged Ontology: A Large Ontology for the Semantic 

Web and its Applications”, in Working Notes of the 

AAAI-2002 Workshop on Ontologies and the Semantic 

Web. 2002. 

[8] Niles, I., and Terry, A., “The MILO: A generalpurpose, mid-level ontology,” Proceedings of the 

International Conference on Information and Knowledge 

Engineering (IKE'04), Las Vegas, Nevada. 15-19. 2004. 

[9] Niles, I. and Pease, A., “Linking Lexicons and 

Ontologies: Mapping WordNet to the Suggested Upper 

Merged Ontology,” In Proceedings of the 2003 

International Conference on Information and Knowledge 

Engineering (IKE’03), Las Vegas, Nevada, June 23-26, 

2003. 

[10] Information Interpretation and Integration Conf. 

(I3

CON), August 24-26, 2004. Gaithersburg, MD., 

Internet Location: http://www.atl.external.lmco.com/ 

projects/ontology/i3con.html

[11] Hovy, E.H., “Combining and Standardizing LargeScale, Practical Ontologies for Machine Translation and 

Other Uses,” In Proceedings of the 1st International 

Conference on Language Resources and Evaluation 

(LREC). Granada, Spain. 1998. 

[12] OWL Web Ontology Language, Internet Location: 

http://www.w3.org/TR/owl-features/ 

[13] The Restricted English Query Interface, Internet 

Location: 

http://ibis.teknowledge.com:8080/DAML/query.jsp

[14] Silva, N. and Rocha, J., “Merging Ontologies using a 

Bottom-up Lexical and Structural Approach,” 

Proceedings of The Seventh International Society for 

Knowledge Organization Conference (7th ISKO), 

Granada, Spain, July 2002. 

 [15] Ehrig, M. and Sure, Y., “Ontology mapping – an 

integrated approach,” Internet Location: 

http://www.aifb.unikarlsruhe.de/WBS/meh/mapping/combinationTR.pdf

[16] Melnik, S., Garcia-Molina,H., Rahm, E., “Similarity 

Flooding: A Versatile Graph Matching Algorithm and Its 

Application to Schema Matching,” Proceedings of The 

18th International Conference on Data Engineering

(ICDE'02), San Jose, California, February 26 - March 01, 

2002. 

[17] Doan, A., Madhavan, J., Domingos, P., Halevy, A., 

“Ontology Matching: A Machine Learning Approach,” 

Handbook on Ontologies in Information Systems, S. 

Staab and R. Studer (eds.), Springer-Velag, 2004. pp. 

397-416. 
The Challenge

Of Knowledge Soup

John F. Sowa

26 August 2004 

PerMIS 2004 Workshop at NIST

Gaithersburg, Maryland

Outline of This Talk

1. Thesis: 

Support interoperability among heterogeneous systems 

by defining all concepts precisely and unambiguously. 

2. Antithesis: 

"There are more things in heaven and earth, Horatio,

Than are dreamt of in your philosophy." 

William Shakespeare

3. Synthesis: 

Develop more flexible methods of knowledge acquisition

by simulating the human cognitive cycle.

Aristotle's Syllogisms

System of logic based on four sentence patterns: 

1. Universal affirmative. Every employee is human.

2. Particular affirmative. Some employees are customers.

3. Universal negative. No employee is a competitor.

4. Particular negative. Some customers are not employees.

Affirmative patterns for stating inheritance.

Negative patterns for stating constraints.

Description logics are based on Aristotle's syllogisms.

Tree of Porphyry

Shows inheritance of differentiae from genus to species:

This diagram was translated from a version by Peter of Spain (1239).

Gottfried Wilhelm Leibniz

Encoded Aristotle's categories as integers: 

• Prime numbers to encode primitive concepts,

• Products of primes for compound concepts.

• Concept X is a subtype of Y iff Y divides X.

• The result is a lattice with multiple inheritance.

But he never realized his grand hope:

The only way to rectify our reasonings is to make them as tangible as those of

the Mathematicians, so that we can find our error at a glance, and when there

are disputes among persons, we can simply say: Let us calculate, without

further ado, in order to see who is right.

Immanuel Kant

Proposed twelve categories as a replacement for Aristotle's: 

Quantity Quality Relation Modality

Unity Reality Inherence Possibility

Plurality Negation Causality Existence

Totality Limitation Community Necessity

But he never realized his grand hope:

If one has the original and primitive concepts, it is easy to add the derivative

and subsidiary, and thus give a complete picture of the family tree of the pure

understanding. Since at present, I am concerned not with the completeness of

the system, but only with the principles to be followed, I leave this

supplementary work for another occasion.

Académie Française

Primary mission: 

• Défense de la langue française.

Strategy:

• Create a dictionary that freezes the meaning of every French word.

Result: 

• Uncontrollable growth of slang terms that never appear in the dictionary. 

• Wholesale borrowing of new words from English.

Conceptual Schema

ANSI SPARC, 1978.

ISO Standards Project, R.I.P. 1999.

Born again as the Semantic Web. 

World's Largest Ontology Project

Cyc project started in 1984 by Doug Lenat.

• Name comes from the stressed syllable of encyclopedia. 

• Goal: implement the commonsense knowledge of an average human being.

• After $70 million and 700 person-years of work,

600,000 categories

defined by 2,000,000 axioms

organized in 6,000 microtheories.

Project Halo

Project for evaluating methods of knowledge representation.

Goal: Build an intelligent tutor.

Test case: Encode knowledge from a chemistry textbook in order to answer questions

on a freshman chemistry exam.

Participants: Cycorp, OntoPrise, SRI International.

Results: 

• Average score: about 40% to 47% correct.

• Cost to encode knowledge: average about $10,000 per page from the textbook.

• Despite its large knowledge base, Cyc had the lowest score.

Utterance by a 3-year-old Child

When I was a little girl, I could go "geek, geek" like that; 

but now I can go "This is a chair."

Enormous logical complexity in one short passage:

• Subordinate and coordinate clauses

• Tenses: Earlier time contrasted with "now"

• Modal auxiliaries: can and could

• Quotations: "geek, geek" and "This is a chair"

• Metalanguage about her own linguistic abilities

• Contrast shown by but

• Parallel stylistic structure

Observations

The child has much less technical knowledge than Cyc.

But her learning ability is far more flexible and far more efficient: 

Only three person-years of effort.

No need for knowledge encoding at $10,000 per page.

Can our computer systems ever be as flexible?

Limitations of Current Approaches

The technologies of the Semantic Web (XML, RDF, and OWL) are useful for many

applications, but there is nothing new:

• They're bracketed on the low end by Aristotle's syllogisms and on the high end by

Cyc.

The cost of $10,000 to encode one page from a textbook is a major barrier to widespread

use.

In recent years, the Cyc knowledge base has expanded from 100,000 axioms to

2,000,000 axioms — but the cost of adding new knowledge has not gone down.

There's no evidence that an expansion from two million to two billion would make much,

if any difference.

The Challenge

The fluid, loosely organized, dynamically changing

contents of the human mind.

Examples of Knowledge Soup

• Overgeneralizations: Birds fly.

But what about penguins? A day-old chick? A bird with a broken wing? A

stuffed bird? A sleeping bird? A bird in a cage?

• Abnormal conditions: If you have a car, you can drive from New York to Boston. 

But what if the battery is dead? Your license has expired? There is a major

snowstorm?

• Incomplete definitions: An oil well is a hole drilled in the ground that produces oil.

But what about a dry hole? A hole that has been capped? A hole that used

to produce oil? Are three holes linked to a single pipe one oil well or

three?

• Conflicting defaults: Quakers are pacifists, and Republicans are not.

But what about Richard Nixon, who was both a Quaker and a Republican?

Was he or was he not a pacifist?

• Unanticipated applications: The parts of the human body are described in anatomy

books.

But is hair a part of the body? Hair implants? A wig? A wig made from a

person's own hair? A hair in a braid that has broken off from its root?

Fingernails? Plastic fingernail extender? A skin graft? Artificial skin

used for emergency patches? A band-aid? A bone implant? An artificial

implant in a bone? A heart transplant? An artificial heart? An artificial

leg? Teeth? Fillings in the teeth? A porcelain crown? False teeth?

Braces? A corneal transplant? Contact lenses? Eyeglasses? A tattoo?

Make-up? Clothes?

Devil in the Details

Most banks offer similar services with similar terminology:

• Checking, savings, loans, mortgages...

Banks interoperate on electronic funds transfer.

But when two banks merge, they never merge their databases.

Two common strategies: 

• Keep running both databases indefinitely, or 

• Close some or all accounts of one bank, and

open new accounts in the database of the other bank.

There are too many incompletely documented details.

Limits of Definability

• Immanuel Kant:

Since the synthesis of empirical concepts is not arbitrary but based on

experience, and as such can never be complete (for in experience ever

new characteristics of the concept can be discovered), empirical concepts

cannot be defined.

Thus only arbitrarily made concepts can be defined synthetically. Such

definitions... could also be called declarations, since in them one declares

one's thoughts or renders account of what one understands by a word.

This is the case with mathematicians.

• Wittgenstein's family resemblance:

Empirical concepts cannot be defined by a fixed set of necessary and

sufficient conditions. Instead, they can only be taught by giving a series of

examples and saying "These things and everything that resembles them

are instances of the concept."

• Waismann's open texture:

For any proposed definition of empirical concepts, new instances will

arise that "obviously" belong to the category but are excluded by the

definition.

Limits of Logic

Alfred North Whitehead, Modes of Thought:

• "Both in science and in logic, you have only to develop your argument sufficiently,

and sooner or later you are bound to arrive at a contradiction, either internally

within the argument, or externally in its reference to fact."

• "The topic of every science is an abstraction from the full concrete happenings of

nature. But every abstraction neglects the influx of the factors omitted into the

factors retained."

• "The premises are conceived in the simplicity of their individual isolation. But there

can be no logical test for the possibility that deductive procedure, leading to the

elaboration of compositions, may introduce into relevance considerations from

which the primitive notions of the topic have been abstracted."

Summary: "We must be systematic, but we should keep our systems open."

Evolution of Cognition

Every organism retains the capabilities of all earlier forms.

Peirce's Classification of Reasoning

Three methods of logic plus analogy:

1. Deduction: Deriving implications from premises.

2. Induction: Deriving general principles from examples.

3. Abduction: Forming a hypothesis that must be tested by induction and deduction.

4. Analogy: "Besides these three types of reasoning there is a fourth, analogy, which

combines the characters of the three, yet cannot be adequately represented as

composite."

Analogy is more primitive, but more flexible than logic.

The methods of logic are disciplined ways of using analogy.

Peirce's Cycle of Cognition

A Continuum of Reasoning Processes

Peirce's cycle characterizes reasoning processes at every level of difficulty and for time

periods of any length:

• Real-time operations, as described by Boyd's OODA

loop (Observe, Orient, Decide, Act), may happen in

seconds or milliseconds.

• Problem-solving cycles may take minutes to days. 

• Scientific research may take months to decades.

The central feature of Peirce's pragmatism is the grounding

of the reasoning process in perception at one end and action

at the other.

Cyc's Piece of the Pie

• Cyc does not automate Sherlock Holmes.

• It requires people like him to write axioms.

• At a cost of $10,000 to encode one page from a textbook.

Deduction is only 25% of the Cycle

The Challenge of Knowledge Soup

• Computer systems are better at

deduction than most people.

• But the greatest challenges and

opportunities are on the other side.

• How is new knowledge added to the

soup? 

• How is structured knowledge derived

from the unstructured soup?

• How is relevant knowledge found and

used when needed?

• And how can those processes be

automated? 

Ibn Taymiyya Contra Aristotle

• Fourteenth-century Islamic legal scholar.

• Admitted that deduction is necessary for pure mathematics.

• But for reasoning about the world, deduction is limited to the accuracy of the

induction.

• Given the same data, analogy can replace induction + deduction.

Ibn Taymiyya's Argument

• A theory can be very useful when available,

as in mathematics, science, and engineering.

• But analogy can be used when no theory exists,

as in law, medicine, business, and everyday life.

Structure Mapping

Mapping one conceptual structure to another can have four logical effects:

1. Equivalence: CS1≡ CS2

2. Generalization: CS1implies CS2

3. Specialization: CS2implies CS1

4. Similarity: Neither one implies the other.

Analogy uses all four.

Logic uses only the first three.

The same mechanisms, both computational and neurophysiological, underlie both.

VivoMind Analogy Engine

Structure-mapping methods used in analogy:

1. Matching labels:

• Compare type labels on conceptual graphs.

2. Matching subgraphs:

• Compare subgraphs independent of labels.

3. Matching transformations:

• Transform subgraphs.

Methods #1 and #2 take (N log N) time.

Method #3 takes polynomial time (analogies of analogies).

Using VAE for Knowledge Fusion

Challenge:

• A large corporation needed to analyze and re-engineer mainframe software and

documentation dating back to 1962.

• Extract and combine knowledge from highly structured software and unstructured

English.

• Cross-index all the sources.

• Detect inconsistencies.

• A major consulting firm estimated that it would take 40 people two years to do the

analysis.

Understanding unrestricted natural language is still an unsolved problem.

But if the structured data is processed first, the results can be used to interpret the

unstructured English.

VAE was used to find and compare structures from different languages when translated

to conceptual graphs.

Legacy Re-engineering Task

Compare three different languages:

• 1.5 million lines of COBOL.

• Several hundred JCL scripts.

• 100 megabytes of English documentation — text files, e-mails, Lotus Notes, HTML,

and transcriptions of oral communications.

Intellitex parser used a different grammar for each language:

• First translate the structure declarations from COBOL and JCL to conceptual

graphs.

• VAE was used to find and interpret relevant passages from the English

documentation.

• Internally all information was represented in CGs.

• Output was translated to UML diagrams and English text.

Results

Job finished in 8 weeks by two programmers, Arun Majumdar and André LeClerc.

• Four weeks for customization: 

• Design and logistics.

• Additional programming for I/O formats.

• Three weeks to run Intellitex + VAE + extensions: 

• 24 hours a day on a 750 MHz Pentium III.

• VAE handled matches with strong evidence.

• Matches with weak evidence were confirmed or corrected by Majumdar and

LeClerc.

• One week to produce a CD-ROM with integrated views of the results: 

Glossary, data dictionary, UML diagrams.

Conclusions

Cyc has demonstrated that deduction alone, even with large knowledge bases, does

little to improve the flexibility and efficiency of knowledge acquisition.

The OWL ontologies are much smaller than Cyc, and even if they were as large as Cyc,

the OWL reasoners are not as powerful as Cyc.

New breakthroughs will have to come from improvements in reasoning methods other

than deduction: induction, abduction, and analogy.

VAE demonstrates that a high-speed analogy engine has great potential.

But much more R & D needs to be done.

Related Readings

For further analysis of the knowledge soup, see Chapter 6 of

Sowa, John F. (2000) Knowledge Representation: Logical, Philosophical, and

Computational Foundations, Brooks/Cole Publishing Co., Pacific Grove, CA.

A discussion of knowledge soup and its relationship to formal theories:

Crystallizing Theories out of Knowledge Soup

http://www.jfsowa.com/pubs/crystal.htm

A description of the VivoMind Analogy Engine and the Intellitex parser, co-authored with

Arun Majumdar:

Analogical Reasoning

http://www.jfsowa.com/pubs/analog.htm

The relationship of ontology to logic, metadata, metalanguages, and semiotics:

Ontology, Metadata, and Semiotics

http://www.jfsowa.com/ontology/ontometa.htm

Philosophical issues about the effect of knowledge soup on the development and

application of ontologies:

Signs, Processes, and Language Games: Foundations for Ontology

http://www.jfsowa.com/pubs/signproc.htm

Model-theoretic foundation of logics with multiple metalevels and nested contexts:

Laws, facts, and contexts: Foundations for multimodal reasoning

http://www.jfsowa.com/pubs/laws.htm

Graphic and language interfaces to intelligent systems: 

Graphics and Languages for the Flexible Modular Framework

http://www.jfsowa.com/pubs/gal4fmf.htm

A description of how the VivoMind Analogy Engine was used to support legacy reengineering:

LeClerc, André, & Arun Majumdar (2002) "Legacy revaluation and the making of

LegacyWorks," Distributed Enterprise Architecture 5:9, Cutter Consortium,

Arlington, MA. 
Evaluating Intelligence in Unmanned Ground Vehicle Teams 

Sesh Commuri1, Yushan Li1, Dean Hougen2, Rafael Fierro3

1

School of Electrical and Computer Engineering 

University of Oklahoma, Norman, OK 

2

School of Computer Science 

University of Oklahoma, Norman, OK 

3

School of Electrical and Computer Engineering 

Oklahoma State University, Stillwater, OK 

ABSTRACT 

Evaluation of intelligence in Teams of Unmanned Ground 

Vehicles (UGVs) requires the development of consistent metrics 

and benchmarks. This is a complicated process as the 

implementation of the UGVs is problem and domain specific. 

Different performance requirements give rise to different set of 

metrics making the comparison of performance between two 

implementations difficult. In this paper, we focus on three aspects 

of intelligence, namely reconfiguration, adaptation and learning, 

and communications in UGV teams and investigate the 

development of metrics for measuring their performance. We 

also investigate the available benchmarks for intelligent systems 

and verify their suitability for measuring the performance of 

UGV teams. A hierarchical architecture called Adaptation and 

Learning at All levels (AL2

) for the UGV teams is presented. 

This architecture is designed to allow for a modular and 

hierarchical approach to implement deliberative and reactive 

behaviors in teams of autonomous vehicles. In this 

implementation, system intelligence is incorporated at all levels 

of the hierarchy. The performance of the proposed architecture is 

evaluated using the metrics identified. 

Keywords: Performance Metrics, Intelligent Systems, UGVs, 

Adaptation and Learning.

1. INTRODUCTION 

The high cost associated with the acquisition and 

deployment of mobile robots motivates the development of 

low cost multi-robot teams that can function cooperatively 

to achieve specified goals. As the performance 

requirements get more stringent and the application realm 

becomes more diverse, embedding intelligence in system 

becomes a critical part of the realization of the Unmanned 

Ground Vehicles (UGV) Teams. 

 The notion of “intelligence” and the requirements for 

such intelligent systems has been discussed in detail in [1]. 

For a control system, at a very minimum level, system 

intelligence implies the ability to sense the environment, to 

make the control decisions based on the task requirements 

and to take the necessary corrective actions. At a higher 

level, system intelligence may include the ability to 

recognize objects and events, to represent the knowledge 

in a world model and to plan for the future. Intelligence at 

its highest level provides the ability to perceive and 

understand, to predict outcomes based on actions, to 

choose wisely between actions, and to maximize the 

chances of success under variety of circumstances. In 

general, intelligence embodies the ability to learn from 

experience and adapt successfully to the environment. For 

successful implementation, however, “intelligence” has to 

be formalized and the required metrics for its measurement 

developed. 

 The challenges and issues in defining performance 

metrics for intelligent systems are discussed in [2, 3]. The 

analysis of the system architecture and configuration is 

proposed to develop a measure of “Machine Intelligent 

Quotient (MIQ)” in [4]. In [5], requirement specifications 

and system verification are used to develop a formal 

method to specify the performance metrics. Techniques to 

assign metrics to intelligent systems are also explored in [6, 

7]. 

 Designing intelligent systems is a complex task 

requiring the integration of a diverse set of hardware and 

software components. Intelligence can be formally defined 

as “the ability of a system to behave appropriately in an 

uncertain environment” where “appropriate behavior 

maximizes the likelihood of the system’s success in 

achieving its goals [1]”. Such an intelligent system should 

be able to respond to sensory feedback at every level such 

that goals are achieved despite perturbations and 

unexpected feedback. Since intelligence responds to 

sensory feedback at all levels, overall effectiveness 

requires such ‘system intelligence’ to be distributed in 

nature. Therefore, any measure of the “intelligence” must 

account for the “intelligence” at each level of the system. 

Typical components that are to be looked at are: 

a. Sensors and actuators 

b. Knowledge representation and world model 

c. Planning and control 

d. Learning and adaptation 

In addition to the above, metrics are required to measure 

the level of system autonomy. Some of the measures 
proposed in literature measure the sensitivity of the 

implementation to environment and the learning 

algorithms that are implemented [8]. For a system 

comprising a single robot, some possible metrics [9] are (a) 

the ability to choose strategies or algorithms; (b) the ability 

to generate reactive and deliberative behaviors; (c) 

effectiveness in accomplishing goals and objectives; (d) 

efficiency of operations. 

 While the above metrics are adequate to describe high 

level system performance, they do not give insight into the 

functioning of UGV teams. In the case of UGV teams the 

mission complexity and uncertainty in the environment 

impose more stringent requirements on the “system 

intelligence”. In this case, the design must address 

additional issues such as: 

1) Dynamic reconfiguration of the UGV teams to meet 

mission requirements. This situation is typically 

encountered when a new team has to be formed, or 

when a team has to be augmented with additional 

resources. Dynamic modification of teams also 

occurs during formation control of UGVs. 

2) Coordination and Cooperation between team 

members, and 

3) Distributed real-time communications between team 

members and other teams. 

 These requirements have strong impact on the 

implementation of every level in the hierarchy of the 

system. Thus, in addition to the metrics for the overall 

system performance, the performance analysis requires the 

definition of metrics for each level of the hierarchy in the 

implementation. 

 In this paper, a hierarchical architecture called 

Adaptation and Learning at All Levels (AL2

), that allows 

system intelligence to be incorporated at all levels of the 

hierarchy is proposed. This architecture is modular, 

scalable and flexible. Specific requirements on the UGV 

teams are listed and their impact on the entities in each 

layer is discussed. The development of metrics is then 

discussed based on this implementation framework. The 

rest of this paper is organized as follows: Section 2 

presents the AL2

 architecture for teams of UGVs. The 

metrics needed to evaluate the performance of the team are 

discussed in Section 3. The implementation of the 

proposed architecture for the development of intelligent 

teams of unmanned ground vehicles is then presented in 

Section 4. 

2. AL2 ARCHITECTURE 

In this section, architecture is proposed that enables the 

design of complex hierarchical systems using simple 

components whose performance can be rigorously 

analyzed. This architecture, called Adaptation and 

Learning at all Levels (AL2

), allows for intelligence to be 

implemented at all levels of the hierarchy and for 

adaptation and learning occurring at different granularities 

throughout the system. 

...

S A C A A A

E A W M P A

Robot_Agent 1

S A C A A A

E A W M P A

Robot_Agent 2

S A C A A A

E A W M P A

Robot_Agent n

E A W M P A

Robot Group n

...

S A C A A A

E A W M P A

Robot_Agent 1

S A C A A A

E A W M P A

Robot_Agent 2

S A C A A A

E A W M P A

Robot_Agent n

E A W M P A

Robot Group 2

E A W M P A

...

E A W M P A

Robot Group 1

L 1

L 2

L 3

L 4

S A C A A A

E A W M P A

Deliberative Robot Agent 1

Reactive Robot Agent 1

S A C A A A

E A W M P A

D eliberative R obot A gent 2

Reactive Robot Agent 2

S A C A A A

E A W M P A

Deliberative Robot Agent n

Reactive Robot Agent n

Fig. 1 Architecture for Adaptation and Learning at All Levels (AL2) 
 The proposed architecture (AL2

) envisions one or 

more robotic agents working as a group. At the lowest 

level (L1), each robot agent has a control agent (CA), an 

actuator agent (AA), and a sensor agent (SA). The control 

agent is responsible for attaining the commanded system 

performance at the lowest level. It can command the 

sensor agent to override its output values, recalibrate its 

signal, as well as perform rudimentary signal processing 

like filtering. The AA, CA, and SA have the lowest level 

of autonomy. This level (L1) is characterized by stringent 

real-time requirements and deterministic behavior. At a 

very fundamental level, this design is adequate for a 

robotic agent to function and perform repetitive tasks in a 

structured environment. Note that, because of our 

distributed communication infrastructure, the sensor, 

actuator, and control sources (and the corresponding subagents) for a single robot agent need not be present on the 

same physical platform. For example, a platform lacking a 

camera and image processing capabilities could still 

perform leader-following if the leader platform had a rearfacing or omnidirectional camera (or other sensor) that 

could be used to sense the relative position of the follower 

platform. 

 In order to meet the requirements of fault tolerance, 

uncertainty in the system model and the environment, we 

propose a distributed architecture wherein the higher layer 

(L2) incorporates elements that instill higher-level 

intelligence in the robot. In this layer, the sensory signals 

from Layer L1 are processed by the Estimator Agent (EA). 

The output of the Estimator is then used to modify/update 

the local representation of the World Model (WM) and as 

input to the Control Agent. The distributed intelligence 

paradigm that is proposed means that EA can now include 

algorithms for fault detection, dynamic sensor 

reconfiguration, and sensor fusion at the level of a 

deliberative robot agent. The WM entity in the robot agent 

maintains information about the environment that is 

necessary for the successful tasking of the robot. Typically, 

this would include local map information, friend/foe 

classification, targets and obstacles etc. The Planning 

Agent (PA) utilizes the information from the local model 

of the world (WM) and the high-level task requirements to 

generate a plan that is communicated to the control agent 

in layer L1. The PA implements algorithms for path 

planning, obstacle avoidance, optimization, etc., for an 

individual robot. Level L2 is characterized by increased 

autonomy and less stringent real-time requirements. 

 A team of robots consists of a number of individual 

robot agents possibly with differing sensor/actuator suites 

and capabilities. The coordination between these agents is 

managed by the PA entity at the level of the robot group 

(L3). Information sharing between L2 entities is controlled 

by the entities in L3. This increases the security of the 

implementation because the L2 entities can function 

independently of each other, while still functioning in a 

coordinated manner. The primary function of the entities 

in Layer 3 is to coordinate the working of the robot agents 

in the group. L3 handles all reassignments of tasks 

between different robot agents in L2. Introduction of new 

robot agents or sensor suites, etc., are the exclusive domain 

of L3. The outputs of all the EAs in layer L2 provide the 

input to the EA module in L3. Team-level sensor fusion 

amongst the different robotic agents is accomplished by 

the EA at L3. This EA module is used to update the world 

model (WM) in Layer 3. This WM also manages the 

information sharing among the robot agents in L2. The 

planning agent (PA) in this layer does the task 

decomposition from the mission requirements and updates 

the individual PAs in L2. It is to be noted that the 

architecture specified is independent of hardware and 

software implementations and individual elements in L2. 

 Layer 4 (L4) manages the coordination between 

groups of robot agents. The highest level of intelligence 

and autonomy and the lowest level of real-time criticality 

characterize L4. Dynamic reassignment of the 

responsibilities of each group is handled by L4. 

 The proposed architecture will enable the 

development of groups of unmanned ground vehicles that 

can be dynamically configured and retasked. The 

architecture is flexible and is not dependent on the type of 

controllers or algorithms implemented in any given layer. 

3. DEVELOPMENT OF METRICS FOR 

SYSTEM INTELLIGENCE 

In this section, the metrics required to evaluate the 

performance of the UGV teams with respect to 

reconfiguration, cooperation and the real-time 

communication between team entities are addressed. 

3.1 Dynamic Reconfiguration of Hardware and 

Software 

To meet the operational requirements for different tasks, 

the system should have the intelligence to implement 

different software and hardware configurations 

dynamically at the every level of the hierarchy. Plug-andplay sensors and actuators require relevant signal 

processing elements and software drivers to be loaded and 

the data made available seamlessly to the application. Fault 

handling on the other hand might necessitate the routing of 

signals dynamically through a different part of the system 

in order to bypass a faulted element. The capability of the 

system to handle these requirements can be evaluated by 

the following set of metrics. 

a. Is the system reconfigurable? 

 The rigidity of the implementation can be assessed by 

checking the amount of reconfigurable entities in the 

implementation. A typical implementation may consist of 

fixed hardware and software components and some 
modules whose functionality can be modified at run-time 

either by the user or by other processes. The amount of 

reconfigurable resources as a ratio of the overall system 

resources is a measure of the reconfigurability of the 

system. 

b. Is the system reconfiguration static or 

dynamic? 

 Static reconfiguration requires the system to be taken 

off line and reconfigured before it is deployed. On the 

other hand, dynamic reconfiguration can take place while 

the system is under operation. Dynamic reconfiguration is 

essential when it is not feasible to take the system off-line 

to implement changes. 

c. Can the system be fully / partially 

reconfigured? 

 Full and partial reconfigurations are important aspects 

of the design of intelligent systems. Systems typically need 

to execute special tests at startup to verify proper system 

functioning. Once the startup tests are complete, the 

system can transition to the “run-time” mode. While it is 

easy to load test software to run system tests at startup, the 

tests that can be run are constrained by the hardware. By 

incorporating the ability to change the configuration of the 

hardware, for example by using FPGA devices, the same 

hardware can be used for system tests at startup and then 

“fully” reconfigured for run-time operations. The ability to 

“fully” reconfigure the hardware is also essential to the 

retasking of the individual robot. When the robot is 

retasked, sensor and actuator configurations can be 

selected that adapt the robot for the specified task. Since 

the embedded hardware can be optimized for the specific 

task, the overall performance can be improved without an 

increase in system cost. 

 Often, it is required to re-route the signals to 

accommodate for faults or add additional circuitry to 

handle signals from new sensors that come on-line. In such 

circumstances, unused portions of the FPGA can be 

configured to handle this requirement while the rest of the 

device is unaffected. Such reconfiguration, called Partial 

Reconfiguration, is essential to support retasking of 

individual robots, plug-and-play transducers, and for fault 

accommodation. 

3.2 Coordination and Cooperation Between 

Team Members

 

Traditional control theory enables the design of controllers 

in a single mode of operation in which the task and the 

controlled plant are fixed. Contrary to this, in the case of 

UGV teams, team members usually interact with each 

other and with uncertain or unstructured environments. 

The team is to reach a goal destination, negotiate around 

obstacles and satisfy constraints on the formation. Thus, 

any measure of performance of the UGV teams has to 

address the ability of the teams to coordinate and cooperate 

with another in order to successfully accomplish the 

overall mission objective. The effectiveness of the 

implementation of UGV teams for coordination and 

cooperation among team entities can be measured by the 

following set of metrics. 

a. Is the UGV team capable of executing simple 

formations? 

 The ability of the UGV team to execute simple 

formations like leader-follower, straight line, and convoy 

are a good indication of the coordinated activity among the 

members of the UGV team. 

b. Is it possible for individual members in the 

team to seamlessly share sensory information, 

world models, and data? 

 The performance of the UGV team can be 

significantly improved if the sensors could be calibrated 

using reference data gathered by an external entity. The 

ability to use sensory information from other team 

members also extends the capability of a team in the face 

of sensory failures. Successful implementation of 

intelligent UGV teams requires the ability for each 

member of the team to benefit from the knowledge gained 

by other team members. Thus by sharing the world models 

and the knowledge, UGVs can demonstrate behaviors that 

are not programmed. Similarly, sharing of performance 

data between members is critical to the efficient operation 

of the UGV team. 

c. Can an UGV team be dynamically modified by 

the addition or removal of a team member? 

 Operational damage to an UGV or changing mission 

requirements often requires augmentation of an UGV team 

with additional resources. The ability to recognize the 

availability of additional resources and retask each of the 

UGVs in the team is a measure of the dynamic adaptability 

of the UGV team. This characteristic is also important in 

cases where an UGV team moving in a formation has to 

navigate around a dynamic obstacle. In this case, the team 

has to split into two sub-teams, maintain sub-formations 

while avoiding the obstacle and then rejoin in the original 

formation. 

 
3.3 Distributed Real-Time Communications 

Real-time communications are essential to support 

other functions within the UGV teams. The 

communication scheme has to be flexible and allow 

for communication of differing transmission rates, 

media, and security. The ability of the system to 

dynamically select channels of communication to 

improve performance and reduce power consumption 

is critical to the performance of the team. The 

following characteristics can be used as a measure of 

the performance of the communications scheme. 

a. Is there a mechanism for the intra-layer 

and inter-layer communications? 

 Teams of UGVs have to communicate and 

coordinate at several levels [11]. Therefore in each 

layer, modular implementation of the entities with 

appropriate communication interfaces is crucial for 

the successful coordination between UGVs. The 

communication mechanism will have to provide 

visibility into each entity at every level of the 

implementation. For example, the ability to share 

sensory data, world models, or plans between 

different UGVs in a team is essential to the 

implementation of intelligent UGVs. Intra-layer and 

inter-layer communication is essential for the 

intelligence of an UGV while communication 

between different UGVs and teams of UGVs is 

crucial for the implementation of intelligent teams of 

UGVs. 

b. Is the communication scheme used flexible? 

 The higher layers in the implementation of an 

UGV are typically characterized by abstract entities 

where intelligent decisions are made. The lower 

layers on the other hand, are characterized by realtime control modules where traditional closed loop 

control decisions are taken. The varied nature of 

communication at each level in the implementation of 

an UGV implies that the communication scheme 

employed must be flexible enough to enable the 

dissemination of high-level abstract information as 

well as the low-level real-time data. 

b. What are the communication mechanisms 

and the guaranteed performance? 

 Successful operation of the UGV teams requires 

a number of communication techniques. Commonly 

implemented ones are the ability to provide queryand-response mechanism, broadcast and periodic 

transmission of data between different entities in the 

implementation. Key properties such as bandwidth, 

transmission rates, protocol overhead, transmission 

error rates, error correcting methods etc. are to be 

analyzed to ensure that the communications do not 

become a bottleneck in the performance of the overall 

system. 

4. CASE STUDY 

The proposed framework is tested by implementing 

the L1 layer of the proposed architecture on the 

Xilinx Virtex-II Pro platform [13]. This platform was 

selected based on its capability to implement 

reconfigurable architectures, and the excellent 

development tools and product support. The Virtex-II 

Pro XC2VP4 has a PowerPC core, 6768 logic cells, 

504 KBits BRAM, 4 3.125 Gbps RocketIO 

transceivers, and 3.01 Mbits configuration space. 

 The Xilinx Virtex-II Pro device is a user 

programmable gate array with embedded PowerPC 

processor and embedded high-speed serial 

transceivers. The Xilinx Virtex architecture is coarse 

grained and consists of a number of basic cells called 

configurable logic blocks (CLBs). These logic blocks 

are arranged in rows and columns, with each CLB 

consisting of four logic cells arranged in two slices. 

Each CLB also contains logic that implements a fourinput look up tables (LUTs). Each slice contains two 

function generators, two storage elements, arithmetic 

logic gates, large multiplexers, wide function 

capability, fast-carry look ahead chains, and 

horizontal cascade chains. The function generators 

are configurable as four input look up tables (LUTs), 

sixteen bit shift registers, or as sixteen bit selective 

RAM memory. Each CLB also has fast interconnect 

and connects to a generalized routing matrix (GRM) 

to access general routing resources. The Virtex-II Pro 

has SelectIO-Ultra blocks (IOBs) that provide the 

interface between the package pins and the internal 

configurable logic. Active Interconnect Technology 

connects all these components together. The overall 

interconnection is hierarchical and is designed to 

support high speed designs. 

 The programmable elements in the Virtex-II Pro, 

including the routing resources, are controlled by 

values stored in the static memory cells. The device is 

configured by loading the bitstream into the internal 

configuration memory. These values can be reloaded 

to change the functions of the programmable 

elements. The Xilinx Virtex family of FPGAs 

supports both partial as well as dynamic 

reconfiguration. Partial reconfiguration can be 

achieved in one of the two ways, namely Modulebased partial reconfiguration and difference-based 

reconfiguration. In the module-based reconfiguration, 

the entire module can be reconfigured. The height of 

the reconfigurable module is the height of the device 

and the module can cover one or more columns. In 

difference-based reconfiguration, the reconfiguration 

is done by making a small change in the design, and 

then generating a bit-stream based only on the 

differences in the two designs. Switching the 

configuration from one implementation to another is 

easy and very quick. 

 The system is designed with PPC405 processor 

core, SDRAM controller connected to Processor 

Local Bus (PLB) and general purpose Inputs-Output 

(GPIO) devices like Leds, Push buttons, UART and 

dip switches are connected to its On-chip Peripheral 

Bus (OPB). These are the components available on 
Fig. 2. Implementation of PWM motor control with dynamic reconfiguration for fault accommodation. 

Fig. 3. Neural Network based compensation of actuator nonlinearities. 

Fig. 4. Implementation of a one-layer Neural Network in Simulink using Xilinx Toolset. 
the board, so the first step is to verify the proper 

functionality of all these components. To do this, the 

processor boots up with a configuration file to test all the 

components. On successful completion of built in self test, 

the processor fetches the second configuration file to 

configure itself and the board, switching into operational 

mode. If subsequent reconfiguration of the system requires 

additional components, then the configuration files can be 

loaded dynamically into the FPGA. For example, if serial 

communication capability is required, then a preconfigured 

UART module can be loaded into the FPGA and the 

relevant software drivers activated. This can be achieved 

during the operation of the system with configuration 

times of the order of micro-seconds. 

 In the second design example, a PWM generator is 

implemented in the hardware to control the drive motors of 

the robot (Fig. 2). Timer 1 (pwmTimer) is configured to 

generate the PWM signal while Timer 2 (opbTimer) is 

configured to sense the feedback signal. If a fault is 

detected in the “sense” circuit during operation, then a 

different sensing circuit is dynamically created and the 

signals routed through it. The control cycle in this example 

was executed in real time with a sampling rate of 20 millisecs. The time for reconfiguration was of the order of a 

few micro-seconds showing that dynamic fault 

accommodation was achieved in real time. 

 In the third design example, a Neural Network (NN) is 

implemented in the FPGA to compensate for actuator 

deadband (Fig.3). The controller continuously monitors the 

output and dynamically instantiates the neural network in 

the FPGA when the performance degrades significantly 

due to load dependent deadband in the actuator dynamics. 

The Neural Network is modeled and designed in Simulink 

using the Xilinx toolset provided by Mathworks Inc. (Fig. 

4). Once the design has been successfully validated, a 

configuration bit stream can be generated that allows for 

dynamic creation of the NN module in the hardware. 

5. CONCLUSIONS 

 In this paper, architecture was presented that 

facilitates the implementation of teams of intelligent UGVs. 

Three aspects of intelligence, namely reconfiguration, 

adaptation and learning, and communications in UGV 

teams were investigated and metrics for measuring their 

performance were proposed. The performance of the 

proposed architecture was evaluated using the metrics 

identified. 

REFERENCES 

[1]. J. S. Albus. Outline for Theory of Intelligence. IEEE 

Trans. System, man and Cybernetics, Vol. 21, No.3, 

pp473-509, 1991. 

 [2] J.M. Evans, E.R. Messina, Performance Metrics for 

Intelligent Systems. . Proc. of Performance Metrics for 

Intelligent Systems Workshop. 2000 PerMIS Workshop, 

2000. 

 [3] L.A. Zadeh. The Search for Metrics of Intelligence- A 

Critical View. Proc. of Performance Metrics for Intelligent 

Systems Workshop. 2000 PerMIS Workshop, 2000. 

[4] E.C. Chalfant, S. Lee. Measuring the Intelligence of 

Robotic Systems: An Engineering Perspective. 

Proceedings of International Symposium on Intelligent 

Systems. Gaithersburg, MD. October, 1999. 

[5]. Y.Zhang, A.K. Mackworth. Formal Speification of 

Performance Metrics for Intelligent Systems. Proc. of 

Performance Metrics for Intelligent Systems Workshop. 

2000 PerMIS Workshop, 2000 

[6]. C. Schlenoff, L. Welsch, R. Madhavan, N. 

Zimmerman, Towards Measuring the Performance of 

Architectural Components of Autonomous Vehicular 

Systems. 2002 PerMIS Workshop August 13-15, 2002. 

[7]. J. S. Albus. Features of Intelligence Required by 

Unmanned Ground Vehicles. Proc. of Performance 

Metrics for Intelligent Systems Workshop. 2000 PerMIS 

Workshop, 2000. 

[8] A.Yavnai. Metrics for System Autonomy, Part I: 

Metrics Definition. Proc. of Performance Metrics for 

Intelligent Systems Workshop. 2000 PerMIS Workshop, 

2000 

[9] R. Finkelstein. A Method for Evaluating the ‘IQ’ of 

Intelligent Systems. Proc. of Performance Metrics for 

Intelligent Systems Workshop. 2000 PerMIS Workshop, 

2000. 

[10] Sesh Commuri, Yushan Li, Dean Hougen, Rafael 

Fierro. Designing for System Intelligence. Proceedings of 

the 5th IFAC Symposium on the Intelligent Autonomous 

Vehicles, Lisbon, Portugal, July, 2004. 

[11] R.Muthuraman, A. Fajebe, S.Commuri. Intelligence 

in Embedded Controls-A Case Study. Proceedings of the 

IEEE Region 5 Technical Conference, April 2004. 

[12] S. Donti, and R. L. Haggard, “A survey of 

dynamically reconfigurable FPGA devices, “ Proc. IEEE., 

vol. 8, pp. 422-426, 2003. 

[13] Xilinx, Inc., Virtex-II Pro: Platform FPGA Handbook, 

UG012, v 2.0., 2002. 
Metrics for Intelligent Autonomy 

S. O’Day 

Eagan, McAllister Associates 

47332 Eagan, McAllister Lane 

P.O. Box 986 

Lexington Park, MD 20653

M. Steinberg, C. Yglesias 

Office of Naval Research 

K. Bonnevier, T. Moulds 

NAVAIR 

Patuxent River Naval Air Station, MD 

R. Sincavage, M. Ricard, M. Cleary 

Draper Laboratory 

555 Technology Square 

Cambridge, MA 02139 

M. Curry, T. Sliski, J. Tierno 

Alphatech, Incorporated 

6 New England Executive Park 

Burlington, MA 01803 

J. Clark 

Lockheed Martin 

Fort Worth, TX 

F. Snyder 

Northrop Grumman Electronic Systems 

Pittsburgh PA 

ABSTRACT 

Intelligent Autonomy (IA) is a multi-year program within the Office 

of Naval Research (ONR) Autonomous Operations (AO) Future 

Naval Capabilities (FNC) program. The primary goal of the effort is 

to develop and demonstrate technologies for highly automated and 

fully autonomous mission planning and dynamic re-tasking of 

multiple classes of Naval unmanned systems and minimization of 

human intervention in unmanned vehicle operations. This technology 

is being applied to both individual and teams of unmanned air, 

surface, ground, and undersea vehicles for a variety of mission areas 

including reconnaissance/search, persistent surveillance, tracking, 

and some limited application to strike. Autonomy technologies will 

be matured through a series of phased demonstrations to allow low 

risk transition to current and future Navy and Marine Corps systems. 

Demonstrations will be done using both real vehicles and simulation. 

Some of the major simulation demonstrations will be done within the 

context of a simulated warfare environment at the Naval Air Systems 

Command based around the Air Combat Environment Test & 

Evaluation Facility (ACETEF) and the Unmanned System Research 

and Development Lab (USRDL). The demonstrations at NAVAIR 

will utilize much of the architecture and many of the assets from the 

NCW4.0X Virtual Laboratory (V-LAB) project. Metrics for testing 

of IA software in this environment are currently being developed. 

This paper will discuss some candidate performance metrics that are 

currently being considered for evaluation of the Intelligent Autonomy 

technologies. 
KEYWORDS: unmanned aerial vehicle, unmanned undersea 

vehicle, mission planning, autonomous control, JIMM 

1. INTRODUCTION 

The Intelligent Autonomy Effort under the Autonomous 

Operations Future Naval Capability is developing a range of 

technologies that will be challenging to effectively evaluate 

using traditional metrics. The goals of the Intelligent 

Autonomy (IA) effort IA are to 

•Provide autonomy software for highly automated and fully 

autonomous dynamic retasking of multiple classes of Naval 

unmanned systems to perform littoral reconnaissance, search, 

persistent surveillance, and to a limited extent tracking and 

strike. 

•Minimize human intervention via autonomous and highly 

automated mission planning/replanning functions and operator 

aids such as alert management and plan understanding for 

individual vehicles and teams of vehicles. 

•Enable limited automated surveillance and reconnaissance 

data processing for surface and shoreline object detection and 

classification to provide autonomous replanning based on 

sensed information, bandwidth reduction, and operator 

workload reduction. 

The technologies demonstrated under the IA product lines will 

be applicable to multiple types of Naval unmanned vehicles 

including unmanned air, undersea, ground, and surface 

vehicles with a focus on air and undersea vehicles and control 

stations. This effort will leverage numerous DOD programs in 

autonomy to support specific Navy and Marine Corps unique 

and essential needs. Intelligent Autonomy technologies will 

be demonstrated through a series of phased demonstrations to 

allow low risk transition to current and future Navy and 

Marine Corps systems. The primary areas being developed 

and demonstrated under the IA program are: 

UxV High-Level Planning/Replanning 

Lead Performers: Alphatech, Draper Laboratory 

Allocate mission tasks to available platform/payload types out 

of a team of 5-10 heterogeneous vehicles and determine an 

optimal sequence of mission tasks with associated time 

windows/constraints based on high-level tasking (platform 

availability, team mission tasks, priorities, and constraints). 

UAV Dynamic Replanning 

Lead Performer: Lockheed Martin, Ft. Worth 

Produce UAV mission plan that optimizes survivability & 

employment of on-board capabilities while meeting an ordered 

set of mission objectives and constraints. 

UUV On-Board Dynamic Mission Replanning 

Lead Performer: Draper Laboratory 

Generate minimum-cost, energy efficient, safe routes to 

achieve combination of mission tasks within constraints. 

Alert Management & Replan Assessment 

Lead Performer: Lockheed Martin, Ft. Worth 

Replan Assessment to analyze mission plan changes, 

monitor/assess contingencies, assess contingencies, and trigger 

a replan or alert if necessary. Alert Management to determine 

the level and type of alerts received, store alerts received and 

forward them to be displayed, and support the operator in 

recovering the context of tasks interrupted. 

Mixed-Initiative Interface Manager 

Lead Performers: Lockheed Martin ATL, Charles River 

Analytics, and Aptima 

Display relevant mission information, provide planunderstanding capabilities, and enable the operator task the 

vehicles and set the level of autonomy. 

Distributed Cooperative Control 

Lead Performer: Alphatech 

Enable autonomous mission replanning among teams of 

vehicles with limited communications 

Maritime Image Understanding 

Lead Performer: Northrop Grumman Electronic Systems 

Develop video processing technology in the river and harbor 

domain. Detect and classify mission relevant objects to 

support autonomous navigation and surveillance. 

2. PROJECT DESCRIPTION AND 

SCHEDULE

Initially, the developers will demonstrate the functionality and 

capability of their products using medium to high-fidelity 

simulation models at their facilities. Later, software algorithms 

are planned to be integrated with Naval control stations or 

vehicles to enable testing and maturation of the software 

products. The algorithms will be demonstrated in both 

simulation and hardware/in-water demos. 

NAVAIR will provide a test bed for development using the 

Air Combat Environment Test & Evaluation Facility 

(ACETEF) and the Unmanned System Research and 

Development Lab (USRDL). A specific Joint Integrated 

Mission Model ACETEF (JIMMACE) port scenario database 

will serve as the warfare environment for mission planning 

system development and the Tactical Control Station (TCS) 

will serve as a baseline for operator station development. 

3. WARFARE ENVIRONMENT 

JIMMACE may cede control of specific player tactics and 

system functions to external IA hardware or software assets 

that interface to JIMMACE shared memory. Object instances 
are defined in the JIMMACE scenario database (SDB). The 

extent of asset control is defined via statements in the control 

database (CDB). The types of objects (players, platforms and 

systems) in the environment, the tactics that these objects 

execute as well as the command, communications and control 

architecture are being defined in the JIMMACE type database. 

The JIMMACE model will provide the warfare environment 

for integrated IA demonstrations. IA assets access and control 

parts of the JIMMACE warfare environment via shared 

memory network interfaces. DIS, HLA and UDP datagram 

socket connection protocols are used to transmit the data 

between IA assets and shared memory. The JIMMACE model 

creates and fills information into shared memory based on 

databases written in its native language (which consists of 

English language phrases which are combined in a 

straightforward syntax). 

4. OPERATOR ENVIRONMENT 

The IA program is focused on operator functions related to 

mission management only. It is assumed that either the 

vehicles are highly autonomous or that there are additional 

operators or operator functions concerned with vehicle 

management issues, such as shipboard recovery and air traffic 

management issues for UAV's. The system operators will 

interface with the IA hardware and software assets through the 

TCS interface and the new IA operator interface modules. 

Serving as a network interface between the operator interface 

(TCS and the new IA OI’s) and the warfare environment will 

be the Unmanned Simulation System (USS) stimulator. The 

USS will provide a way for the evaluators to insert real-time 

scenario modifications such as vehicle or sensor cautions, 

warning, and emergencies. This will be used as part of the 

evaluation metrics in testing the interaction between the IA 

technologies and the operator(s) in relation to SA and 

workload. 

The baseline operator environment will be a 1-3 person team 

that may consist a mission commander, vehicle operator, 

and/or a sensor operator. The number of operators depends 

on the type and number of unmanned vehicles and the 

complexity of the mission tasks. A secondary baseline 

derived from the JUCAS concepts will be a five-person team 

that will dynamically split vehicle control aspects with sensor 

control and C4I aspects. 

The USS will interface with JIMMACE via a HLA interface. 

The USS is a CORBA based architecture and supports custom 

interfaces via UDP and TCP. 

5. CANDIDATE METRICS 

This section will describe some of the major candidate metrics 

that are being considered for use on the IA effort. There are a 

variety of useful measurements that can characterize the 

engineering quality of unmanned vehicle simulation, 

intelligent autonomy, and operator control station software. 

These can be roughly categorized as: 

• response of system components to a range of initial input 

parameters 

• human factors of operator mission management and 

situational awareness 

• response of system components to changes in the simulated 

warfare environment during execution 

Metrics relating the unmanned vehicle simulation system 

performance to mission goals include: 

• optimization of the number and mixture of unmanned 

vehicles to maximize the number of successful missions 

• impact of mission re-planning time on mission success 

• optimum distance between assets and targets for maximal 

mission success 

• impact of reactive/creative maneuvers on mission success 

• loss of assets in mission completion/objectives completed 

• operator/vehicle ratio 

The response of the system to different initial conditions can 

be measured in terms of time and impact on mission success. 

Top-level parameters, which can be varied, include: 

• geographic size of gaming area and placement of assets 

• weather, terrain and other environmental factors 

• number of missions 

• number of each type of unmanned vehicle 

• mission re-planning cycle time 

• extent of UV intelligent tactics 

• types of missions within a particular scenario 

Each proposed system has a number of engineering metrics 

which also relate to mission flexibility and success. 

5.1 Mission Software Component Metrics 

The IA project accepts certain scenario dependent mission 

coverage metrics to evaluate the IA mission-planning 

components. The time it takes to turn around a mission plan or 

re-plan is an obvious metric. This can be dependent on the 

number of constraints, number of total missions underway and 

on a variety of warfare environment parameters. The goal is 

then to maximize the number of simultaneous missions that 

can be executed within the context of the following: 

• Number of simultaneous mission tasks that the system can 

handle 

• Number of mission task types that the system can handle 

• Planning exception rate (dropped tasks over total tasks) 

• Fraction of mission constraints not met (if feasible) 

In the area of dynamic performance metrics, it is hoped that 

the time elapsed between task appearance and completion is 
minimized within the context of the following scoring ratios 

S(t) where t is the time from the beginning of the scenario: 

• Optimization of mission-specific cost-measures 

• Discounted optimization of mission-specific cost-measures 

to emphasize timeliness 

Stability/sensitivity metrics are used to avoid frequent changes 

in plans that may have a detrimental effect on mission 

performance and operator situation awareness. One such 

measure is that of “thrashing” in tasking where one takes the 

time elapsed between execution of one task and the last 

change of the preceding task. This can also be examined as a 

function of communication bandwidths, error rates, and 

scenario variation. 

5.2 Operator Station Metrics 

Since the IA program is focused on operator functions related 

to mission management only, there are some differences from 

the types of metrics traditionally used for operators directly 

controlling the vehicle. Of particular concern is the neglecttolerance of the system. This concerns both how well the 

autonomous system behaves when there is limited human 

intervention and how well the human operator is able to 

maintain situation awareness when not constantly in the loop 

or when managing multiple vehicles and mission tasks. The 

impact of human performance on the overall system can 

appear at several levels: 

• system interoperability level ( with external assets) 

• software system level (e.g. efficiency and accuracy of UV 

mission prosecution by this system) 

• operator station component level 

System level measures can be used to identify the decisionmaking roles in which the human is most influential and 

effective relative to the capabilities of the automation. 

Measures should be made under varying levels and types of 

human intervention for factors such as 

• Speed and accuracy for decisions and actions 

• Time to respond to critical events 

• Duration of mission activities 

• Ratio for completion of “Mission-Critical Objectives” vs. 

“Secondary Objectives” 

Task loading metrics are critical for estimating the required 

number of operators required for a mission. This can be 

drawn out from the speed and accuracy of task completion for 

different levels of task demands associated with the mission 

(e.g., the number and rate of required tasks for successful 

mission completion; complexity of the mission, etc.). 

Objective measures can also be used to identify the points at 

which the operator begins either shedding tasks or failing to 

achieve accurate task completion. 

Another important type of metric is subjective workload 

measures (i.e. NASA-TLX). These enable operators to rate 

their experience of mission difficultly/cognitive demands for 

both the overall workload of the mission and the workload 

associated with select critical incidents and mission phases. 

These measures are helpful for identifying the appropriate 

distribution of task load and organizational structure for a 

team of operators and the areas where additional automation 

may be desired. 

Examples of relevant metrics are: 

• the quality and extent of operator station training that is 

needed for operators to be effective in using the system 

• speed of task completion vs. mission completion 

requirement speed 

• accuracy of task completion 

• identification of points at which critical tasks are dropped 

• mission workload (overall and for critical tasks) 

• reduction of required operators without impact to mission 

effectiveness 

For the operator to achieve effective mission management of 

the system, it is important to maintain situation awareness to 

the progress of the mission. There are a number of subjective 

measures that can be used where operators rate their 

understanding of the situation. There are also objective 

measures such as “blanking the screen” and asking the 

operator to answer questions about key features of the 

situation & make predictions about expected mission progress. 

A final area is SA for critical incidents. These measures can 

be used to identify the effectiveness of user interface displays 

in allowing the operator to monitor key events relevant to 

mission tasks. 

Some subjective human performance measures include: 

• operator understanding of the mission complexity 

• SA during the mission 

• operator correctly using automated capabilities 

• operator trust of automated capabilities 

• efficiency and accuracy of decision-making 

• operator effectiveness in mission prosecution 

These measures can also be used to judge the effectiveness of 

the system concept of employment. 

Factors, which will affect the outcome of such measurements, 

are: 

• the background of the operator 

• the number of operators 

• the quality and extent of operator training 

• quality of the operator interface software 

• the commonality to other operator interfaces of relevant 

systems 

• complexity and tempo of the mission 

• the level of autonomy of the vehicle 
• the complexity of the scenario 

5.3 Maritime Detection and Classification Metrics 

Images collected and processed by unmanned vehicles are 

useful to mission planning if they provide detailed topological 

and/or object location and identification information. 

These capabilities may be described by the following 

measures: 

• accurate spatial digitization of objects and environment by 

the image processing algorithms 

• robustness of image processing algorithms in varied 

environments 

• ability of algorithms working with COTS products to do 

real-time image processing and object recognition 

• ability to derive understanding/real-time map of harbor and 

river environments from vehicle ISR image processing 

• efficiency with which real-time image processing results can 

feed mission re-planning 

5.4 JIMMACE System Modeling 

The JIMMACE model in conjunction with a shared memory 

interface can be used to model an idealized mission planner 

and fully automated mission control operator station. 

JIMMACE tactics can be employed to simulate a systems with 

varying degrees of autonomy. JIMMACE simulated players 

can assume the role, mission and function of operators and 

mission planners. Metrics can be extracted from the model 

output for comparison with the mission planning components 

and manned operator stations to identify inefficiencies. 

 

6. SUMMARY 

There is still a great deal of uncertainty about how best to use 

metrics to evaluate future autonomous system. This paper 

discussed a range of approaches to metrics that are currently 

being examined for use in planned demonstrations with a wide 

variety of autonomy components. Experimentation with 

different metrics over the course of these demonstrations will 

be help better define under what circumstances a particular 

metric is appropriate and useful. 

7. REFERENCES

 [1] J. McMaster, S. O’Day, J. Sarratt, “Millennium Challenge 

2002 Fleet Battle Experiment Juliet Analytical Excursions 

with JIMMACE”, 9th ITEA Modeling and Simulation 

Workshop, Las Cruces, NM, December 8-11, 2003. 
Measuring Autonomous UAV Surveillance Performance 

Michael Freed, Robert Harris, Michael Shafto 

{mfreed, rharris, mshafto}@arc.nasa.gov 

NASA Ames Research Center 

ABSTRACT: We describe an approach to evaluating 

algorithmic and human performance in directing UAV-based 

surveillance. Its key elements are a decision-theoretic framework 

for measuring the utility of a surveillance schedule and an 

evaluation testbed consisting of 243 scenarios covering a welldefined space of possible missions. We apply this approach to two 

example UAV-based surveillance methods, an algorithms called 2-

opt and a human-directed approach, then compare them to identify 

general strengths and weaknesses of each method. 

UAV-based Surveillance

Aerial reconnaissance, surveillance, and other observation 

tasks have been primary aircraft applications since the early 

days of powered flight. They remain key activities in 

domains from military and security operations to land 

management and scientific research. However, airborne 

observation is typically a deadly dull process that strains the 

vigilance and morale of human pilots and makes poor use of 

their costly, hard-won skills. Thus, following the rule of 

“dull, dirty or dangerous,” it is considered an excellent 

application for autonomous vehicles. Unmanned aerial 

vehicles (UAVs) have been employed in this capacity for 

decades, though almost exclusively for reconnaissance (DoD 

2002). Technological improvements combined with 

increasing investment and interest in UAVs promise to 

increase their capabilities and availability, thus enabling 

more diverse and demanding missions. Of particular interest 

to several operational communities are missions using UAVs 

to maintain “situation awareness” by continuous or periodic 

surveillance. 

Autonomous surveillance of spatially separated sites 

raises issues beyond those related to reconnaissance at a 

single site. In particular, since a given UAV can only be at 

one place at a time, it must be treated as a limited resource 

that needs to be allocated as effectively as possible. 

Effectiveness, in this case, means providing the best possible 

information to the user at the best possible time – i.e. 

maximizing the value of returned information. For any 

surveillance agent, airborne or otherwise, this entails a 

variety of interlinked choices about which sites to visit over 

the course of a mission, how often to visit each site, what 

paths to take, how long to spend observing, and what kind of 

measurements to take (cf. Sacks (2003) for a related 

discussion on police patrol, Carbonell (1969) regarding 

human visual scanning of instruments and Koopman (1956) 

regarding submarine-based search). 

Factors specific to aerial vehicles affect what kind 

of algorithms can most effectively make these decisions. For 

instance, Massios et al. (2001) have studied the problem of 

optimizing surveillance for autonomous ground vehicles 

(UGVs) operating inside buildings. In this case, the problem 

of deciding where to go next is highly constrained by the 

structure of the building while the problem of how to get to a 

location not immediately adjacent requires path-planning. 

With UAVs, the situation is reversed. Sites of interest may 

all be accessible by a direct path, reducing the need for pathplanning but leaving the problem of where to go next 

physically unconstrained. A second factor, wind, usually has 

little effect on UGVs, but has a large effect on UAVs, 

increasing or reducing required traverse time between almost 

any two sites. Algorithms for UAV-based surveillance 

should thus treat expected wind conditions (including 

variability) as a central parameter and should adapt 

dynamically to changes in wind speed or direction. 

Differences in vehicle mobility and vantage 

together create a third significant difference between UGVand UAV-based surveillance. Because of its altitude, a UAV 

will frequently be able to observe a site from a distance 

without obstruction and thus may not have to travel the full 

distance to that site. And, due to the low friction on an air 

vehicle in aerodynamic flight, a UAV making fast-time 

observations may be able to retain most of its speed when 

transitioning between approach to one site and approach to 

the next. A surveillance algorithm that takes advantage of 

these aviation-specific factors should perform significantly 

better than one that does not. 

Our work on UAV-based surveillance represents 

one part of a larger project to develop a practical and flexible 

UAV observation and data-delivery platform. The 

Autonomous Rotorcraft Project (Whalley et al. 2003) is an 

Army/NASA collaborative effort combining advanced work 

on avionics, telemetry, sensing, and flight control software in 

addition to software for high-level autonomous control. The 

base platform selected for the project, a Yamaha RMAX 

helicopter, has been enhanced in a variety of ways that 

increase its potential effectiveness as a surveillance vehicle. 

Flight control software allowing it to fly aerodynamically 

extends the vehicle’s speed and improves its fuel-efficiency, 

thus extending both operating range and base flight duration 

(60 minutes hovering with full payload). The vehicle 

includes a range of sensors and the capacity to integrate and 

control additional sensors as demanded by particular 

missions. Its high-level autonomy component, Apex (Freed 

1998), incorporates reactive planning and scheduling 

capabilities needed for mission-level task execution, 

navigation, response to health/safety contingencies and 
interaction with human users. To enable the system to

become highly effective for surveillance, scheduling 

capabilities must be extended based on algorithms of 

demonstrated effectiveness in diverse mission scenarios 

relevant to the Army and to NASA. 

The diversity of possible surveillance missions

poses particular challenges. First, an algorithm that performs 

well in certain kinds of missions may perform poorly in

others. For instance, an algorithm that does well optimizing 

observations for a small number of closely spaced sites may 

not scale well to missions involving a large number of sites 

spread out over a wide area. Similarly, an algorithm that 

assumes that information obtained at different sites becomes 

obsolete at equal rates or that the value of making an

observation at one site necessarily equals that at another will 

not perform well when such assumptions do not hold. It is

not yet well-understood which attributes are most significant

in distinguishing one mission from another. While the

number of sites to be observed is clearly an important factor,

the importance of other factors, e.g. the centrality of the 

takeoff/land location with respect to the set of target sites, is 

less clear. Finally, for a single system to provide

autonomous surveillance capability for a broad range of

missions requires an underlying theory of surveillance. If 

users need to communicate mission goals in terms of that 

theory, its generality is likely to pose difficulties for most 

users (Freed et al. 2004). For instance, a theoretical

foundation based on mathematics unfamiliar to most users 

(as will be described below) may require them to specify the 

mission in terms of seemingly exotic mathematical 

parameters. 

To meet these challenges requires: (1) developing 

methods for measuring the effectiveness of a given algorithm

and for comparing the performance of an algorithm to that of

human operators (i.e. to current practice); (2) creating 

planning and scheduling algorithms that perform surveillance

effectively in significant parts of the space of possible

missions; and (3) addressing issues of usability in the 

specification of missions by non-expert users. In this paper,

we describe our work in the first of these areas to create a 

framework for evaluating algorithm performance and human 

performance at surveillance tasks. We then illustrate the 

application of the framework using two example surveillance 

techniques – a modified 2-opt algorithm and human-directed

surveillance. 

Measuring Surveillance Performance

The first issue in devising an evaluation framework is to

define what it means to do a good job at surveillance. 

Intuitively, the purpose of surveillance is to return

information on a set of targets to some user or set of users. 

Performance at the surveillance task will depend on the 

information’s quantity, accuracy, importance and timeliness. 

As will be discussed, there are many variations on the 

general problem. To accommodate the diversity of

surveillance missions, we start with a very general, decisiontheoretic formulation of the overall goal: to maximize the 

utility of returned information over a defined interval. 

Like Massios et al. (2001), we characterize 

information value in the negative – i.e. in terms of the cost of

not having observed a target for a given interval rather than 

the benefit of having observed the target at a given time. 

Consider the example of maintaining surveillance over a set 

of buildings, any of which might catch fire at any time. 

Observing the building allows us to call the fire department

if necessary, and thus limit the amount of damage. The

longer we go without observing, the more likely it is that a 

fire will have occurred (though the probability may still be 

very small) and the more damage any such fire is likely to

have inflicted. Thus, the expected cost of not observing the 

building (and thus remaining ignorant of its state) for a given

interval depends on the fire’s probability and expected cost

of occurrence. Specifically, the expected cost of ignorance 

(ECI) for having not observed a target τ during the interval t1

to t2 is: 

ECI τ (t1, t2) = ∫

=

⋅ −

2

1

( ) cost( 2 )

t

t t

p t t t dt

where p(t) is probability density function for the occurrence 

of some cost-imposing event E (e.g. a fire breaking out) and

cost(d) is a function describing the expected cost imposed by

E as a function of the time from occurrence to intervention. 

In other words, the cost of ignorance is the sum, for all points 

in the interval, of the probability of the event occurring at 

that point

1 times the expected cost if it occurs at that point.

If more than one kind of event can occur at a target, and the

event-types are uncorrelated, the expected cost of ignorance 

is simply the sum of the ECI values for each. 

Over the course of a surveillance mission, an 

interval running from tstart to tend, expected cost accumulates 

at each target2

. If the target is never observed during that 

period, the total mission ECI for that target is determined by 

the above equation for ECI τ with t1=tstart and t2=tend. 

Otherwise, observations divide the target’s mission timeline

into a sequence of intervals I τ where the target’s total 

mission ECI equals the sum of ECIs for each interval. 

ECI τ-mission = ECI τ(tstart, tend) = ∑

τ I

i

start end ECI(i ,i )

 

1

 Here we assume expected detectability latency l0 = 0 and refer to

the time of occurrence of an event rather the time it becomes

detectable. Values of l0 > 0 can be accommodated by integrating

from max(0 , t1 - l0) rather than from t1. 2 Time tstart represents a reference start time at which costs begin

accruing. 
The effect of observation occurring at t2 is to reduce the 

maximum expected cost of an event occurring at t < t2 from

cost(tend – t) to cost (t2 –t). This reduces the total mission

ECI and also constrains its maximum. For example, cost(t)

may asymptote at $5M, corresponding in our example to the 

building burning to the ground. If, e.g., the building is

observed every 30 minutes and cost(30 minutes) is $1M, the 

ECI over the course of the mission for that target cannot

exceed $1M. 

With this way of determining the mission ECI for a 

target, the total mission ECI can be defined simply as the 

sum of mission ECIs for all surveillance targets. The 

performance of a surveillance algorithm in a given mission is 

thus measured by its success in minimizing this total 

expected cost. We define ECImax as the total mission ECI if 

no targets are observed during the course of a given mission

and ECI<method> as the total mission ECI resulting from an 

observation schedule generated by a particular method.

Thus: 

value<method> = ECImax – ECI<method> 

Modeling a Mission

The choice of what probability function and what cost

function to use to model ignorance cost at a given target

depends on the kind of cost-imposing event(s) that may 

occur there. Some events are once-only, meaning that we 

assume they can occur at most once during the course of a 

mission (e.g. theft of an item). Others can re-occur serially 

(e.g. a security gate left open which can be closed and then 

left open again) or in parallel (e.g. an individual entering an

area illegally). Event probability may vary with some 

regular event (e.g. rush hour, night time), contingent upon 

some other event (e.g. rain) or may remain constant. For the

work described here, we have assumed that all events are

once-only and that occurrence probability is constant

assuming no prior occurrence. Thus, the exponential 

function 1- e-at

 describes the probability that event E has 

occurred by time t (assuming the start of the mission tstart = 

0); its derivative yields the probability density function p(t)

= ae-at. 

The cost function combines a number of factors. 

Most important is how the physical process initiated by an 

event unfolds and how cost accrues as a result. For instance, 

a building fire may start out slowly, at some point begin 

increasing rapidly in intensity, then eventually taper off as 

flammable material runs out and the cost of the fire

approaches the total value of the building. This suggests an 

s-shaped cost function such as a sigmoid. Other factors

include the initial cost c0 of the event (e.g. from an explosion 

that causes a fire), the maximum cost m that may accrue

from an event (e.g. the cost of the building plus fire cleanup

costs), the expected intervention latency l1 (e.g. how much

time it takes firefighters to get to the site and put out the fire) 

and expected reporting latency l2 (e.g. how long it takes to

get in range to alert firefighters). The work described here 

assumes that all events are modeled using a sigmoid 

normalized to intercept the y-axis (cost) at c0 and to

asymptote at m. 

( ) 0 ( ) 1 0 1

2

cost( ) 1 2m c

e

d c k d l l  − 

 



 − + = + − + +

 

Multiplying the probability and cost functions with initialcost and latency factors factored out for simplicity (c0 = l1 = 

l2 = 0), we get the ECI equation below for evaluating the 

expected cost of not observing a specified target (associated 

with parameters a, k and m) during the interval t1 to t2 (each 

a displacement from the mission start time t0=0).3

ECI τ (t1, t2, a, k, m) = dt

e

ae m k t t

t

t t

at 1) 1

2 ( ( 2 )

2

1

− + − −

=

−

∫

From this framework, a clear process emerges for 

how a user can specify mission parameters, apply a 

surveillance decision method and then evaluate the output of

that method with respect to the mission. The first step is to

specify the mission. This involves defining a start/end

location, mission duration, surveillance vehicle (with range, 

kinematics, sensors and other characteristics) and set of

target locations. Each target is associated with one or more

events, and each event with parameterized probability 

density and cost functions. Given our previously described

assumptions about these functions, users would specify three 

parameters for each event: a, k and m. The value m is simply 

the maximum (asymptotic) cost of the event. To determine 

the probability rate parameter a, a user should specify some

reference probability interval for the event. For instance, the 

user may specify that the probability of the event is 0.2 

during a 60 minute interval. Solving for a yields the value 

.00372. To determine the cost rate parameter k, the user

should specify a reference cost interval such as $1M during

the first 30 minutes following occurrence. Solving for k

yields the value .0135. 

Second, after specifying all elements of the mission, 

this information is made available to the algorithm or person

responsible for generating a surveillance schedule. The 

algorithm or person’s output may take the form of a 

repeatable sequence that must be translated into a schedule. 

For example, the sequence ABCAB denotes that targets A, B

and C will be visited repeatedly and in order, skipping C on

alternate circuits and breaking off just in time to return to the 

start location before the mission end time. A schedule 

 

3 Though, we implemented a closed-form solution for the integral, 

we found that simple numeric approximation methods provide 

equivalent speed and accuracy. 
specifying at what times each target is observed over the 

course of the mission can be generated by simulation based 

on vehicle characteristics, weather and map information. 

The resulting schedule is then used to compute value<method>

as described in the previous section, providing a 

measurement of the expected benefit of performing 

surveillance using a given method. 

Comparative Evaluation Testbed

In the previous section, we addressed the question of how to 

measure the performance of a surveillance method in a given 

mission. The next step is to make it possible to compare 

different methods so as to learn their relative strengths and 

weaknesses. Such comparisons serve two important 

practical purposes. First, the process of developing and 

refining surveillance algorithms depends on knowing what 

weaknesses should be addressed and on being able to 

measure the effect of intended improvements. Second, this 

kind of analysis might allow a system to automatically select 

the best method for a newly defined mission by matching to 

the most appropriate method. 

 Comparative analysis requires testing surveillance 

methods against a set of significantly different mission types. 

This raises the question of what features are likely to 

differentially affect the performance of different methods. A 

set of such features would provide a basis for classifying 

missions into different types and thus for creating a stable 

testbed mission set. Unfortunately, it is not altogether clear 

which are important. It is not clear, for example, what 

features should be considered at all, what tradeoffs exist in 

the design of algorithms that are likely to impact sensitivity 

to a given feature and what features tend to vary significantly 

in missions arising in real operations. 

We have created an initial testbed mission set 

consisting of 243 missions based on 5 feature types 

(dimensions), each with 3 values. Feature types include: N, 

the number of targets to be observed, with possible values 4, 

8 and 16; spatial scale, representing the size of the map in 

which the mission takes place, with possible values .002, .02 

and 0.2 of the range of the vehicle; spatial distribution, the 

degree to which targets are clustered, with possible values of 

uniform, globular and 2-cluster; maxcost distribution, 

representing the variability across targets of the parameter m, 

with possible values of fixed, uniform, and 2-cluster; and 

cost rate distribution, the variability across targets of the 

cost rate parameter k,

4

 with possible values fixed, uniform, 

and 2-cluster. All missions use the mission modeling 

framework described above and all have the following 

features in common: mission duration is fixed at 60 minutes 

(the worst-case flight duration of our RMAX helicopter); 

 

4 Specific values of m are {10,20,30,40} with 30 used when 

maxcost distribution = fixed. Specific values of k are based on 

{20,40,60,80} minutes to reach .9 maxcost with 60 minutes used 

when cost rate distribution = fixed.

start/end point is located at the centroid of mission targets; 

the probability of occurrence of all events is fixed at .2 per 

hour; and initial cost (c0) = detection latency (l0) = response 

latency (l1) = reporting latency (l2) = 0. 

 Because we expect to enlarge and refine the testbed 

repeatedly as our understanding of user needs and algorithm 

design tradeoffs grows, we have created software that lets us 

easily create and modify testbeds, and run evaluation 

experiments with both algorithms and human subjects. The 

software includes a model of the flight characteristics of the 

RMAX, allowing us to accurately compute travel time 

between targets. This is likely to be especially important for 

evaluating the impact of spatial scale, particularly where 

targets are relatively near one another, since turn rate in 

aerodynamic flight, acceleration to cruise speed and other 

UAV characteristics are likely to have large and varying 

effects on travel time. 

Case Study: 2-opt vs. Human Performance

To illustrate the described evaluation framework, we 

describe its application to two surveillance methods. The 

first method is based on a 2-opt exchange algorithm (Reinelt 

1994) for the Traveling Salesman Problem (TSP). The 

algorithm has been modified in a number of ways in order to 

(a) generate a repeating cycle of visits that start and end on a 

given location but do not visit it in the interim and (b) make 

use of a flight dynamics model requiring that travel time 

between locations is not a constant, but instead varies with 

initial speed, initial turn angle and end turn angle. It is 

important to note that while these modifications make the 2-

opt algorithm applicable to our surveillance problem, any 

TSP-based approach is likely to perform well only in those 

parts of the space of possible missions where TSP-like 

assumptions hold – e.g. where there are fixed value 

distributions for cost-rate and maxcost. In general, we 

expect different algorithmic approaches to perform well in 

different parts of the mission space. 

 Second, we evaluated human-decision making in 

directing surveillance, the method corresponding to current 

practice. A human subject selected surveillance paths for 

each of the 243 mission scenarios in our testbed. Each 

mission was represented graphically as a map showing all 

relevant dimensions. Targets were represented as icons 

colored to indicate cost rate (urgency) and with shape varied 

to represent maximum cost (importance). The start/end 

(home) point was displayed as a distinctive icon and spatial 

scale as a circle centered on the home point whose radius 

represented .002 of the vehicle’s specified flight range. The 

subject used a mouse to select and modify a route and were 

allowed as much time as they wished on each mission. In 

contrast to the 2-opt method which always attempted to visit 

all targets, humans were allowed to exclude targets from the 

surveillance route if they wished. 
Pct. Adv. N Spatial

4 8 16

Scale Rate Cost 2-Cluster Globular Uniform 2-Cluster Globular Uniform 2-Cluster Globular Uniform

0.002 Fixed Fixed 0 0 0 0 14 0 6 31 -3

Clustered 000 0 16 5 7 29 7

Uniform 0 0 -1 42 24 5 2 10 10

Clustered Fixed 000 0 0 11 0 0 11

Clustered 000 000 0 0

Uniform 000 000 0 0

Uniform Fixed 143 47 0 130 19 47 10 93 4

Clustered 22 28 23 0 12 6 3 8 0

Uniform 61 20 -2 0 18 7 2 5 9

0.02 Fixed Fixed 000 110 0 1

Clustered 000 110 0 1

Uniform 000 110 1 2

Clustered Fixed 000 100 1 6

Clustered 000 100 0 9

Uniform 000 1 16 0 0 6 0

Uniform Fixed 000 100 2 2

Clustered 000 100 2 2

Uniform 000 100 0 2

0.2 Fixed Fixed 100 0 -1 0 -2 -22 4

Clustered 1 0 0 -1 5 -10 -6 -15 3

Uniform 0 0 -1 -2 4 -8 -5 -19 4

Clustered Fixed 000 8 0 14 9 -1

Clustered 000 9 -1 -11 11 -14 5

Uniform 0 0 -1 16 8 3 5 -10 4

Uniform Fixed 3 0 23 14 -7 22 2 -7 10

Clustered 16 0 23 9 -3 -12 9 -16 8

Uniform 23 0 31 15 4 2 -3 -26 5

1

1

7

0

0

0

0

1

0

1

1

10

Table 1. Percentage difference in performance between 2-opt and human-directed surveillance 

Our initial expectations were that performance 

would vary significantly between the methods based on

certain strengths and weaknesses. In particular, the 2-opt 

method, with a computer’s advantages in speed and

precision, would presumably do well on small scale maps

where aerodynamic factors would favor complex paths that 

minimize turn angle rather than (only) distance between 

targets. It would likely perform poorly on maps with varying

max-cost and rate parameters since it could not reason about

that information. Humans, with natural visual-spatial 

capabilities that exceed any computer-based technique, 

might perform well when targets are spatially grouped. And,

allowed to exclude targets from the surveillance schedule, 

people would likely perform well on maps where non-fixed

distributions of max-cost and rate make some targets worth

skipping and on large scale maps where the importance of

being selective is especially great. 

Table 1 shows data for all 243 missions. Data

entries represent the percentage difference in performance

between the two methods, with positive values indicating 2-

opt advantage and negative values human advantage. Values

outside the range -10% to 10% are in boldface to indicate

where the greatest differences in performance lie. 

Overall performance was comparable, with 2-opt 

doing 4.9% better on average. In the human best case, the

subject outperformed TSP by 26%, whereas the best 2-opt

case had a 146% advantage. The latter was almost certainly 

due to human error, as the mission in which it occurred was

similar to others where the subject performed well. This 

may indicate a phenomenon favoring algorithmic methods in

general: human tendency to err when making surveillance 

decisions. 

Across the five independent variables, scale and 

cost-distribution stood out as especially significant in 

differentiating human from 2-opt performance (standard

deviations of 6.3 and 5.6 respectively). In all 9 cases where 

humans outperformed 2-opt by at least 10%, scale was large 

(0.2). In 24 of 36 (66%) cases where 2-opt was better by at

least 10%, scale was small (.002). N was least significant 

(s.d. = 1.3), though 7 of the 9 cases with human advantage 

>= 10% were with N=16. The ability to exclude leastimportant targets is most likely to prove valuable in large 

scale maps with large numbers of targets. That human 

performance was best in those cases suggests that this ability 

was the principal human advantage. 

Contrary to expectations, 2-opt performed relatively 

well with non-fixed cost and rate distributions. It performed 

particularly well when the rate distribution was uniform,

performing at least 10% better in 24 cases. Human

advantage >= 10% occurred with uniform rate in 3 cases. 

Confirming prior expectations, human performance was

better in cases with spatial structure (globular and 2-cluster), 
especially when N was high – 7 cases with 10% advantage 

vs. 1 for 2-opt. This suggests a constraint on the conditions 

in which people will be able to judge which targets to 

exclude. 

 This comparative evaluation was intended only to 

test and illustrate our technique. In particular, the data on 

human-directed surveillance came from a pilot study 

involving only a single subject. Given the limits of our 

current data, we limit our interpretation of the results to the 

identification of general patterns that deserve further study. 

We are currently running human subjects in a new version of 

the experiment that incorporates training in effective 

surveillance decision-making and provides computational 

decision aids through the UAV control interface. The new 

data should provide a more reliable measure of human 

performance in a genuine operational context, and thus a 

better baseline against which algorithmic performance can be 

measured. 

Next Steps

As described in the first section, a practical and effective 

UAV-based surveillance capability requires efforts in three 

areas. The first is to develop means to evaluate and compare 

different surveillance methods. There are numerous ways to 

improve the presented approach. The mathematical 

framework should be extended to include more event types 

(e.g. sequentially reoccurring), more event features (e.g. 

detection latencies) and more diverse probability and cost 

functions. The mission testbed should be refined and 

extended to include additional features and a greater range of 

values for each feature type (e.g. N=100). And the whole 

framework should be extended to accommodate multiple 

surveillance agents including not only multiple UAVs, but 

also heterogeneous human and robotic observers. 

 The second area of work is to develop new and 

better surveillance algorithms, iteratively refining them 

based on comparative analyses of their strengths and 

weaknesses. A particularly important class of algorithms are 

those that make and/or modify surveillance decisions at 

execution-time in response to changing conditions (e.g. wind 

shifts, changes in user information needs). Though our 

framework has been described as a way to evaluate 

surveillance schedules prior to execution and without regard 

to such changes, it applies equally to post-hoc evaluation of 

schedules generated reactively (at execution-time) in 

response to unfolding events. As significant changes in 

physical conditions and user needs are likely to occur 

frequently in realistic missions, we anticipate that this 

framework will ultimately be more useful for evaluating 

reactive surveillance methods than for methods that schedule 

exclusively in advance. In particular, we anticipate applying 

it to assess ongoing scheduler enhancements to the 

Autonomous Rotorcraft Project helicopter’s mission-level 

autonomy component (Apex). 

 Finally, these approaches must be made “usable” in 

real operational contexts where limits on time, knowledge 

and user expertise are likely to constrain interactions with the 

surveillance agent. On issue of particular concern is to 

enable users without a background in decision-theory or 

mathematics to specify mission parameters. Though users 

may be experts in the operational domain, eliciting the 

required utility and probability knowledge from them is 

notoriously difficult, though useful techniques exist (French 

1986) and continue to emerge (Wang and Boutilier, 2003). 

Acknowledgements 

This work was supported by the NASA CICT / Intelligent 

Systems program. We thank Peter Cheeseman, Jeremy 

Frank, Roger Remington, Byron Roe, David Smith and 

Matthew Whalley for many useful discussions. 

References

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Surveillance Using the Hierarchical Structure of the 

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Reinelt, G. (1994) The Travelling Salesman. Computational 

Solutions for TSP Applications, volume 840 of Lecture Notes in 

Computer Science. Springer-Verlag, Berlin Heidelberg New 

York, 1994. 

Sacks, S. (2003) Evaluation of Police Patrol Patterns. Working 

papers 2003-17, University of Connecticut, Department of 

Economics. 

Whalley, M., Freed, M., Takahashi, M., Christian, D., PattersonHine, A., Schulein, G. and Harris R. (2003) The NASA/Army 

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Helicopter Society 59th Annual Forum. Phoenix, Arizona. 
1

INTELLIGENT AUTONOMY AND PERFORMANCE 

MEASURES FOR COORDINATED UNMANNED VEHICLES 

A. Scott Lewis+ and Lora G. Weiss++ +

 Research Associate, asl103@psu.edu ++Senior Research Associate, lgw@enterprise.arl.psu.edu 

Applied Research Laboratory/The Pennsylvania State University (ARL/PSU) 

State College, PA 

ABSTRACT 

This paper describes an autonomous Intelligent Controller (IC) 

architecture directly applicable to the design of unmanned 

autonomous vehicles and performance measures associated with 

intelligent autonomy. The vehicles may operate independently or 

cooperate to carry out complex missions involving disparate sensors 

or payload packages. An approach to measure the performance 

achieved with collaborative control is presented and simulation 

scenarios are provided to demonstrate how the metrics are applied. 

KEYWORDS: Emergent capability, collaborative control, 

intelligent control, unmanned vehicle, performance metrics

1. INTRODUCTION 

This paper describes an autonomous Intelligent Controller 

(IC) architecture directly applicable to the design of unmanned 

autonomous vehicles and collaboration and coordination 

between them. Two fundamental issues associated with 

multiple unmanned vehicle control are: how is collaboration 

enabled within the architecture and how is performance 

measured. This paper presents a behavior-based control 

approach for intelligent autonomy for a group of coordinated 

vehicles and it describes a metric for assessing collaborative 

performance. 

There are many variants of behavior-based architectures. 

One of the earliest was the subsumption architecture of 

Rodney Brooks1

. The basic concept is that the control system 

is constructed around a collection of largely independent 

operational capabilities referred to as behaviors or behaviorgenerating elements.2,3 Prototype designs of such systems 

have shown that the overall capability of a system can exceed 

that of more conventional architectures, and sometimes to a 

surprising degree. 

For multi-vehicle collaborative control, Chandler and 

Pachter4

 summarize research issues involved in autonomous 

control of tactical UAVs. They conclude that decision making 

through planning and management are the essence of the 

autonomous control problem, and they determine that 

hierarchical decomposition is a promising approach. 

Stipanovic et al.5

 use decentralized overlapping control 

for a formation of UAVs. The dynamic model of the 

formation with an overlapping information structure constraint 

is treated as an interconnecting system with overlapping 

subsystems. Their approach, though, does not enable dynamic 

reconfiguration or the ability to reconfigure the mission plan. 

Boskovic et al.6

 present a multi-layer control architecture 

for UAVs with four layers: (1) Fault-tolerant redundancy 

management, (2) Trajectory generation, (3) Path planning, and 

(4) Decision making. They propose a model switching method 

to address different failure scenarios. 

Measuring performance of groups of intelligent systems 

is a topic of recent interest. Jacoff et al7

 present performance 

metrics for urban search and rescue robots with emphasis on 

pertinent robot capabilities and different robotic 

implementations. Yang et al8

 use performance metrics in the 

development of a collision avoidance and warning system. 

Zadeh9

 has introduced the concept of machine IQ (MIQ) to 

measure the intelligence of smart machines. However, as a 

metric of intelligence, the MIQ is product specific and does 

not involve the same dimensions as the human IQ. It is 

relative and the MIQ of a camera made in 1990 would be a 

measure of its intelligence relative to cameras of the same era 

and would be much lower than the MIQ of cameras made 

today.10 

Several workshops on performance metrics for intelligent 

systems have been organized by the National Institute of 

Standards and Technology (NIST) and their results 

encapsulated in proceedings. Evans and Messina11 discuss 

challenges and issues in defining performance metrics for 

intelligent systems. They cite government agencies basing 

major programs on intelligent capabilities and emphasize that 

there is no consensus on how to define or measure an 

intelligent system. However, they summarize the traits that an 

intelligent controller might have including: adaptability, 

capability of learning, doing the right thing or acting 

appropriately, non-linearity, autonomous symbol 

interpretation, goal-oriented, and knowledge-based. 

An engineering perspective is given by Lee et al12 in 

which they present several questions that should be asked 

prior to the definition of the metric of system intelligence. 

Among those are (1) should the intelligence measure be goaldependent or goal-independent (2) should the intelligence 

measure be time-varying or time-invariant and (3) should the 

intelligence measure be resource-dependent or resourceindependent? DeLeo13 proposes measuring classifier 
2

intelligence by computing the area under the receiver 

operating characteristic (ROC) curve and using the concept of 

the separation index he introduces. Feddema et al. discuss 

their view of emergent behavior with regard to finite state 

machines14. 

Albus15 claims a barrier to the development of intelligent 

systems is the lack of metrics and quantifiable measures of 

performance and that there cannot be a science of intelligent 

systems without standard units of measurement. While the 

determination of performance metrics and measures with 

regard to physical entities is precisely defined and accepted, 

performance metrics and standards for intelligent systems are 

loosely defined and no acceptable standards exist. This paper 

presents an intelligent control architecture for collaborative 

control and an approach for measuring performance.

The Intelligent Controller (IC) described in this paper was 

initially based on the subsumption approach, but actual system 

needs presented more challenging requirements. This resulted 

in a newer, more novel approach to intelligent control 

architectures16, 17, 18 . 

Extending the IC architecture for collaborative behaviors 

also resulted in a unique approach for coordinated control. 

This resulted in the derivation of a measure of the 

performance gained by operating as a coordinated group of 

autonomous vehicles vs. a group of autonomous vehicles 

operating on their own accord. This metric is discussed in this 

paper and calculated for two scenarios. 

2. INTELLIGENT CONTROLLER (IC) 

ARCHITECTURE 

To appreciate the approach to measuring performance, 

one must understand the underlying architecture. This section 

provides the architecture used for collaborative control. The 

Intelligent Controller (IC) architecture developed at Penn 

State University’s Applied Research Lab (ARL/PSU) is 

composed of two main modules: Perception and Response. 

The Perception module is where sensor data is analyzed, 

information is integrated, and interpretation of the events is 

generated. The Response module is where the situation is 

assessed, plans are generated, and re-planning or plan 

execution occurs. Figure 1 illustrates the IC modules for a 

single controller. The responses from the Response module 

are in the form of commands and communications to vehicle 

subsystems or to external systems. These systems and 

subsystems may be other ICs, conventional control systems 

(effectors), or human collaborators. 

2.1 Perception Module 

The role of the Perception module is to create an internal 

representation of the external world relevant to the IC, using 

sensor data streams as inputs. A key capability of the 

Perception module is to make correct inferences and recognize 

the existence of properties in the representational objects (e.g., 

obstacles) from incomplete and potentially erroneous input 

data. The Perception module contains data fusion algorithms 

and Continuous Inference Networks (CINETs).19 CINETs are 

used to infer properties or events, such as "target" or "friend", 

by appropriately combining multiple pieces of information in 

an automatic recognition process. 

2.2 Response Module 

The role of the Response module is to plan and execute in 

real time a course of action to carry out a specific mission, 

given the situational awareness derived by the Perception 

module. The Response module is decomposed into three 

levels: A Mission Manager, Behaviors, and Actions. The 

Mission Manager retains the big picture and specifies a 

mission plan, which is a list of relevant Behaviors to be 

executed. Each Behavior has its own plan to execute, which is 

a list of Actions to be conducted. Control is cycled and 

interrupted appropriately using an Execution Engine within 

the Response module. The Execution Engine is an applicationindependent component of the Response module that calls the 

functions in the Response module in an appropriate order. 

Figure 2 illustrates components of the Response module for a 

UAV with a selected set of Behaviors (blue) and Actions 

(pink). 

Figure 1: High Level Decomposition for a Single IC. 

2.3 Multiple ICs 

Multiple ICs can be integrated in a hierarchy for 

coordinated control. Each IC retains the same architecture yet 

has a different local mission to execute (such as UAVs 

searching different local areas). This replication of 

architecture allows management of complexity and 

considerably simplifies the problem of designing multiple, 

interacting, intelligent controllers for complex systems. 

Just as a collection of Behaviors within an IC needs a 

Mission Manager for coordination and arbitration, a collection 

of ICs within a system also requires a supervisor. This role is 

SENSOR INPUTS

PAYLOAD INPUTS

Sensor 1

Sensor N

Messages

.

.

.

•Acoustic Contacts

•Radar Contacts

•Intel Information

•SIGINT/ELINT

•MCM Data

•In-Situ Environmental Data

•Orders

•Advice 

INTELLIGENT CONTROLLER

Perception Response

•Sensor Data Fusion

•Information Integration

•Inferencing and Interpretation 

•Situational Awareness

•Operational Assessment

•Dynamic Planning and Replanning

•Plan Execution

•Incoming Missile

•Mine field

•Water Characterization

•D/E Submarine

•Obstacle

•Acoustic Threat

•ELINT Threat

•Launch Long-range Missile

•Monitor Situation

Survey Minefield

Environmental Path Planning

Engage Target

Configure Team

Avoid Obstacle

Messages

Conventional

Control

Systems

Human 

Collaborator

Other 

Autonomous

Controllers

SENSOR INPUTS

PAYLOAD INPUTS

Sensor 1

Sensor N

Messages

.

.

.

•Acoustic Contacts

•Radar Contacts

•Intel Information

•SIGINT/ELINT

•MCM Data

•In-Situ Environmental Data

•Orders

•Advice 

INTELLIGENT CONTROLLER

Perception Response

•Sensor Data Fusion

•Information Integration

•Inferencing and Interpretation 

•Situational Awareness

•Operational Assessment

•Dynamic Planning and Replanning

•Plan Execution

•Incoming Missile

•Mine field

•Water Characterization

•D/E Submarine

•Obstacle

•Acoustic Threat

•ELINT Threat

•Launch Long-range Missile

•Monitor Situation

Survey Minefield

Environmental Path Planning

Engage Target

Configure Team

Avoid Obstacle

Messages

Conventional

Control

Systems

Human 

Collaborator

Other 

Autonomous

Controllers

SENSOR INPUTS

PAYLOAD INPUTS

Sensor 1

Sensor N

Messages

.

.

.

•Acoustic Contacts

•Radar Contacts

•Intel Information

•SIGINT/ELINT

•MCM Data

•In-Situ Environmental Data

•Orders

•Advice 

INTELLIGENT CONTROLLER

Perception Response

•Sensor Data Fusion

•Information Integration

•Inferencing and Interpretation 

•Situational Awareness

•Operational Assessment

•Dynamic Planning and Replanning

•Plan Execution

•Incoming Missile

•Mine field

•Water Characterization

•D/E Submarine

•Obstacle

•Acoustic Threat

•ELINT Threat

•Launch Long-range Missile

•Monitor Situation

Survey Minefield

Environmental Path Planning

Engage Target

Configure Team

Avoid Obstacle

Messages

Conventional

Control

Systems

Human 

Collaborator

Other 

Autonomous

Controllers

SENSOR INPUTS

PAYLOAD INPUTS

Sensor 1

Sensor N

Messages

.

.

.

•Acoustic Contacts

•Radar Contacts

•Intel Information

•SIGINT/ELINT

•MCM Data

•In-Situ Environmental Data

•Orders

•Advice 

INTELLIGENT CONTROLLER

Perception Response

•Sensor Data Fusion

•Information Integration

•Inferencing and Interpretation 

•Situational Awareness

•Operational Assessment

•Dynamic Planning and Replanning

•Plan Execution

•Incoming Missile

•Mine field

•Water Characterization

•D/E Submarine

•Obstacle

•Acoustic Threat

•ELINT Threat

•Launch Long-range Missile

•Monitor Situation

Survey Minefield

Environmental Path Planning

Engage Target

Configure Team

Avoid Obstacle

Messages

Conventional

Control

Systems

Human 

Collaborator

Other 

Autonomous

Controllers
3

assumed by a Supervisory IC. Multiple ICs may also exist 

within a single vehicle in this hierarchical architecture, as 

determined by design decisions. Figure 3 depicts how multiple 

ICs communicate. 

For multiple vehicles, a significant portion of a mission 

may be achieved by having the capability of the individual 

autonomous units carry out their own tasks while operating in 

a group. Given that the individual vehicles are intelligent and 

capable of inferring the behavior of other cooperating vehicles 

through sensing and observation, only a limited number of 

direct communications may be necessary to achieve 

significant performance enhancements. 

The overall capability of the aggregate system is then an 

emergent property stemming from the collaboration among 

individual vehicles coupled with their own abilities to carry 

out autonomous operations over a range of variations in the 

missions. For a properly designed collaborative unmanned 

vehicle system, this emergent capability is greater than that of 

a system composed of vehicles acting alone. 

 

Figure 2. Sample Elements of Response Module. 

Figure 3. Architecture for Multiple IC Communications. 

3. SYSTEMS OF ICs 

 The capability of a single IC is the aggregate of the 

capabilities of its modules. In particular, its operational 

capability is determined by the aggregate of its Behaviors. To 

expand the scope of its operational capability, a Behavior is 

simply added. To remove a capability, a Behavior is removed, 

which will not affect operation of the remaining Behaviors. 

 This approach can be extended to a group of ICs, where 

the architectural relationship between the Mission Manager 

and its set of Behaviors is replicated to define the relationship 

between a Supervisor IC and the set of vehicle ICs under its 

supervision. Figure 3 illustrates this extended Architecture. 

The hierarchy can be expanded arbitrarily in horizontal and 

vertical directions. 

3.1 Communications

 In contrast to the internal communication paths of 

Response, communication between one IC on a vehicle and 

another IC on a separate vehicle may not be possible at a 

given time due to the characteristics of the external medium. 

Consequently, the architecture supports both peer-to-peer 

communications and peer-to-supervisor communications. 

 Permitted message types for peer-to-peer (and peer-tosupervisor) communications are Sensor-data, ExternalAdvisories, and Queries. Sensor data passed among ICs serves 

to extend the senses of the receiving IC and consequently 

potentially improves its performance. Bandwidth limitations 

imposed by the external medium may require that the 

communicated data be in highly processed form for sufficient 

compactness. External-Advisories may be used by an IC to 

inform partners within communication range of its operational 

status or its interpretation of its local environment. Queries 

may be sent by an IC to its partners asking for information it 

needs that they may be able to provide. 

 There is no requirement that all ICs understand exactly 

the same language; messages containing Words that are not 

understood by the Perception processing of the receiving IC 

may simply be ignored or routed through a central unit that 

may serve as a translator. 

3.2 Collaborative Operations 

 The operating characteristics of a group of autonomous, 

coordinated controllers constitutes an autonomous intelligent 

control system, and their design based on this architecture can 

be summarized as follows. The autonomous system is 

composed of one or more ICs, where one of the ICs may 

possibly be a supervisor ICs. Each IC’s objective is to carry 

out a local mission but in coordination with the global mission 

and defined by the set of Orders for the collective system. 

These Orders may be altered during mission execution by 

receipt of new Orders from a human or a Supervisor IC. 

Within the constraints of its current Orders and its design, 

each IC is operating autonomously. There does not exist an 

"optimal control law" for the system of ICs, and the designers 

do not attempt to derive one. 

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data Peer-to-Peer

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data Peer-to-Peer

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data Peer-to-Peer

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data

HUMAN

GUI

Messages

Messages

Messages

Messages

Effector

Commands

Smart

Sensor

Data

Messages

Effector

Commands

Effector

Commands

PERCEPTION RESPONSE

Task 1

Intelligent Controller

PERCEPTION RESPONSE

Task 2

Intelligent Controller

PERCEPTION RESPONSE

Supervisor Intelligent Controller

Smart

Sensor

Data

Messages

Smart

Sensor

Data Peer-to-Peer
4

 Rather, the objective in the design of each IC is for it to 

be able to operate “optimally” as an individual, given its 

current set of Orders and its perceived world as created by its 

Perception processing. This perceived world may include a 

Representational Class, say “Partner,” where an instance of 

“Partner” represents the status of a partner or peer, including 

its operational plans and objectives to the extent known. This 

knowledge will generally be incomplete and changeable. 

 An autonomous intelligent control system such as this 

would appear to constitute a close parallel to biological 

systems such as beehives, ant colonies, and football teams. 

The system is composed of a collection of individuals with 

certain specialized characteristics and with some ability to 

communicate with each other. Operating together, the 

resulting system can have emergent properties, strengths, and 

survivability that go beyond the sum of that of the individual 

units. 

 The IC architecture also supports collaborative control of 

heterogeneous vehicles with varying architectures and levels 

of autonomy. This is accomplished by developing standard 

interfaces for communications and by providing the level of 

capability of each vehicle to the other vehicles through a 

database, where the database is accessed to determine the 

capabilities of the other vehicles before issuing 

4. MEASURING EMERGENT 

COLLABORATIVE CAPABILITIES 

4.1 The Collaborative Gain Metric 

Collaborative gains result from the communication 

between platforms, where exchange and interpretation of 

information is crucial, and from coordinated mission control. 

Collaboration involves interpretive and behavioral adaptation 

among the platforms as a result of integrating communicated 

data into the internal representations of the central system. 

Multi-platform collaboration should increase the 

likelihood of achieving mission objectives of the system over 

and above that achievable by a base capability. However, a 

collaborative gain is not automatically positive, since it is 

possible to design a system in which the communication and 

collaboration results in conflicts, causing deterioration in the 

system’s ability to perform its mission. 

One approach to evaluating the collaborative contribution 

of a system involves defining an index to measure the 

collaborative gain (CG ) of this system. One such metric is: 

∑=

=

M

i

CG i iTi

1

α β , (1) 

whereα i is a weight reflecting the importance of the task to 

the overall mission, β i denotes the success (0 or 1) of the task, 

andTi is the i

th of M mission tasks. The goal is to maximize 

the CG. 

For example, consider two UAVs, A and B, that are 

similarly capable of identifying a target. Assume platforms A's 

target has a higher priority and that A has been damaged and 

incapable of fulfilling its top priority. If B is about to identify 

its target but has only enough fuel to identify platform A's 

target, its priority will be reconfigured so that its original 

target will be ignored and its new target will be that originally 

assigned to A. Based on the extent of damage to A, platform A 

might be reassigned to another lower priority task. This type 

of cooperation leads to controlled emergent behavior, but 

mathematically quantifying it is an open task. By changing 

B’s target, then β i for A is 1 instead of 0 resulting in a higher 

CG. 

 In cases where it is possible to measure partial success of 

an unmanned vehicle accomplishing its mission, the value of 

β i becomes a variable, i.e., 

0 ≤ β i ≤1 (2) 

This allows partial success of an individual UAV or group of 

UAVs to be captured within the context of this same measure. 

4.2 Multiple, Coordinated UAV Control and Evaluation 

Controllers based on the IC architecture have been 

designed for multiple UAVs capable of executing an 

individual mission and collaborating with other UAVs to 

execute a larger, overall mission. Performance of one such 

design is described below. 

For this collection of UAVs, the functional capabilities of 

the prototype group include Navigation, Avoidance, Search, 

Investigate, Attack, Assist, Communicate, and Supervise. 

Each of these operations is implemented as an independent 

Behavior that operates autonomously within its scope, where 

each conducts real-time planning and analysis of the situation 

relative to mission execution, and each responds appropriately 

to the results of that analysis. 

Each behavior has one or more Actions that are responsible 

for carrying out sub-operations and reacting directly to objects 

of interest as represented in the Perception module. These 

reactions consist of commands to vehicle subsystems such as 

an autopilot or sensor control system. 

The initial UAV controllers developed are actual 

controllers operating closed-loop in a virtual environment 

consisting of a simulation of the external world and vehicle 

subsystems. These simulated subsystems include an assumed 

set of sensor systems, effector systems (e.g., an autopilot or 

other conventional control systems), vehicle dynamics, and 

interfaces. This closed-loop operation, in which actual 

controllers are stimulated with synthetic data, allows for issues 

to be addressed that are indicative of those expected to be 

encountered by a collaborating group of UAVs. 

Multi-UAV control was exercised and evaluated by using 

a simulation of the external environment and vehicle 

subsystems, including assumed sensing systems for 

navigation, avoidance, and target detection. The simulation 
5

stimulated the actual controllers. The operational functionality 

of the prototype collaborative UAV control capabilities was 

exercised in various scenarios during the design process. Two 

of these scenarios are described below. 

Figure 4: Screen Capture of Three UAVs Collaborating to 

Search and Attack Large and Small Targets. 

Scenario 1: A screen capture of the first scenario is presented 

in Figure 4. In this scenario, three UAVs are provided search 

areas (red boxes) with the objective being to attack large and 

small targets. The UAVs are authorized to attack large targets 

(tanks) without independent target confirmation. However, 

they are required to obtain independent target confirmation 

prior to attacking small targets (jeeps). Included in this 

scenario are way points (x) and an obstacle (large circle), so 

that the Navigation and Avoidance behaviors are activated. 

Also in this scenario, towards the end of the overall mission, 

UAV #1 is shot down before completing its mission. The 

other UAVs re-plan their missions to ensure the mission of 

UAV #1 is completed even after it has been removed from the 

engagement. Such a scenario allows evaluation of the 

collaborative capability of the multiple UAVs to execute the 

overall mission of clearing out targets in the specified area. 

The performance associated with this scenario can be 

captured in the Collaborative Gain metric given by equation 

(1). If the gain is measured by individual UAV success, and 

where α i , β i , and Ti are associated with UAV #i, i=1,2,3, 

then the performance of the individuals is given by summing 

the success of each individual unit accomplishing its mission. 

In this example, for the individual performances, 

α i = 1, i = 1,2,3 

β1 = 0, β2 = 1, β3 = 1 

so that without collaboration, the performance of the units is 

given by: 

CG = 2.

If partial success is allowed to be measured (e.g., using 

equation (2)), then 

β1 ~ .42, 

where β1 includes the success of eliminating the targets 

(highest priority that had a 0.833 success rate) followed by 

successfully returning to a rendevous point for updates (lower 

priority with 0 success). Thus, the performance of the 

individual UAVs is given by 

CG ~ 2.42. 

When the UAVs are allowed to cooperate to execute the 

mission, UAV #2 completes the mission of UAV #1, so that 

β1 = 1 

and 

CG = 3. 

Thus, enabling collaboration between the units provides a 

level of payoff in mission success.

Scenario 2: As another example of the coordinated control, 

one of the evaluation scenarios evolved as follows: Five 

UAVs were collaborating. UAV #1 was designated as the 

supervisor and delegated missions (search areas and 

rendezvous points) to the five individual UAVs. See Figure 5. 

During the course of operations, UAVs #2, #4, and #5 crash, 

and UAVs #1 and #3 return to a rendezvous point. The 

supervisor UAV requests the status of individual UAVs and 

reassigns the search areas of the downed UAVs to itself (UAV 

#1) and to UAV #3. See Figure 6. To further demonstrate the 

collaboration, the scenario then has UAV #3 go down. When 

the supervisor returns to the rendezvous point and identifies 

that UAV #3 is unresponsive, it re-plans and searches the area 

that UAV #3 was responsible for, and it completes the overall 

mission. 

The performance associated with this scenario can also be 

captured in the Collaborative Gain metric given by equation 

(1). If the gain is measured by individual UAV success, and 

where αi, βi, and Ti are associated with UAV #i, i=1,..,5, then 

the performance of the individuals is given by summing the 

success of each individual unit accomplishing its mission. In 

this example, for the individual performances, 

α i = 1, i = 1,...,5 

β1 = β 3 = 1 

β i = 0, i=2 ,4, 5 

so that without collaboration, the performance of the units is 

given by: 
6

CG = 2. 

If partial success is incorporated into this metric, the 

performance will be slightly higher, but not as high as for 

cooperating units. When the units are allowed to cooperate to 

execute the mission, UAV #1 completes the mission of the 

other UAVs, so that 

β i = 1, i=1,...,5 

and 

CG = 5. 

Again, enabling collaboration between the units provides a 

level of payoff in mission success. 

Figure 5: Screen Capture of Five Collaborating UAVs and 

Their Assigned Search Areas. 

5. CONCLUSIONS 

ARL/PSU’s experience in unmanned vehicles lead to the 

development of a unique, robust, universal architecture for the 

design of intelligent autonomous vehicles. This IC 

architecture provides a reliable approach to the design of a 

single unmanned vehicle or of a system of autonomous 

intelligent units that collaborate with each other and with 

humans to carry out complex missions. 

 When this high level of intelligent autonomy is integrated 

into a system of collaborating, unmanned vehicles, an even 

larger gain results. This gain is measured with the quantity 

called Collaborative Gain. Examples indicate that the 

performance of collaborating units can exceed that of 

individual units operating on their own accord, and the 

improvements can be significant. 

Figure 6: Screen Capture of Two Collaborating UAVs 

Completing the Missions of Three Downed UAVs. 

6. ACKNOWLEDGEMENTS 

 The authors would like to acknowledge several 

researchers at Penn State’s Applied Research Laboratory, 

including M. Roeckel, J. Stover, S. Neal, J. Miller, and C. 

Walker. 

7. REFERENCES 

1. Brooks, R.A., "Intelligence Without Representation, 

"Artificial Intelligence," 47, pp. 139-159, 1991.

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21, No. 3, pp. 473-509, 1991. 

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Control Architecture with Application to Coordination of 

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1998, pp. 394-398. 

5. Stipanovic, D. M., Inalhan, G., Teo, R. and C.J. Tomlin, 

Proc. of the 41st IEEE Conference on Decision and Control 

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of the American Control Conference, 2002, Vol.: 3, 8-10 

May 2002, pp. 1825-1830. 

7. Jacoff, A., Messina, E., Weiss, B. A., Tadokoro, S. and Y. 

Nakagowa, Proceedings of the 2003 IEEE International 

Conference on Intelligent Robots and Systems, Las Vegas, 

Nevada, October 2003, pp. 3396-3403. 

8. Yang, L., Yang, J.H., Feron, E., and V. Kulkarni, 

Proceedings of the Intelligent Vehicles Symposium, June 9-

11, 2003, pp. 316-321. 
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9. Zadeh, L. A., "Fuzzy Logic, Neural Networks, and Soft 

Computing," Communications of the ACM, 37 (3), pp. 77-

84, 1994. 

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Critical View," Proceedings of the 2000 PerMIS Workshop, 

pp. 105-111, Aug. 14-16, 2000, Gaithersburg, MD. 

11. Evans, J. M. and E.R. Messina, "Performance Metrics for 

Intelligent Systems," Proceedings of the 2000 PerMIS 

Workshop, pp. 101-104, Aug. 14-16, 2000, Gaithersburg, 

MD. 

12. Lee, S., Bang, W. C. and Z.Z. Bien, "Measure of System 

Intelligence: An Engineering. Perspective," Proceedings of 

the 2000 PerMIS Wksp., pp. 112-117, Aug. 14-16, 2000, 

Maryland. 

13. DeLeo, J., "Measuring Classifier Intelligence, Measuring 

the Performance and Intelligence of Systems," Proceedings 

of the 2002 PerMIS Workshop, pp. 26-31, Aug. 13-15, 

2002. 

14. Feddema, J. T., Robinett, R. D., and B.J. Driessen, 

"Designing Stable Finite State Machine Behaviors Using 

Phase Plane Analysis and Variable Structure Control," 

Journal of Intelligent and Robotic Systems, No. 36, pp. 349-

370, 2003 

15. Albus, J.S., "Metrics & Performance Measures for 

Intelligent Unmanned Ground Vehicles,” Proceedings of the 

2002 PerMIS Workshop., pp. 61-68, Aug., 2002. 

16. Stover, J. A. and R.E. Gibson, "Modeling Confusion for 

Autonomous Systems," SPIE, Science Artificial Neural 

Networks, 1710, pp. 547-555, 1992. 

17. Stover, J. A. and R.E. Gibson,"Controller for Autonomous 

Device", US Patent #5,642,467, Issued June 1997. 

18. Stover, J. A. and R.E. Gibson, “PIC 95 Project Report,” 

Tech. Mem. #00-128, Applied Research Lab., Penn. State 

Univ., State College, PA, Feb. 2002 

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Architecture for Autonomous Multisensor Data Fusion," 

IEEE Transactions on Industrial Electronics, 43, pp. 403-

410, 1996. 
Traversable Terrain Modeling and Performance 

Measurement of Mobile Robots

A. Shirkhodaie, R. Amrani, N. Chawla, and Vicks, T. 

Intelligent Tactical Mobility Research Laboratory 

Department of Mechanical and Manufacturing Engineering 

Tennessee State University 

3500 John Merritt Blvd., Nashville, TN 37209 

 

ABSTRACT

In this paper, we have described a technique for terrain traversability 

assessment modeling of mobile robots operating in natural terrain 

and presented a fast near-optimum algorithm for autonomous 

navigational path planning of mobile robots in rough terrain 

environments. The proposed method is based on visual sensing of 

terrain salient features and analysis of geo-location coordinates of the 

salient features. Using an algorithmic image processing technique, 

both free and obstacles spaces are differentiated and multiple 

candidate terrain paths are generated for optimization of trajectory 

terrain path of the robot. The algorithm uses a fuzzy logic terrain 

classifier to categories different salient features of the terrain. A 

virtual simulation is developed for terrain perception modeling and 

verification of generated trajectory path plans of the robot. The 

developed path-planning algorithm is computationally efficient, and 

suitable for implementation onboard autonomous robotic systems. 

Several different terrain conditions have been tested to validate the 

proposed approach. 

KEYWORDS: Traversable Terrain Modeling, Visual Path 

Planning, Autonomous Robots, Measure of Performance 

1. INTRODUCTION 

Autonomous navigation of outdoor terrain in an active pursuit 

of department of defense in battlefield reconnaissance and 

surveillance military operations and NASA in exploration of 

remote planetary surfaces by robotic rovers. There are a 

number of challenging issues with outdoor terrain navigation. 

A robot must have the ability to operation autonomously and 

intelligently on unstructured terrain with minimal interaction 

with remote human operators. Robot navigation system must 

provide sufficient onboard intelligence for long-range traverse 

in sanding, muddy, rocky, and poorly structured natural 

terrain, without jeopardizing the robot health and mission 

failure. 

This paper focuses, in particular, on the terrain visual sensing 

and terrain salient features recognition and characterization. 

We have described a method for terrain salient features 

detection using imaging technique and proposed a method for 

terrain rocks formation modeling. Furthermore, we have 

presented a method for near optimum visual path planning of 

mobile robots in natural terrain similar to the planet Mars 

surface. Section 2 addresses some of the challenges with 

terrain navigation. Section 3 presents a method for visual 

terrain sensing and salient feature extraction and recognition. 

Section 4 discusses a near optimum method for navigation 

path planning of the robot. Section 5 presents our 

experimental setup. Finally, section 6 presents the conclusion 

of this research effort. 

2. TERRAIN NAVIGATION 

Robot navigation in natural terrain is challenging due to 

uncertainty in recognition of salient features of the 

environment. Natural terrain is deceiving, superficial, and 

complex. Without a good perception model of the 

environment, a robot cannot reliably navigate a terrain and 

traverse to its goal successfully. Terrain traversability and 

path planning of all-terrain robots have been addressed by a 

number of researchers. Howard et. al., [1] presented a 

technique for terrain traversability assessment learning for 

outdoor mobile robot navigating. Using human-embedded 

logic in real-time, they demonstrated a technique for 

development of terrain perception based on features extracted 

from imagery data. In their method, they introduced a fuzzy 

logic framework and vision algorithms for analysis of terrain. 

Golda et. al., [2] presented a probabilistic modeling technique 

suitable for analysis of high-speed rough-terrain mobile 

robots. They have experimentally shown that their model can 

accurately predict robot performance in simple, well-known 

terrain, however, in unstructured environment, their stochastic 

method performance was degraded. A combination of terrain 

complexity and unaccountable uncertainty measures were 

found as leading causes in degradation of their predictive 

terrain assessment model. 

For long-range terrain navigation, accurate maps of the terrain 

are critical for robot navigation system. Without such maps, a 

robot may spend much time and energy venturing along what 

turns out to be a dead end. Olson et. al. [4] developed a 

method based on visual terrain mapping of Mars rovers. 

Using a visual stereo imaging fusion technique, they have 

demonstrated a reliable method for high fidelity terrain 

mapping and robot world perception modeling. By compiling 

terrain map images using a system that unified multiresolution models, they were able to integrate Mars descent 

and orbital images to obtain 3D terrain maps used by rovers 

for navigational purposes. 
Autonomous robot navigation in natural terrain can be divided 

into three closely related tasks: (1) Route Planning, (2) 

Navigation Planning, and (3) Mobility Planning. As 

illustrated in Figure 1, in Route Planning, objective is that of 

assessment of the terrain in bulk from a large distance away 

and deciding on feasible terrain courses that maximize 

traversability potential of the robot as well as its safety and 

health. Another objective is to identify pertinent intermediate 

landmarks. The landmarks are used as waypoints that robot 

can easily identify along its path and localize itself with 

respect to them if necessary. A typical route path plan may 

consist of many waypoints laid out on either an aerial map or a 

landscape image captured from a ground level, or a series of 

global position coordinates defined manually. Typical range 

of applicability of route planning ranges from 10 to 1000’s 

feet or higher. 

Navigation planning, on the other hand, can be considered as 

localization of obstacles, treacherous, hills, and slopes, 

positive and negative objects. Typical range of applicability 

of navigational planning varies from 2 to 12 feet for a slow 

moving robot and to a higher range for a fast speed robot. In 

navigation planning a set of short traverse path segments from 

current robot location to next intermediate landmark or the 

goal are decided. Navigational planning and following are 

coupled and achieved by means of a map or some model of 

environment. Localization and navigational error recovery is 

critical at this phase, in order to keep the robot as close as 

possible to its designated path or model frame of reference 

between its intermediate landmarks. Due to loss of 

environmental details in the field of view, navigational 

certainty in correct recognition of landmarks tends to diminish 

with the distance of landmarks from the robot. To keep the 

navigational certainty under control, typically the range of 

effectiveness of localization is within a few feet radius from 

the robot. Depending on the navigational speed of the robot, 

terrain intricacy, and sensory reliability, this range can be 

adjusted appropriately. 

The purpose of Mobility planning is that of describing a set of 

low-level drive actions that moves the robot through its 

obstacle terrain while negotiating and/or avoiding obstacles 

along its path. An important consideration in this phase is the 

dynamic interaction of the robot with its environment, in 

particular, detection of robot wheel traction losses during 

steering while avoiding wheel traps, wheel supports, and tip 

over states [6]. Another consideration is optimization of 

robot’s safety, energy, and reliability [5]. Typical range of 

applicability of mobility planning is from a few inches to a 

few feet depending on physical ability (i.e., wheel diameter) of 

the robot, and complexity of the terrain. In [6], dynamic 

modeling of robot and environment is shown reliable for 

simple, well-characterized terrain. However, on rough 

terrain, unknown terrain, model fidelity degrades due to 

imprecise knowledge of terrain parameters. 

For terrain navigation, it is very difficult if not possible to 

obtain a precise mathematical model of the robot's interaction 

with its environment. Even if the dynamics of the robot itself 

can be described analytically, the environment and its 

interaction with the robot through sensors and actuators are 

difficult to capture in a mathematical sense. The lack of 

precise and complete knowledge about the environment limits 

the applicability of conventional control system to the domain 

of autonomous robotics. If one draws an analogy to 

navigational skills of animals and humans in nature terrain, 

they both perform route, navigation, and mobility planning 

simultaneously and intelligently without getting trapped in the 

middle of terrain obstacles. Vision plays the most critical role, 

though physical mobility ability plays an equal important role 

in achieving navigational mobility objective. This observation 

motivated what it follows here. In this paper, we have 

presented an approach that solely relies on visual terrain 

characterization and intelligent path planning based on 

localization of salient features of the environment. 

Figure 1. Three Stages of Navigational Path Planning in Natural Terrain

1. Obstacle Rocks Localization

2. Impassable Zones Isolation

3. Target Identification 

4. Alternative Waypoints Generation 

5. Near Optimum Path Plan Generation

6. Absolute Path Updating

Route Planning Navigation Planning Mobility Planning

1. Terrain Assessment

• Rocky, Sandy, Pebbled

• Hilly, Flat, Mixed

• Rocks Formation, Density, Distribution 

• Traversable, Impassable 

2. Landmarks Generation & Tracking

3. Alternative Routes Selection

Range: 10-100’s ft Range: 3-12 ft Range: 2-4 ft

1. Environment Sensing and Interaction Control 

2. Safe Obstacle Negotiation

3. Nearby Obstacle Avoidance 

4. Steering and Skidding 

Control

5. Localization Via Landmarks

1.

2.

3.

1.

•

•

•

- - Range: -

1.

6. Absolute Path Updating

Figure 1. Three Stages of Navigational Path Planning in Natural Terrain

1. Obstacle Rocks Localization

2. Impassable Zones Isolation

3. Target Identification 

4. Alternative Waypoints Generation 

5. Near Optimum Path Plan Generation

6. Absolute Path Updating

Route Planning Navigation Planning Mobility Planning

1. Terrain Assessment

• Rocky, Sandy, Pebbled

• Hilly, Flat, Mixed

• Rocks Formation, Density, Distribution 

• Traversable, Impassable 

2. Landmarks Generation & Tracking

3. Alternative Routes Selection

Range: 10-100’s ft Range: 3-12 ft Range: 2-4 ft

1. Environment Sensing and Interaction Control 

2. Safe Obstacle Negotiation

3. Nearby Obstacle Avoidance 

4. Steering and Skidding 

Control

5. Localization Via Landmarks

1.

2.

3.

1.

•

•

•

- - Range: -

1.

6. Absolute Path Updating
3. TERRAIN PATH PLANNING 

The proposed visual navigational path-planning scheme is 

comprised of three phases. In the first phase, an image of 

natural terrain is obtained for detection of salient features of 

the environment. Using imaging techniques, the salient 

features are isolated and characterized. The environment 

features we are interested about include: obstacle free areas, 

rocks formations, sand piles, hills, and slopes. By salient 

features analysis, we can determine measures characterizing 

the environment surroundings and classify them appropriately. 

Furthermore, additional information such as rocks density and 

geolocation distribution, instable sand piles, and high risks 

ground conditions (i.e., hills, and slopes) for mobility can be 

discovered and avoided during navigational path planning of 

the mobile robot. In the second phase, our algorithm 

generates a number of waypoints that mark out a near 

optimum traversable trajectory path for the robot to follow 

toward its specified target location. In the last phase, a virtual 

model of the terrain is constructed based on geo-location 

coordinates and physical attributes of the salient features of 

the environment. The terrain model serves the robot as a 

reference model that embeds the robot's state of perception of 

its surroundings. The terrain model is applicable for 

simulation verification of robot's generated path plans; in 

particular, it is appropriate to give the operator tele-presence 

sense of robot's situation in the remote terrain. Figure 2 

presents an example of a rough terrain that our algorithm has 

analyzed along with the salient features that it has 

characterized. It also shows a generated world perception 

model of the rough terrain. The followings present details of 

this visual terrain traversability assessment technique. 

Initially, we divide an image of terrain captured by the robot 

into a matrix of smaller sub-windows and apply an adaptive 

binarization technique on each sub-window. This adaptive 

binarization method locally selects an optimum threshold for 

binarizing of each sub-window. The resultant binary image is 

a nonlinear map of geo-location of obstacles in the image 

frame and thresholds small rocks that are of insignificant size 

from the background. We explained the non-linearity issue of 

obstacles geo-location map in next paragraph. The resultant 

image can now be thought of a binary image where center of 

each black pixel represents the location of the obstacle centers 

in the original image. Next, a weight factor is assigned to 

each black pixels of the resultant binary image. By 

convoluting the compressed binary image, each black blob 

cell corresponds to an obstacle center is assigned a weight 

proportional on number of black blob cells surrounding it. 

This operation results obstacles appearing farther away from 

central obstacle receive less or equal weight depending on 

number of obstacle cell surrounding it. The result of this 

convolution operation is a hilly field map of the terrain 

environment. Note that obstacles relative gap from one 

another in the image frame is not linear. This is due to the fact 

that obstacles farther away from camera appear compressed in 

the depth of view. The depth perception diminishes rather 

with the square distance of obstacle from the camera. This 

fact is obvious by observation of Figure 2a. Much wider area 

of terrain is apparent in the upper part of image than in the 

lower part of image. Prior to analysis of the image field map, 

therefore, we map image coordinates of each sub-window to 

the 3D world coordinate using a camera calibration method 

described in [7]. 

Next, we apply a generic algorithm to obtain a free path for 

the robot among the obstacles. In the generic algorithm, size 

of the robot is assumed the same size as the width of diagonal 

distance of terrain area covered by the sub-window in the 

bottom row of the obstacle geo-location map. Note that 

physical area represented by image sub-window at upper rows 

is greater than that of image sub-window at the first row. The 

generic algorithm is a fast divide-and-conquer approach that 

searches the obstacle geo-location map row by row. It starts at 

a row above the first row and at the column where the robot is 

located. In that row, it searches left and right free spaces to 

the robot and measures a risk factor for each free space that is 

proportional to summation of obstacle centers around it. The 

algorithm determines the most suitable waypoint that 

minimizes the traveling distance of the robot progressively 

from start to goal. In an essence, it finds the safest waypoint 

in the current row that is closest to a straight path connecting 

the position of the robot to its desirable target location. This 

optimization method further attempts to intelligently choose a 

waypoint that is away from any major obstacle along its path. 

The multi-valued optimization process is carried out layer-bylayer and at each layer through this process a new waypoint is 

designated for the robot to follow. 

Navigation planning is crucial for short-range robot steering. 

Due to close proximity of robot camera to ground very useful 

details about salient features of the terrain can be detected at 

Figure 2. (a) A Rough Terrain, (2) Obstacles Geo-Location 

Map 

 (c) Generated Free Path, (d) Close-up View of Generated Free 

Path
this stage and characterized with higher degree of confidence. 

As a robot traverses natural terrain, images may be 

periodically acquired for traversability assessment. In each 

period, condition of the terrain can be classified based on the 

relevant features extracted from the images. One good 

method of embedding human knowledge is to apply fuzzy 

logic classification system. Human knowledge can be 

integrated in terms of knowledge base (i.e., fuzzy rule sets and 

membership functions). One method also for terrain 

condition assessment is to perform object surface texture 

analysis. Objects in different natural terrain have certain 

distinctive texture properties. The common surface texture 

attributes include: contrast, variance, energy, entropy, and 

homogeneity. Image texture is basically due to arrangement 

of pixel intensities variations that form certain repeated 

pattern(s). Image repeated patterns are caused by physical 

surface properties of terrain objects, such as rocks roughness, 

sand piles waviness, and so on. They could be result of light 

reflectance from surface of an object. One reliable way to 

classify textures is to apply quantitative statistics. 

An image is a matrix of pixel intensities, Ii,j. We can define 

co-occurrence of image matrix as Pi,j such as every entry in 

co-occurrence matrix, Pdi,j, is difference in intensity between 

a pair of image pixels(i and j), that are distance d pixels apart 

in original image in a given direction. With this notation, the

Energy associated with an image that is a measure of textural 

uniformity of an image is defined as: 

Image Energy reaches its highest value when its image pixel 

intensity level distribution has either a constant or a periodic 

form. Furthermore, Image Entropy is a measure of disorder 

of an image and achieves its largest strength when all elements 

in the P are equal. Entropy is inversely proportional to 

Energy and is defined as: 

Image contrast, on the other hand, is a difference of the P and 

it measures the amount of local variation of an image. The 

image contrast is measured by: 

Image homogeneity is inverse different moment measures of 

image and achieves its largest value when image pixel 

intensity repetitions are concentrated near the main occurrence 

matrix diagonal. The image homogeneity is defined as: 

In order to minimize the computation requirement, we choose 

the contrast, variance, and energy texture attributes as basis 

for terrain surface texture analysis. They provide reliable 

statistical assessment of a terrain object surface texture, in 

particular, when small image window are analyzed to assess 

the terrain condition. 

In our approach, we divide a full size terrain image into 

hundreds of finite (small) sub-windows. For each finite image 

sub-window, we perform surface texture analysis and apply 

fuzzy logic rules for classification of the terrain. This process 

is analogous to stress state analysis of a loaded mechanical 

part when subjected to Finite Element Analysis (FEA). In a 

FEA process, stress state of each finite element is individually 

computed under physical constraints and restriction and then 

stress states of computed finite elements are aggregated to 

assess the complete stress state of the object under applied 

loads. We follow a similar approach. We initially conduct 

terrain traversability assessment on individual finite subwindows of image independent of context of the whole image, 

and then aggregate the results to achieve terrain traversability 

assessment measures and classifying salient features of the 

nature terrain vigorously. 

This method has two benefits. First, it allows much simpler, 

yet more inclusive fuzzy rule system to be developed for 

terrain traversability assessment purposes. Secondly, the 

method offers an opportunity for performing parallel image 

processing since each sub-window image can be 

independently analyzed. This feature can expedite terrain 

traversability assessment considerably if the robot has onboard 

parallel computation capability. For development of fuzzy 

rules and membership functions, we chose a set of natural 

terrain image samples randomly selected from among many 

salient features of different terrains. We asked some terrain 

experts to classify terrain conditions at locations where the 

finite image sub-windows were taken. In parallel, for each 

finite image sub-window we computed their corresponding 

image surface texture properties. We compiled over 200 

different natural terrain data patterns. By considering range of 

texture attributes variation of these sample data, we developed 

a set of suitable fuzzy logic membership functions and fuzzy 

rule systems that closely mimic the human expert's judgment 

of the terrain traversability. 

 

4. TERRAIN TRAVERSABILIY 

ASSESSMENT ALGORITHM 

Table 1 summarizes the algorithm we discussed above. The 

algorithm performs identification, localization, and 

recognition of rock formations and generates a collision free 

traverse path based on the optimization technique discussed 

earlier in section 3. The algorithm initially enhances the 

image by removing noises and applies a Canny edge detector 

to extract out rocks edges. Next, an adaptive binarization 

convolution method is applied to binarize the image. The 

result is the blobs of rock formations with enhanced edges. 

( , ) (1) 2 Energy P i j

i j

∑∑ d =

= −∑∑ −

i j

d Entropy (i j) log P (i, j) (2) 2

( ) ( , ) (3)

2

Contrast i j P i j d

i j

=∑ ∑ −

, ( ) (4) ( , )

2 i j

i j

P i j Homogeneity

i j

d ≠

−

=∑∑
The algorithm sorts the rock blobs according to their size and 

ignore the smaller rocks that can be negotiated with the robot 

during mobility planning phase. The remaining rock blobs are 

treated as obstacles that the robot needs to avoid. The 

algorithm computes center location and principle moments of 

the rock blobs. 

The algorithm uses a Fuzzy Logic Terrain Classifier (FLTC) 

to compute a certainty confidence factor for each detected 

rock blob. The objective of FLTC is to verify that indeed the 

detected blob has surface texture similarity close to that of a 

rock. Using texture analysis method, we compute image 

intensity contrast, energy, and variance, as well as rock blob 

area. The first three attributes yield the most consistent 

indication of the rock texture formation. The last attribute 

helps with the physical size classification of the rock. The 

image texture attributes are used as input to the FLTC. Figure 

3 presents nine cases by which we geometrically characterize 

the shape formation of the rocks. Figure 4 presents the fuzzy 

membership functions corresponding to these image texture 

attributes. The fuzzy inference engine of FLTC classifies the 

rocks based on a certainty confident level. Figure 5 illustrates 

the fuzzy output membership functions considered for this 

purpose for classification of rock formations. After 

verification of the rocks, we apply a geometrical analysis 

scheme to characterize geometrical formation of each detected 

rock. 

Table 1. Algorithm for Terrain Traversability Path Planning 

and Assessment

1. Apply a low-pass filter to reduce noise. 

2. Apply an Adaptive Binarization to binarize the image. 

3. Apply a blob detector to isolate rocks bigger than a size 

threshold level. 

4. Compute texture attributes of next largest rock blob. 

5. Apply fuzzy logic rock classifier to determine rock 

detection certainty. 

6. If rock detection certainty is above a threshold value, 

compute center location and principle moments of the 

rock blob; otherwise continue with step 4. 

7. Characterize and model the rock geometry and log in its 

coordinates, orientation, and geometrical configuration 

and dimension; if more rocks are remaining for analysis, 

continue with step 4. 

8. Map location of each rock to the world 

9. Apply the divide-and-conquer collision free traverse 

pathfinder as described in section 3 to generate nearoptimum traversable trajectory paths for the robot. 

10. Select a feasible trajectory path with the highest measure 

of traversability.

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Figure 3. Nine rock formation models and their dimensional 

measurement probing methods.

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measurement probing methods.

Figure 4. Input Membership Functions of Fuzzy Logic 

 Rock Classifier 

Contrast

Energy

Rock-Blob Area

Variance

Figure 5. Output Membership Function of Fuzzy Logic 

 Rock Classifier 

Roughness
Of a particular importance is boundary formation of each rock 

around its first moment axis and mass distribution of the rock 

around its first moment. Two factors that control the shape 

appearance of the rock. We model the shape of rocks in our 

virtual simulation environment using either hemi-spherical or 

ellipsoidal geometrical representations. We use hemispherical rock representation to model that class of rocks 

appeared to have square dimensional proportionally. For the 

rocks appeared to have rectangular configuration, however, 

we use one of the nine models depicted in Figure 3. We 

construct an ellipsoidal object using a lofting technique 

applied in CAD software for construction of solid objects. A 

loft is result of surface formation achieved by connecting 

contour of several parallel construction polygons together. To 

model each rock as a loft, we use the first principle moment 

axis of the rock and create eight spaced, parallel, semi-circles 

construction polygons with varying diameters proportional to 

circumferential diameter of the rock in normal direction to its 

first principle moment axis. Depending on the orientation of 

the rock's first principle moment axis, the algorithm selects an 

appropriate rock model representation. The circumferential 

diameter of the rock is measured in incremental distance along 

longitudinal direction of the rock's first principle moment axis. 

Line segments A0 through A8 shown for each rock model in 

Figure 3 illustrates position and direction of measurement of 

the rock's circumferential diameters. Measurement is 

accomplished by image probing along the line segments Ai 's

in the binary image. See Figure 6b. In the final step of this 

algorithm the path planning technique described in section 3 is 

applied to generate a near optimum free path for the robot. 

Figure 6 presents terrain modeling and geo-location 

distribution of rocky surface of a Martian Terrain. 

5. PERFORMANCE MEASUREMENT 

The proposed terrain traversability assessment method was 

tested for assessment of several natural terrains. We chose 

several B/W and Color images taken by Pioneer and 

Opportunity Mars rovers from Mars terrains. The images 

were in size 320x240 pixels. We chose square sub-window 

frames of size 20x20 pixels for terrain assessment sampling. 

Figure 7 and 8 shows the results analysis of four different 

types of Marian terrains. The six terrain classifications are 

performed for each terrain. The classes of sub-terrain 

conditions that were classified were: (S) sandy, (V) very 

small rock, (m) rough, (M) very rough, (B) big rocks, and (U) 

uncertain. The algorithm classifies those areas of terrain that 

are unknown to its internal fuzzy logic model as "uncertain". 

Another situation that algorithm classified terrain as uncertain 

is at the border near to horizon line. Due to loss in depth of 

view, objects appearing near to horizon line cannot be 

uniquely differentiated and classified properly. As shown in 

Figure 7b, the terrain assessment map shows uncertainty about 

the terrain context at two rows near to horizon line. 

Depending on pitch angle of the camera, the perception of 

terrain weakens in the image frame as we move from bottom 

of the image toward to top. This problem is more severe 

 during route planning phases where the camera is looking 

directly straight toward the horizon with pitch angle near to 

zero. However, this problem tends to be troublesome for 

navigational planning phases (since the camera is pitched 

more toward the ground and terrain content appears manifestly 

in the image frame). Notice this observation in Figure 7c. 

The Terrain Traversability Assessment Measure (TTAM) that 

we used to evaluate the performance of the fuzzy logic terrain 

classifier was: 

(a)

(b)

(c)

Figure 6. (a) An Image of Mars Terrain, (b) Localized Rock Blobs 

(c) Modeled Terrain
Where, Mij is either 1 when terrain is classified correctly, 

otherwise 0. wij is a weight factor that reflects value 

criticality of terrain classification. It may be assumed flat 

unity for all different classes of terrain condition, or assigned a 

range of values based on a degree of belief one may have on 

reliability of classification of the system. We chose the latter 

alternative. We selected the range of values of wij according 

to the following scheme: 

Sandy Terrain: 1.0 Very Rough Terrain: 1.3 

Very Small Rocks: 1.0 Rocky Terrain: 1.5 

Rough Terrain: 1.2

5. EXPERIMENTAL SYSTEM SETUP

To experimentally verifying the proposed rock detection 

techniques and navigational path planning technique, we 

constructed a terrain mock up similar to Planet Mars surface. 

Figure 9 presents the physical Mars mock up test bed. The 

test bed provides a sand pile in size of 16 x 12 feet and rocks 

of various size and shapes. Our laboratory has several allterrain robotic platforms. Our robots are equipped with laser 

scanner, sonar, and stereovision cameras. Many smaller 

rocks cannot be detected using either laser scanner nor the 

sonar sensor suit located around the robot since the elevation 

of the sensors is too high related to the height of the smaller 

rocks we have. This necessitated usage of camera to visually 

inspect the rough terrain during navigation. 

As a part of this original investigation, we did not employ 

stereovision capability of our robot, though it is possible to 

fuse visual and stereovision results to achieve more robust 

analysis of the terrain [4]. Moving on soft sand pile creates 

not a major problem for our all-terrain robots. Our robots are 

relatively heavy and compacts the soil under theirs wheels that 

results good traction for the robot. They also benefit from allterrain tire rims that provide a sturdy traction with the ground. 

However, traction losses become on steep slopes. Due to the 

later problem, dead-reckoning cannot be respected and visual 

localization relative to landmarks is a better method for 

localizing the robot. We are currently implementing the 

algorithms on our robot supervisory controller called CORMI. 

CORMI stands for Cooperative Robotic Man-Machine 

Interface that is developed using FMCell robotic modeling and 

control software. FMCell provides an intuitive man-machine 

interface tools for control, sensor and image processing of 

cooperative robotic systems. Our reference [11] provides a 

detail description of our Cooperative Robotic Man-Machine 

Interface (CORMI). 

 

6. 

(5)

.

x 100% ∑ ∑

∑ ∑ =

i

ij

j

i

ij ij

j

w

w M

TTAM

(b) (a)

(d) (c)

Figure 7. (a) A Mars Terrain, (b) Fuzzy Logic Terrain 

Assessment Results. The Designation Are: (S) Sandy, (V) Very 

Small Rocks, (m) Rough Terrain, (M) Very Rough Terrain, (B) 

Big Rock, (U) Uncertain, (c) Another Mars Terrain, (d) Fuzzy 

Logic Terrain Assessment Results. Figure (b) and (d) are 

colored coded. 

(b) (a)

(d) (c)

Figure 8. (a) A Mars Terrain, (b) Fuzzy Logic Terrain 

Assessment Results. The Designation Are: (S) Sandy, (V) Very 

Small Rocks, (m) Rough Terrain, (M) Very Rough Terrain, (B) 

Big Rock, (U) Uncertain, (c) Another Mars Terrain, (d) Fuzzy 

Logic Terrain Assessment Results. Figures (b) and (d) are 

colored coded. 
CONCLUSION 

In this paper, we have discussed some of the navigational 

challenges associated with path planning of mobile robots in 

natural terrain navigation traversability assessment and 

presented a method for route planning and navigation planning 

in rough terrain. The proposed method applies imagery 

techniques for detection and localization of terrain salient 

features. For route planning, we have proposed a divide-andconquer near-optimum path planner method that is both fast 

and robust in generating collision free trajectory path plans. 

We have also presented a method for terrain traversability 

assessment and characterization based on a fuzzy logic 

approach. Both approaches are fast and can be readily 

implement onboard mobile robot to assist the robot with 

terrain path planning and traversability assessment online. 

7. ACKNOWLEDGEMENT 

This research was conducted under NASA Faculty Award for 

Research grant under contract number 1248358. The support 

from NASA is acknowledged. Furthermore, we acknowledge 

Dr. Edward Tunstel, Senior member of Engineering staff at 

JPL for technical monitoring of this research project and 

providing invaluable recommendations for enhancement of 

this research effort. 

Figure 9. Mars Mockup Arrange at Intelligent Tactical 

Mobility Research Laboratory at TSU. 

REFERENCES

[1] Howard A., Tunstel E., Edwards D., and Carlson A., 

"Enhancing Fuzzy Navigation Systems for Mimicking 

Human Visual Perception of Natural Terrain 

Traversability," in the Joint 9th IFSA World Congress 

and 20th NAFIPS Int. Conf., pp. 7-12, Vancouver, B.C., 

Canada, July 2001. 

[2] Kubota T., Nakatani T., and Yoshimitsu T., "Path 

Planning for Planetary Rover Based on Traversability 

Probability," In 7th Int. Conf. on Advanced Robotics, 

Sant Feliu (Spain), Sept. 1995. 

[3] Cherif M., and Laugier C., "Dealing With Vehicle/Terrain 

Interaction When Planning the Motions of a Rover," in 

the IEEE International Conference on Intelligent Robots 

and Systems, Munich (Germany), Sept. 1994. 

[4] Olson, C. F., Matthies, L. H., Wright J. R., and Li R., and 

Di K., "Visual Terrain Mapping for Mars Exploration," 

IEEE AC paper #1176, 2003. 

[5] Golda D., Iagnemma K., and Dubowsky S., "Probabilistic 

Modeling and Analysis of High-Speed Rough-Terrain 

Mobile Robots," in the Proc. of the 2004 IEEE Int. Conf. 

on Robotic and Automation, New Orleans, LA, April 

2004. 

[6] Iagnemma, K., Golda D., Spenko, M., and Dubowsky S., 

"Experimental Study of High-speed Rough-terrain Mobile 

Robot Models for Reactive Behaviors," Proc. of the Int. 

Symp., on Experimental Robotics, Italy, 2002. 

[7] Sirisha R., and Shirkhodaie A., "Visual-Servoing and 

Navigation of Mobile Robots for Targeting Applications 

With Laser Sensory Data Fusion," IEEE SSST 33rd 

Southeastern Symposium on System Theory, March 18-

20 2001. 

[8] Shirkhodaie A., "Second Annual Research Progress 

Report," submitted to JPL, Tennessee State University, 

Department of Mechanical and Manufacturing 

Engineering, July 2004. 

 [9] Shirkhodaie, A., "Visual Telerobotic Task Planning of 

Cooperative Mobile Robots," 1st NASA/JPL Project 

Progress Technical Report, July 2003, Tennessee State 

University, Department of Mechanical and Manufacturing 

Engineering. 

[10] Shirkhodaie, A., "Visual Telerobotic Task Planning of 

Cooperative Mobile Robots," 1st NASA/JPL Project 

Progress Technical Report, July 2003, Tennessee State 

University, Department of Mechanical and Manufacturing 

Engineering. 

[11] Devgan, T. P., "Man-Machine Interface for Teleoperation 

And World Perception Modeling of Cooperative Mobile 

Robots," M.S. Thesis, Department of Mechanical and 

Manufacturing Engineering, Tennessee State University, 

August 2003. 

Introduction to Issues in Developing Adaptive Intelligence

Gary Berg-Cross 

What are the issues to developing and measuring the intelligence of adaptive systems, how are they defined and 

what is the background to the issues? Given these questions it seemed to make a sense to present a top-down 

introduction to this in order to facilitate discussion such as we might have in a panel. 

A major context for a track on developing adaptive intelligence includes the foundational assumptions laid out 

by Albus (1999) in “The Engineering of Mind” which lays out a reference model architecture that serves as a 

principle vein of work on the design of intelligent systems. Jim Albus (1999) is based on functional, control 

and goal-oriented pragmatic principles using 2 assumptions. His first assumption is that the function of the 

mind/brain is to generate and control intelligent behavior. A second assumption is that intelligent behavior is 

understood as “appropriate action” in an uncertain environment where appropriate action is understood as action 

which increases the probability of success in achieving high priority goals. While Albus’ approach includes 

pragmatic concepts it grows out of control theory and what Haugeland calls GOFAI, Good Old Fashion AI” . 

To this meta model Albus adds a specific architecture for intelligent behavior as the result of goals and plans 

interacting at many hierarchical levels with knowledge represented in a multi-resolutional world model 

(discussed at greater length in Albus and Meystel, 2002). A general theoretical reference model for mind is 

axiomatically defined by Albus using 5 key concepts and their assumptions enables the approach. Briefly, these 

are function components, structural storage, interconnected computational modules in a control system 

architecture, hierarchical layering of components and attentional selection. These are depicted in Figure 1 and 

detailed as follows: 

1. The functional elements of an intelligent system are: behavior generation, sensory perception (filter, detect, 

recognize, interpret), world modeling (to store knowledge, predict and simulate future), and value judgment (to 

compute cost, benefit, and uncertainty attributes). These elements are detailed by sub-activities. As an example 

behavior generation is based on planning and control of actions designed to achieve behavioral goals. The 

planning a process itself is complex and: 

1. assigns responsibility to agents/ computational elements for jobs, and allocates resources to agents to 

perform assigned jobs, 

2. hypothesizes strings of actions (plans) for agents from a “vocabulary” of possible actions to 

accomplish jobs, 

3. simulates and predicts the results of executing these hypothesized plans, 

4. evaluates the predicted results of the hypothesized plans, 

5. selects the hypothesized plan with the most favorable results for execution. 

In general Albus’ functional elements, while computational in principle, evoke many appealing cognitive 

concepts such as meaningful transformations, risk, benefit, importance, advantageous goals etc. Biological 

correlates to functions are noted (but since this is a moving target, may need to be revised over time). 

2. These functional elements of an intelligent system are supported by a knowledge database that stores (both 

long-term and short-term) a priori and dynamic information about the world in the form of state variables to 

record state-of-the-world, symbolic entities (as in GOFAI), symbolic events, rules and equations, structural and 

dynamic models, task knowledge, signals, images, and maps. It is worth noting in passing that Joslyn (2000) 

understands Albus’s overall approach to be one of semiotic control system using models, such as stored in a 
knowledge base providing the special property of intelligence and combined with control systems to purposely 

organize functions such as listed above. 

3. In the reference architecture the functional elements and knowledge database described above can be 

implemented by a set of computational modules that are interconnected to make up nodes in a control system 

architecture. Exemplars of such nodes are found in the Real-time Control System (RCS) built at NIST. Each 

node is part of a control system that performs the 4 basic processes -sensing, maintains a world model, 

computing values, and generating behavior and their supporting sub-processes (planning, task decomposition 

etc.). To Albus a node corresponds to a functional set of brain neurons closing the loop between afferent and 

efferent neural pathways. Interestingly conceptually this architecture does not directly address components that 

do not lop between afferent and efferent parts and thus makes them a secondary sub-component. 

4. The complexity inherent in intelligent systems can be managed through hierarchical layering, which is a 

common method for organizing complex systems that has been used in many different types of organizations 

throughout history for effectiveness and efficiency of command and control. A key to hierarchical control is that 

higher level nodes have broader scope and longer time horizons, with less concern for detail, while lower level 

nodes have narrower scope and shorter time horizons, with more focus on detail. Elements may be deliberative 

or reflexive throughout the hierarchy 

5. The complexity of the real world environment can be managed through a strategic process of focusing 

attention. Since the world is not uniformly important this serves the needs of an agent with limited 

computational resources. 

Attention focuses sensors on task-relevant objects. 

Taken as a whole Albus believes that work based on this reference model helps advance the scientific inquiry 

into of the nature of mind, and also will very likely also lead to practical improvements in intelligent machine 

systems technology for many fields. A number of practical achievements can be pointed to, but it may be 

useful to relook at the overall architecture, its assumptions and details. 

Figure 1 RELATIONSHIPS BETWEEN ALBUS’ FUNCTIONAL ELEMENTS 

KNOWLEDGE 

DATABASE

SENSORY 

PROCESSING

BEHAVIOR 

GENERATION

PLAN

PREDICTED 

INPUT 

UPDATE

STATE

PLAN 

RESULTS

PLAN

SITUATION 

EVALUATION

OBSERVED 

INPUT 

COMMANDED 

ACTIONS (SUBGOALS) 

PERCEIVED 

OBJECTS & 

EVENTS

COMMANDED 

TASK (GOAL)

OPERATOR 

INTERFACE

VALUE 

JUDGMENT

WORLD 

MODELING

Perception Planning and Control

EVALUATION
A context for this discussion is a section from last year’s PerMIS conference (Machine Intelligence: Measures 

& Issues II ) which raised some issues relevant to the architecture and its assumptions. These included: 

a. Going beyond sequential, functional, hierarchical architectural ideas to include how intentions 

and adaptive abilities emerge to provide the roots of “intelligent” agent actions (Berg-Cross, 

2003). 

b. How to understand intelligence performance when we consider how natural agents (individual 

humans and animals) readily adapt to rapidly changing and/or complex environments including 

rare, ambiguous, and unexpected events. An example of how might artificial intelligence might 

adapt was presented by Gunderson (2003) considering a robotic intelligence that has a robust 

ability to “develop” hypotheses to solve problems and thus starts chasing the family dog to more 

effectively (intelligently) perform housekeeping. 

c. Moving towards “natural intelligence” might intelligent information-processing bridge between 

differently-scaled models by means of cross-scalar coherence and autonomy-negotiation to 

create a hyperscalar system (Cottam, 2003). 

d. How valuable are functions of creativity and playfulness in intelligent systems when considered 

as part of an adaptive learning and developmental process? Is there a common architecture that 

includes interaction, adaptation, innovation and “immunity” (Arata, 2003). 

e. Strong AI vs. Weak Ai asked the question on how important specific models found in knowledge 

bases versus general and abstract know. But much of the human knowledge seems inconsistent, 

loosely organized, and in perpetual flux rather than faithful copies of reality found in 

implementations of both strong or weak AI. The mind may neither be a highly organized 

knowledge base nor a large set of fuzzy images. A concept developed by John Sowa is 

knowledge soup. Knowledge is fluid, lumpy, with adherable chunks of Theories, Models and 

Hypotheses that float in and out of awareness. Is it useful to of considering agent knowledge as 

a fluid rather than precise system of “true” facts (Berg-Cross, 2003). 

Taken together these question some of the foundational assumptions laid out by Albus in “The Engineering of 

Mind” and suggests modifications if not major overhaul to reference model architecture. We agree that the 

scope to resolve these issues will be broad requiring understanding and cooperative work from: 

1. Neurosciences 

2. Cognitive Sciences and cognitive information processing 

3. Artificial Intelligence 

4. Learning and Complex Adaptive Systems 

5. Intelligent Control 

6. Robotics and Intelligent Machines 

7. Intelligent Manufacturing Systems 

8. Game Theory and Operations Research 

9. Image Understanding 

10. Planning and Reasoning 

11. Philosophy 

12. Linguistics and Speech Understanding 

As an example, much of neuroscience models (for example perceptual cognition) are network rather than 

hierarchical models. While it is good for engineering to ruese the same functional the basic “unit” of neural 

computation does not seem to share the same processing components as we move from one level to another. 
Berg-Cross (2003) notes separate, but fundamentally different functioning to support the high-level beliefintention parts of intelligent behavior and, at least in human architectures, these seem significantly different 

from the lover level functions. This is related to the argument of how easy or practical it currently is to engineer 

intelligent systems (hierarchy simplifies the engineering) as opposed to letting them develop. 

Another issue concerns the “meaning” and measurement of autonomy of a system that is learning, modifying its 

knowledge and adapting its behavior. Understanding the interaction of these components over time is a central 

part of understanding how an agent arrives at “appropriate action” to increase the probability of success in 

achieving high priority goals. How important is self-organization and development? 

Finally it is worth noting that some “general principles” for complex systems may be useful to discuss for 

intelligence. The phenomena of pattern formation and self-organization found in nonequilibrium physical, 

chemical and biological systems may be governed by a number of general principles. This idea, arising in the 

natural sciences study of complex systems structureal development, has now been applied to discussion of the 

development of intelligence. It is a new way to bridge the gap between what individual element function, such 

as RCS nodes, and what many of them do when they adapt/learn/evolve to function “cooperatively” . 

An issue then is how GOFAI and engineering approaches might be supplemented by research strategies and 

computational tools growing out of nonlinear dynamical systems. Numerical and analytical investigations of 

these systems lead to new mathematical results and problems, as well as to formal bridges to other biological 

and physical systems, notably dissipative systems that describe aspects of self-organization and nonequilibrium 

behavior. These formal investigations have already suggested new designs for computer vision, adaptive pattern 

recognition machines, and autonomous robots, and as an integrative approach may provided basic science with 

designs of adaptive intelligent systems. As an example, in the study of complex systems, especially natural ones, 

the idea of emergence is used to explain development of patterns, structures, and/or properties that do not seem 

reducable to a system's existing components and their linear interaction. Emergence becomes of increasing 

important as explanatory constructs for complex systems characterized when: 

• Global, system organization appears to be of a different kind than functional components alone; 

• Components can be changed or even removed without an accompanying loss of function of the higher 

functions of a system. 

In concluding, adaptation and learning are seen as one of the central points of such IS research, but diverse 

approaches may be meaningfully integrated into thinking about the future of Intelligence Systems. We advocate 

an integrative approach - let us not be stymied about differences and together keep doing interesting things. In 

this panel, and in the track as a whole we hope to discuss core ideas and explore approaches that will possibly 

shape future work in the area of adaptive intelligence. 

References

Albus, James.S. (1991). “Outline for a Theory of Intelligence”. IEEE Transactions on Systems, Man and Cybernetics, 2 1 

( 3): p. 473-509 
Albus, James S: (1999) "The Engineering of Mind", Information Sciences,v.117, pp. 1-18 

Arata, L., Interactive Measures and Innovation, presented at PerMIS 2003. 

Berg-Cross, G., A Pragmatic Approach to Discussing Intelligence in Systems, presented at PerMIS 2003. 

Cottam, R., Ranson, W., Vounckx, R., Abstract or Die: Life, Artificial Life and (v)Organisms, presented at 

PerMIS 2003. 

Gunderson, J., Gunderson, L., Mom! The Vacuum Cleaner is Chasing the Dog Again!, presented at PerMIS 

2003. 

Joslyn, Cliff: (2000) "Towards Measures of Intelligence Based on Semiotic Control'', 2000 Workshop on 

Performance Metrics in Intelligent Systems, ed. A. Meystel, NIST 

Meystel, Alexander M and Albus , James, Intelligent Systems: Architecture, Design, and Control

2001 
1 

PERMIS 2004 

Developing Rational-Empirical Views of 

Intelligent Adaptive Behavior 

Gary Berg-Cross, Knowledge Strategies 

Potomac, Maryland 20854, USA 

Abstract 

A developmental perspective is useful to understand how 

intelligent human behavior comes to be performed because it 

combines insight of evolutionary factors that enable dynamic 

genetic-environmental interactions within individual humans. 

Such developmental adaptations may now be studied 

experimentally using developmental and epigenetic robots. 

Resulting insights is a useful step toward more complete, valid 

understanding of intelligent behavior, its adaptive nature and it 

structural roots. Taken together these broaden the concept of 

“engineering mind” to include the larger concept of 

“development”. This paper overviews recent work of 

evolutionary and developmental psychology, epigenetic robots 

and cognitive science. A synthesis of these suggest means by 

which the fluid nature of adaptive knowledge arises 

developmentally within a heterogeneous architecture adapted 

for adaptation itself as part of a rational-empirical process. At 

this top-level of intelligence, situation-specific adaptive 

functions are processed using a dynamic mix of belief-based, 

rational-empirical cognitive processes and socialized methods 

adjusted within human cultures. General research goals of 

such an integrated, consilient view of intelligence are outlined 

for future research. 

1. Introduction 

In “The Engineering of Mind” (Albus, 1999) cited a range of 

research which, taken together, provided new insights into the 

nature of mind. These included work on learning & language, 

image understanding, rule based reasoning & planning, 

advances in real-time sensory processing using world 

modeling and data fusion, intelligent hierarchical controls, and 

effective use of parallel processing on focused attention as 

well as general progress in the cognitive/ neurosciences. Albus 

(1999) argued that what was lacking was synthesis of a 

“general theoretical model which ties all these separate areas 

into a unified framework that includes both biological and 

machine embodiments of the components of mind”. Building 

on earlier work (Albus 1991) structured a reference model 

using widely discussed concepts of intelligence and mind – 

controlled behavior generation, via underlying knowledge 

bases and world models choosing goal appropriate action in 

uncertain environments. Berg-Cross (2002, 2003) noted that 

much of this underlying reference model represents a midlevel, plan based on a symbolic information processing view 

of intelligence which is amenable to hierarchical modeling and 

engineering, but which may not capture the full complexity of 

intelligence. For one thing, Albus reference architecture of 

mind is organized around a small number of general purpose 

mechanisms that are assumed to be content-independent. The 

functional modules have a variety of names such as "learning," 

"induction," "cognition," "world modeling," "or “sensor 

fusion”. In Albus’s information processing views these are 

organized around the world model, which combines with the 

other functional mechanisms to explain how an agent acquires 

a language or learns to navigate city driving. 

Another way to view such phenomena is as a result of a 

rational process. Anderson (1990), for example, processes 

identifies 6 steps developing a theory of rational agents: 

(1) Goals: specify precisely the goals of the cognitive 

system. 

(2) Environment: develop a formal model of the 

environment to which the system is adapted. 

(3) Computational limitations: make minimal assumptions 

about computational limitations. 

(4) Optimization: derive the optimal behavior function, 

given 1–3 above. 

(5) Data: examine the empirical evidence to see whether 

the predictions of the behavior function are confirmed. 

(6) Iteration: repeat, iteratively refining the theory. 

This paper addresses some aspects of an analysis of steps 1 

and 2 recognizing the evolutionary roots of some goals and the 

essential importance of adaptation within the environment. 

2. Unifying Views 

As previously noted Berg-Cross’s (2002) proposed a 

fundamentally different reference architecture than Albus 

(1999). A portion of this 3 part architecture is shown in the 

left portion of Figure 1. While not strictly hierarchical it is 

easier to introduce it in top, middle and bottom terms. There is 

an upper level for belief-intention driven pragmatic processes 

which provides intentional control and strategic guidance. In 

a lower level there are situated-reactive processes which also 

pass factual input to intermediate planning level. This 

architecture is beyond the traditional scope of engineering 

which attempts to decompose functions using mechanistic 

principles, but does reflect some pragmatic elements of the 

view of mind found embedded in Albus 1

(1991). In particular 

the reference model provided a pragmatic view, shown in the 

middle portion of Figure 1, to the ubiquitous cognitive idea of 

a "rational agent' using 'knowledge' to 'succeed' in the world. 

Berg-Cross (2003) identified two key aspects that structure the 

new reference architecture: 

 

1

 “Intelligence is a faculty of the system that provides an 

ability of a system to act appropriately in an uncertain 

environment, where appropriate action is that which increases 

the probability of success, and success is the achievement of 

behavioral sub-goals that support the system's ultimate goal.”
2 

• Unification of a belief-based, rational-empirical view 

of intelligence, reasoning & knowledge 

o for example, propositional representations are 

not primary knowledge but an ingredient to 

which becomes knowledge via interpretation. 

Thus there is a relation between propositions and 

the system of beliefs that cognitive agents 

know/use 

• Characterization of agent knowledge as a fluid, 

inconsistent mix of approximate facts, hypotheses, 

goals and concepts that serve in a rational-empirical 

process (Sowa, 1999). 

 The current paper addresses a developmental perspective to 

further explain how pragmatic foundation for these constructs 

come into existence. It finds features of rational-adaptive 

nature of intelligence embedded in biological systems. This 

shown in the right side of Figure 1 which provides a very 

high-level view of the evolutionary and developmental 

influences to Sowa’s (1999) rational-empirical knowledge 

cycle. In particular these help address the questions of 

primitives of cognitive processes within a rational-empirical 

cycle and how they might arise developmentally. These are 

not new questions, but discussion in the context of aspects of 

the reference architecture is. Both an evolutionary and 

epigenetic approach is introduced to provide a richer, plausible 

basis for fluid, adaptive knowledge structures and processes. 

Overlaying this are additional social processes which further 

shape adaptive structures and knowledge. 

Discussion of the developmental nature of intelligence is in 

the spirit of unifying scientific approaches (Wilson, 1998) for 

biological, psychological and social science. A synthesis of 

these can enhance a strictly engineering view of mind. One 

initial goal is to add a biological frame to the information 

processing model and outline our understanding of intentions 

and beliefs that co-exist with rational and underlying reactive 

processes. A key idea uniting these is the adaptive nature of 

human intelligence and resulting human behavior which may 

be usefully viewed and discussed from 3 different points of 

view as a: 

1. species evolutionary product (see Caporael, 2001 for 

an overview of Evolutionary Psychology - a distal 

explanation operating over evolutionary time), 

2. result of broad epigenetic-environmental interactions 

within the lifespan development of individual 

humans/agents (such as discussed in Piaget 1950) and 

3. bio-ecological phenomena based on situationspecific functions processed by a rational-empirical 

cognitive apparatus that is socialized and adjusted 

within human cultures (Bronfenbrenner & 

Morris,1998). 

Each provides a useful, somewhat complementary, step to a 

more complete and valid understanding of intelligent 

behavior, its adaptive nature2

 and it structural roots. Taken 

together these broaden the concept of “engineering mind” 

Figure 1: Three Level Hybrid architecture, Sowa’s RationalEmpirical Knowledge Cycle, Evolutionary process articulated 

by Piagetian developmental processes 

 (Albus, 1991, 1999) to include the larger concepts of 

evolution, “development” and social influences on this 

development and to help understand the complexity of the 

issues. 

3. Evolutionary Views and Levels of Explanation 

The evolutionary perspective provides a biological view of our 

complex, characteristic intelligence in the form of a, neural 

system adaptive by evolutionary challenges. Thus, in an 

evolutionary perspective, such as posited by Evolutionary 

Psychology (EP), the human mind resides in a brain that is “a 

system of organs of computation designed by natural selection 

to solve the kinds of problems our ancestors faced in their 

foraging way of life” (Pinker 2000). Biology and thinking 

follow the same evolutionary path since long-term evolution 

has shaped all human minds as it has human bodies, around 

fitness structures and functions suited for hunter-gatherers. 

Current evolutionary neuroscience perspective on brain 

reorganization (left-right cerebral hemispheric asymmetries, 

human-like third inferior frontal convolution etc.) in light of 

brain imaging studies suggests the story that Homo 

intelligence arouse from a dynamically configured set of brain 

areas that collaborate adaptively to meet particular cognitive 

challenges. Evolutionary biologists (EB) do a form of reverse 

 

2

 Following Pfeifer & Scheier (1998) adaptivity may be 

understood as an organisms’ capability to modify its behavior 

so that they can more efficiently maintain their critical 

parameters in a “zone of viability”. The pathway to this 

includes all of species, group and individual development. 

Piaget includes such ideas within his equilibration process. 

Berg-Cross (2003)

Evolutionary Inheritance 

Substrate for processes, 

 predisposition for 

 causal concepts... 

Sensory Motor 

Schemata 

Abstract 

Schemata

Anticipation 

Development

Belief, Desire, 

 Intention 

(BDI) 

Guides 

Goal/PlanOriented 

Operational 

Cognition And 

Problem 

“Automatic” 

Reactive Base 

BergCross
3 

engineering3

 when they hypothesize adaptive problems a 

species might have encountered during its evolutionary 

history, and then ask themselves, "What would a machine 

capable of solving these problems well under ancestral 

conditions look like?" Using this insight, EBs empirically 

explore the design features of the evolved “machines” that, 

taken together, comprise an organism. This is a one form of 

evolutionary explanation, but its goal is a more integrated 

explanation at several levels. A view of the explanatory role 

of evolutionary principles in the context of other ideas (e.g. 

brain structure) is represented in Figure 2 based on a 

framework found in the work of Cosmides and Tooby (1987). 

Their work uses an evolutionary focus to propose an outline 

the human mind's “design”. Knowing what cognitive 

programs are posited to come into existence evolutionarily, in 

turn, guides the search for neural explanations as shown in the 

Figure. Taken together this theoretical outline of adaptive 

problems helps guide the integrated search for the cognitive 

programs that solve adaptive problems as part of integration 

of explanation. Wilson (1999) calls such integration across 

scientific disciplines consilience, a common ground of 

explanation that links scientific systems of thought. Belief in 

the possibility of consilience is a meta-assumption because 

systems of explanation do not spontaneously unify. 

Integration requires that a common body of abstract principles 

and related evidence be constricted and EP/EB suggests one 

such path for evolved intelligent agents. 

Figure 2: Three “complementary” levels of explanation in 

evolutionary psychology. Explanation at one level (e.g., 

adaptive function) does not preclude or invalidate explanations 

at another (e.g., neural, cognitive, social, cultural, economic). 

Constrained, plausible inferences between level s are 

represented by the arrows –after Cosmides and Tooby (1987). 

Such definitions of adaptive problems may not uniquely 

specify the design of the mechanisms that solve them, because 

as a rule, there are multiple ways of achieving any solution. 

As result empirical, psychological studies are needed to focus 

in on which mechanism nature may have actually adopted. 

The engineering principle here is that the more precisely 

researchers define an adaptive information-processing 

problem -- the "goal" of processing -- the more clearly one can 

see what a mechanism capable of producing that solution 

 

3

 Regular engineers figure out what problems they want to 

solve, and then design machines that are capable of solving 

these problems in an efficient manner. 

would have to look like. This research strategy has been used 

in the study of vision, for example, so that it is now 

commonplace to think of the visual system as a collection of 

functionally integrated computational devices, each 

specialized for solving a different problem in scene analysis -- 

judging depth, detecting motion, analyzing shape from 

shading, and so on. This differs from the type of engineered 

“mind” described by IP models which are essentially 

unspecialized with general-purpose mechanisms that subjects 

all information to the same processes and stores it in the same 

places. Faces, words, geometric shapes, most other sensory 

information will be perceived, processed, rehearsed, and 

stored in the same fashion. An evolutionary perspective brings 

the unsettling notion that the evolution of cognition has 

produced memory/knowledge systems that specialize in the 

processing of particular types of information. It is well known 

that human perceptions and reasoning are biased - involving 

anchoring and stereotyping, and parceling out reality 

according to the limitations of experience and that they tend to 

focus on what is considered important by the person (see 

Dawes 1988 for a summary). This perspective provides one 

useful idea of the varied and inconsistent basis of an 

individual’s knowledge – it is based on a mix of specialized 

modules. Seen at a distance the result is an intelligence that 

includes fluid, heterogeneous, ever changing, and often inconsistent knowledge leading to its characterization by Sowa 

(2000) as a knowledge soup. The soup metaphor serves to 

capture the idea of fluid material with solid chunks; corresponding to the pieces of alike kind of knowledge that have a 

type of internal consistency. Between chunks there may be 

inconsistency arising from various sources. This seems to be 

the case for the human visual system, for example. It is still 

early to say that a research program using this frame has 

yielded firm answers to many of the issues of intelligence. A 

number of issues revolve around the Tooby & Cosmides 

(1992) 6 meta-theory principles of adaptationism that may 

provide a coherent view4

: 

1. functional efficiency criteria for identifying 

adaptations shaped by natural selection, 

2. the context-sensitive psychological adaptation (rather 

than the “instinctive behavior”) as the appropriate 

level of analysis for human nature, 

3. a highly modular view of the mind comprised of 

hundreds of domain-specific psychological 

adaptations, 

4. a computational metaphor for the mind imported 

from cognitive psychology, 

5. the universality of evolved human nature rather than 

the heritability of individual differences, 

6. hominid small-group living in Pleistocene Africa as 

the most relevant ancestral environment for 

understanding most of human nature. 

 

4

 The last five of the six remain controversial, even among 

adaptationists 
4 

This meta-model remains controversial and it is not clear, for 

example, that point 3 is correct. It may be that adaptation has 

lead human mental abilities to use a "universal structure" or at 

least generalized/universal functions, which would simplify 

the measurement of intelligence. At this point we probably 

can say that the structure of computation-like neural networks 

has emerged in some form despite short-term influences which 

to Pinker includes culture, belief, or individual desires. But 

there is a large, interactive story to describe how these 

inherited structures serve an adaptive function to become 

phenotypic structures during development. I think it possible 

that an empirical-rational process is the general adaptive 

function. There is much to do to prove this hypthesis. 

4. Dynamic Development and the Epigenetic Robotic Approach

It seems useful to consider intelligent performance as part of a 

dynamic system in which agent architecture/engineering and 

its environment join forces over time creating agent 

“development”. A consilience-like convergence of data and 

theory from genetics, embryology, and developmental biology 

suggests to many the possibility of a more epigenetic, 

contingent, and dynamic view of how organisms develop 

(Lickliter & Honeycutt, 2003). 

Developmental dynamics, properly formulated, can add to 

proximal details to the distal view of evolutionary psychology. 

Putting it simply, development and evolution can usefully be 

considered 2 views of intertwined phenomena. The standard 

model is to view mechanisms of evolution as essential to 

understand development, and the mechanisms of development 

are likewise essential to understand evolution (Griffiths, & 

Gray, 1994, 2001). This was changed by such things as 

Waddington’s "Epigenetic Landscape" concept that “ the 

degree to which a trait is innate is the degree to which its 

developmental outcome is canalized which is defined as the 

degree to which the developmental process is bound to 

produce a particular end-state in the face environmental 

fluctuations both in the development's initial state and during 

the course of development.” Lickliter & Honeycutt (2003) 

hold the view that development is a self-organizing, 

probabilistic process in which order and pattern emerge to 

change as a result of transactions among developmentally 

relevant resources both internal and external to the organism. 

It follows that development should not be described as the 

result of the interaction between genetic and environmental 

factors, because neither operates as independent causes. In 

this dynamic view it is more accurate to say that development 

results from and bidirectional and dynamic transaction of 

genes, cells, tissues, organs, and organisms during the course 

of individual ontogeny. Lickliter & Honeycutt’s (2003) argue 

that a study of developmental dynamics could reveal how 

underlying mechanisms unfold over time and provide insights 

that are complementary to, not mutually exclusive with, the 

functional explanations already provided by evolutionary 

psychology. This has now begun to be studied using 

“epigenetic robots” designed using Piagetian ideas of 

development. When applying these ideas to the development 

of intelligence these formulations parallel some of Piaget’s 

(1950) views on adaptation to the environment. For example, 

Piaget introduced the term epigenesist to refer to such 

development, determined primarily by interaction rather than 

genes. Over the last few years biological thinking has emerged 

in a “new robotics” partly in response to lack of progress with 

the information processing paradigm which has proven illsuited to come to grips with natural, adaptive forms of 

intelligence (Pfeifer et al 2004). One sub-set of this, called 

epigenetic robotics, focuses on experimental studies of 

Piagetian stage-theory processes5

 involving prolonged 

epigenetic development6

. The approach is: 

1. Start with some ‘innate’ components/substrate (as 

previously discussed) 

2. Consider the nature and demands of the environment 

3. Let development proceeds by an interaction between 

developing components & a dynamic environment 

4. Along the developmental “path” temporary structures 

and processes may bridge to increasingly more 

complex cognitive structures (fitter ones) tuned to the 

environment by interactions with the environment 

(physical and social) 

This developmental path to intelligence provides a substantial 

set of intermediate knowledge products for an agent. By 

Piaget’s account, the sensori-motor stage in biological systems 

is a structuring process, where sensing mechanisms are 

gradually integrated with motor actuating mechanisms on the 

developmental path to a mature performing system. For 

human babies this takes lasts 2 years. The first four months 

organize a substrate of reflexive responses into more coherent 

motor strategies called physical schemas -scruffy knowledge 

structures proposed as the basis on which more abstract 

knowledge is built. In addition, sensory modalities are 

coordinated and attentional mechanisms begin to emerge – all 

satisficing environmental constraints and inherited motivators 

which are realized in a series of intermediate forms on the path 

to adult structures. From four to six months, reactions are 

“practiced” until an infant exhibits what seems like intentional 

 

5

 Piaget theory of children’s intelligence sees it is as controlled 

by construction of mental organizations, which he called 

schemes. These are used to represent the world and designate 

action. This adaptation is driven by a biological drive to obtain 

balance between schemes and the environment (equilibration). 

6

 One interesting aspect of this process is its underlying ability 

to deal with and solve complex multi-level integration 

problems – unsolved challenges in engineering intelligent 

systems. The epigenetic robotics paradigm proposes that 

epigenetic development allows systematic exploration of this 

complex issue. 
5 

prolonging of special interactions. Taken together this path 

evidences the emergence of a belief, desire, intention structure 

such as described in Berg-Cross (2002). In Piagetian terms 

stable agent-world interactions patterns emerge that are 

evidence of satisficing, temporary cognitive structure built in a 

bottom up fashion. These are initially constructed as physical 

schemata, but may be used by an agent to handle other 

instances of this type of interaction. In a fluid model of 

knowledge, knowledge starts as physical schemata , is 

extended to other physical examples of a phenomena. These 

extensions are often tentative and prove less than optimum for 

situations and are thus highly modifiable as discussed in the 

Sowa (2000) model of a rational-empirical “cycle”. 

Epigenetic robotic implementations can help clarify, evaluate, 

and even further such cognitive, developmental theories, 

which due to the complexity of the interactional processes 

involved have up to now remained somewhat speculative. An 

interesting line of psychological work suggests some direction 

for research into corresponding top-down processes, such as 

proposed in the 3 part reference architecture of Berg-Cross 

(2003). Gergely and Csibra’s (1998) have proposed a theory 

of the one-year olds ‘naïve theory of rational action’ based on 

evidence for causal and other beliefs such as are hypothesized 

as belief-desire-intention processes. Infants seem to 

“comprehend” a goal-oriented aspect of agent behaviour of 

agents (see Berg-Cross, 1971 for an early experiment into a 

child’s ability to detect intentions). This is also seen in the 

form and function of so called declarative pointing which is 

characterized by coordination of an extended arm and index 

finger intended to draw attention to a distal object. Unlike 

other pointing, it is not necessarily a request for an object. 

Instead, children often use declarative pointing to draw 

attention to objects when they are clearly outside their reach 

(e.g. the moon or a bird passing overhead). Further, 

declarative pointing only occurs under specific social 

conditions. Children do not point unless there is someone to 

observe their action. Other research on children’s attentional 

responses (using habituation) shows that they take goals into 

account and anticipate future actions in coordination with 

these goals. For example, evidence of “teleological” 

interpretation by a 1 year old can seen in their attributions to 

an agent desires (e.g. to drink water) as an explanation of an 

Figure 3 Teleological reasoning in infancy: the 

 infant’s naive theory of rational action (after Gergely. 

 and Csibra,1997) 

abstract figure’s jumping action over an obstacle. Controlled 

studies also show child beliefs (e.g. a belief that there is water 

in the bottle). Thus, there is developmental evidence for an 

early teleological model (see Figure 3) that over time can 

develop into an interpretive understanding of others as

intentional agents (i.e., agents that have mental states such as 

goals and desires, and whose actions are related to their goals 

and desires). This is a rational model that helps one agent 

predict the behaviour of another. The second point leads to 

the constructive, interpretive aspect of intelligence with 

evolutionary roots. These concern the origins and 

development of an understanding of others as

social/interactive agents that influence each other, interact 

with each other, and can have thoughts, emotions and 

dispositions about/towards each other. Developmentalists have 

long argued for its central role in child development. 

5. Social Roots of Rational Behavior 

A standard principle of rationality is that it operates under 

normal circumstances to optimize the adaptation of the 

behavior of the organism. A long research line, growing out 

of Brunswick (see Oaksford and Chater 1996), shows that 

people behave irrationally with respect to logic, but that the 

behavior is rational when the context is broadened to 

encompass a person’s ‘‘‘normal’’ life conditions’. One 

summary idea is that people can be seen to behave rationally 

with respect to the environment, where their behavior and 

underling intelligence has been structured and which evolution 

has provided a developmental substrate, but appear to be 

operating irrationally with respect to a artificial, experimental 

tasks. That is, adaptive behavior arises when intelligentcapable agents strive to maintain “ecological balance” of its 

relationship, both physical and mental, between their 

environment, material structure, and a degree of pragmatic 

control. 

Tying some of the previous discussion together, a plausible 

story is that certain biological features found in normal human 

infancy were selected by a social process, during the stages of 

human evolution post-dating the invention of tools. These 

features might have been selected for their facilitative value in 

the process of what Vygotsky's colleague Leontiev (1981) 

called 'appropriation'. Infancy is then seen as a specific niche 

in which adaptive parameters are set by processes of 

individual appropriation. In this account, the biology of human 

infancy is a product of the co-evolution of culture and biology. 

Recent studies of infant cognition and social behavior lend 

support to such an account. Infancy, in this account, played a 

crucial role in the 'socialization' of human biology. Thus at 

any given point an agent has a degree of adaptive intelligence 

but as a developing agent it has a measurable “zone of 

proximal task intelligence” (after Vygotsky , 1978). Within 

this zone agent have not yet master autonomous skill but has a 

belief and intentions to do with tasks the guidance of humans 

or more skilled agents. Social explanations of adaptation 
6 

problem are detailed by Bronfenbrenner and Morris (1998) 

who point out how the human individual is an active 

constituent of any context it inhabits. This way of theorizing 

emphasizes that social context, including child rearing, is 

inherently relational and that human life is part of an open 

system, characterized by indeterminacy and the creation of 

novelty. 

6. Summary

The views presented here provides an expanded view and 

framework of intelligence in the spirit of consilience. At a 

very high level, it represents a start on an integrated view of 

major aspects of human adaptation, including the development 

of approximate knowledge, the role of evolutionary substrate, 

intermediate structures and rational processes. A working 

hypothesis is that the proper use of epigenetic robotics may 

test developmental dynamic hypotheses and properly will over 

time add to the theoretical and empirical foundation of 

adaptive intelligence. Time will tell the merits of these 

concepts within a joint evolutionary and developmental. 

Relevant questions include those now attached to both 

evolutionary psychology and epigenetic robotic research: 

• Does the theoretical perspective guide researchers to 

new and important domains of discovery? 

• Does it lead to specific predictions about new, poorly 

predicted phenomena? 

• Does it explain existing scientific findings in a 

parsimonious manner (better than current theories)? 

• Does it yield significant new empirical data? 

• Does it provide new insights in the frequently argued 

issues with adaptation7

? 

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7

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exploration via robotics includes: 

• How much is inherited, the nature of motor 

primitives 

• Models of planning and control, perceptual-motor 

mapping, equivalence of actions. 

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Robotics: Design Principles for Intelligent Systems, 

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Knowledge (Alfred Knopf, 1998) 
Interactive Immunity and Adaptive Innovation 

Luis O. Arata 

Department of Fine Arts, Languages & Philosophy 

Quinnipiac University, Hamden, CT 06518 

E-mail: luis.arata@quinnipiac.edu

ABSTRACT

Autonomous systems must have the ability to operate on their own 

in dynamic, uncertain environments without breaking down. This 

paper presents concepts for the design and evaluation of selfrepairing systems that draw on current work on immune 

mechanisms and artificial immune systems. 

To survive in a dynamic environment we say that a 

constructed system must be able to adapt. The problem is how to 

implement the adaptive drive. This paper looks into one possible 

route: to model and implement features inspired by the immune 

system as a problem solving mechanism. This route does not 

exclude other adaptive mechanisms and can complement them. 

The autonomous system detects malfunctions and tries to fix 

them on its own, tinkering with all it has at hand. Internal 

innovation happens when a new type of malfunction is fixed. An 

interesting aspect of this process is that what causes a new type of 

malfunction can be the result of the system’s interaction with a 

new environment. Therefore this immune response mechanism 

functions as an adaptive drive. The system remembers the solution 

for future use and with quicker response. It has innovated with 

respect to its previous capabilities, and learns from this action. In 

this sense the system has adapted. 

KEYWORDS: Interaction, innovation, immunity, 

imperfection, adaptation, evolution, repair mechanisms. 

1. INTRODUCTION

 

A hurdle in the construction of an autonomous system is to 

find and implement design that would allow them to 

function in changing environments. The system has to 

operate according to its tasks and at the same time deal with 

unexpected situations that happen within its territory, for 

which it has no preset way to find solutions. If the system 

begins to malfunction while interacting with a new 

situation, it should be able to recognize that there is a 

problem, be involved in diagnosing the problem, and try to 

implement a solution. 

Beyond its ability to carry out tasks, an autonomous 

system has to change in response to learning from 

unexpected situations. The system has to innovate at least 

with respect to itself. It has to be adaptable. This is one 

measure of its intelligence given the environment in which 

it is meant to perform. 

Our own natural intelligent systems are a source of 

inspiration for designing autonomy. We appear to have two 

rather distinct systems tailored for different sorts of tasks. 

Our brain/nervous system is more for navigation and 

exploration. Llinás described our feeling of self as a way to 

help us have a sense of location in the maps of the world we 

create. This self we create helps us move as safely as 

possible in our environment [1]. Perhaps the most critical 

function of our brain is to help manage our body’s 

interactions with the world. 

Our immune system’s task is more internal. It has to 

keep the body working well as it moves and interacts in its 

changing environment. Its function is mostly to manage 

internal interactions. Not surprisingly, its architecture is 

quite different from the nervous system. The architectures 

of these two intelligent systems are based on their tasks. We 

use both at the same time in a loosely coordinated way. 

In this paper I will focus on intelligent features of our 

immune system that may be applied or emulated in the 

design of constructed autonomy. Immune mechanisms can 

be a vast source of inspiration for the design of autonomous 

systems for dynamic environments. Our natural immune 

system is an intelligent system in its own right, along with 

our brain/nervous system. It uses special procedures of its 

own that we can try to imitate to some extent in the design 

of artificial intelligence features. As we examine these 

features, it helps to keep in mind that they are not meant to 

replace existing architectures. What they could do is 

increase the robustness of current designs and therefore 

enable them to be more interactive and useful. We also 

have to realize that the drawback of such features is that 

they increase the complexity and cost of the system. The 

ultimate implementation of immune features would then 

depend on a balanced approach to the task at hand. This 

balance includes resources available and cost. 
2. MODELS OF IMMUNITY

Alexander Tarkanov has done extensive work in 

mathematical modeling of immunocomputing. To help 

conceptualize this field, he first groups the various 

approaches to the construction of intelligent systems into 

two directions. One uses generative grammars and logic. 

The other is based on biological models. In this second 

approach there are three main directions of research: neural 

networks, cellular automata, and genetic algorithms [18]. 

Tarkanov indicates that his work belongs to a fourth 

direction that is starting to gain momentum: artificial 

immune systems (AIS), which includes immunocomputing 

[2]. 

Classifications come in all shapes and forms. This one 

helps locate AIS within the many areas of AI. In this paper 

I will review selected features of our immune system 

implemented in autonomous systems that operate in 

changing environments. I will argue that these features of 

the immune system help it adapt when confronted with new 

situations. In other words, these features are engines of 

innovation. 

Models of the immune system fall within the range of 

two main philosophies. One presents immunity as a battle. 

The immune system detects and seeks to destroy intruders. 

The second view is that the immune system is an ensemble 

that seeks to stay in balance. Its response to whatever 

affects it is a rebalancing that in fact becomes adaptation 

[3]. 

In the first view, the immune system is inflexible in its 

identity. A successful cure leaves the system as it was 

before the attack, except that now it retains a memory of the 

aggressor and will be better able to respond to a similar 

attack in the future. This perspective goes back to the 

1950’s when immunology became known as the science of 

the self-nonself discrimination. 

Stephanie Forrest and her group at the University of 

New Mexico developed a system of negative-detection of 

intruders in computer systems. Algorithms search the 

computer system for possible changes in specific areas. 

Then the system tags the change as an intrusion, deals with 

it, and retains a memory of the event for quicker future 

response to a similar intrusion. The immediate practical 

goal of this approach is to give computers a level of selfprotection from unexpected viruses and other harmful 

intrusions. Forrest and Hofmeyr acknowledge that 

immunology is more than self-nonself discrimination. In a 

footnote to "Immunology as Information Processing" [4], 

they note, however, that their approach is an 

oversimplification. There are harmless intruders that the 

immune system tolerates, and there are also immune 

reactions against non-intruding self-cells as in some cancers 

and autoimmune responses to what should not be perceived 

as an attack. 

The model that Forrest and Hofmeyr followed is nonadaptive. Although the environment can be dynamic and 

the attacks novel, the negative-selection response is always 

the same. Nonself is detected and attacked to destroy it. 

This is a war type model. It hinges on the destruction of the 

enemy. It is non-adaptive because in the end, there is 

nothing to adapt to. Nevertheless, the algorithm of negativeselection is considered a milestone in the development of 

AIS, and rightly so given the enormous complexity of 

immunity [1]. 

Tarakanov and Dasgupta used the approach of selfnonself recognition to develop a formal model of an 

artificial immune system as a highly distributed learning 

system [6, 1, 7]. They developed a very simplified artificial 

formal protein that includes torsion factors as a way to 

model the shape matching that is one tool for identifying 

non-self intruders. This is their attempt to model the fact 

that we have tagging proteins that learn by matching shapes 

with intruders and binding where a match occurs to act as a 

tag. Tarakanov and Dasgupta then added reproduction and 

death of the formal proteins to expand their search function. 

But this mathematical formalism has not yet been tested 

out. The problem is that it also needs an environment to 

function and evaluate the performance. In other words, it is 

not sufficient to formalize the search proteins; the 

searchable environment has to be also formalized. Or at 

least a suitable interface has to be developed to interact with 

the environment. This is still a difficult task to achieve. 

Dasgupta and González compared negative selection 

and positive selection algorithms in the self-nonself 

approach to intrusion detection in computer networks [8]. 

They concluded that elimination of what is different is 

easier to implement and requires fewer resources than 

checking positive membership in the self-group. The reason 

is that positive selection is far more memory intensive, at 

least in the model they developed. The notion of self was 

not an abstraction but the membership itself. To detect 

membership in the set, it is necessary to compute the fitness 

with respect to each member of the self-set and a degree of 

abnormality is established. There is self-recognition if the 

abnormality is smaller than a set limit. Negative recognition 

is done, however, with respect to a single standard, and 

therefore is easier to implement but if offers less flexibility. 

It is interesting that in this approach non-self is identified as 

novelty and eliminated. I will explore how to take 

advantage of novelty. Rather than eliminate it, it can be 

used for learning and adaptation to the novelties of a 

changing environment. In this way a system can innovate. 

Melanie Mitchell developed with Douglas Hofstadter 

an adaptive model based on analogy making [4, 17]. 

Although it predated the rise of AIS, it has a feature that 

can be applied to the construction of an immune system, 

and that is the development of a balance between 

exploration and attack. She based this on John Holland’s 

concept of a balance between “exploration and 

exploitation” [5]. She notes that the immune system 
exploits information from attacks and allocates resources, 

but it also continues to explore possibilities that might 

happen by continuously upgrading an enormous repertoire 

of cells used in recognizing intruders and initiating immune 

responses. In an actual response, the immune system tinkers 

with the intruder using detector or tagging cells until 

gradually the response becomes increasingly focused. Her 

constructed system uses random combinations and random 

mutations to perform such exploration and tinkering. This is 

in fact a blind search. It is feasible in small domains, but 

entirely random responses simply would take too long for 

our immune system to work consistently. Mitchell imagines 

that the next step is the development of more tailored 

explorations. What is needed is more preliminary 

interaction between the unknown organisms and the 

immune system to reach some sort of cooperative balance. 

After all, the most successful intruders are those that don’t 

destroy the system, because they would also destroy 

themselves in the process. 

At the opposite end of the immunology spectrum is the 

systemic model best represented by the initial work of 

Francisco Varela and then modified in collaboration with 

Antonio Coutinho. Varela did not follow the self-nonself 

procedure of identification of foreign agents invading the 

body. Instead he considered the body a semiotically closed 

system whose task it to maintain itself in balance. In such a 

system there are no intrusions, only perturbations to its 

balance. So the immune reaction is not to a foreign agent as 

such but to a disturbance. The striking difference between 

this model and the self-nonself one is that it does not follow 

the war metaphor. Instead it follows an interactive and 

cooperative approach. The system reacts to the disturbance 

and affects not just the agent but also the entire system. 

This requires the tinkering that Mitchell had noted, and the 

gradual learning of the situation in search for a solution. In 

this process, it does not matter what happens to the foreign 

agent as long as the system regains its balance. In other 

words, the agent may be incorporated into the system 

somehow, as long as it does not continue to unbalance it. 

But now the agent itself may be part of the new balance. In 

this way, the system adapts and evolves while following its 

task of maintaining a balance. 

I can think of two examples to give a sense of how this 

systemic approach works. One is the population dynamics 

in U.S.A. We see that immigration rules act as a regulatory 

system for the country’s semi-permeable borders. 

Immigrants may or may not enter according to rules, and 

the systemic reaction is not always one of elimination. 

Instead, the cultural disturbances of immigrants are 

transformed into the fabric of the country while at the same 

time the country readapts to the variations. This leads to the 

gradual series of adaptations that make the U.S.A. a selfsimilar nation yet at the same time one that has striking 

cultural differences from what it was before. 

A second example is the Michael Crichton’s 

technofiction novel The Andromeda Strain. An unknown 

strain from outer space has infected a small town and with a 

destructiveness that surpasses a plague. The zone is isolated 

and authorities try to figure out what to do to contain the 

threat, learn about it, and in the end eliminate it. Nothing 

seems to work. Towards the end, the containment perimeter 

is breached. An aircraft flies too low and undoubtedly 

carried the strain with it to its landing site. But surprisingly, 

no damage results. It turns out that the strain has mutated 

gradually into a form that is harmless to its new 

environment and is able to coexist on Earth. What Crichton 

showed is how the strain itself adapted to the new 

environment in a sort of highly intelligent systemic 

immunity in reverse. But we gather that this mutation 

responds to the devastation that the strain caused in its 

original form. In other words, the strain mutated from a 

non-cooperative configuration to a cooperative one, and we 

can imagine that it did not vanish but coevolved and thrived 

instead quietly in its new form. 

3. IMMUNITY, ADAPTATION, AND 

INNOVATION

Let’s consider balanced interactions in which there is 

possible co-adaptation of foreign agents, internal 

disruptions, and a system. Here conflict may be enhancing 

in some ways, and foreign agents, rather than being erased 

or assimilated, become contributors to the adapted fabric of 

the dynamic system. 

What I would like to explore here is how immunity 

functions in this situation. This leads to the question of 

innovation, because the immune system has to deal with 

situations it did not encounter before and must balance 

them somehow without destroying itself. The solution 

would be an innovation for the system since it carried out a 

new procedure and since it recognizes the procedure as new 

and can implement it quickly the next time a similar 

situation happens. 

Traditionally, intrusions of foreign agents and internal 

disruptions are imperfections in the system and called for 

corrections to restore the original sense of perfection. But 

now we know that such state of perfection can only be 

defined in a negative way and this leads to a non-interactive 

architecture, inflexible, and not suitable for operating in a 

changing environment. 

As we saw before, a positive definition of self or 

system is redundant, in the sense that it hinges on 

membership [8]. But this is the type of sense of self we 

need because it is flexible. I can change in a gradual and 

somewhat controlled way. Membership hinges on a preset 

fuzzy distance to what we can imagine as the center of mass 

of the existing membership set. As new members join the 

set, the center of mass shifts. This in turn changes 
membership acceptance. We can say that the system’s self 

adapts to its environment this way. 

If we place this dynamic sense of self as a model 

within the elementary loop of function, or ELF architecture, 

that Meystel and Albus developed [9], then we have the 

foundations for what could be the primary controller of an 

autonomous system capable of operating in a changing 

environment. 

This is where immune concepts come in. Imagine the 

low resolution, control ELF as a cell with semi-permeable 

boundary defined by its membership class and the fuzzy 

measure that allows new members to enter the cell. 

Constructed immune mechanism must keep such self in 

balance internally and also with respect of the rest of the 

autonomous system that the ELF controls. This immune 

system then has to work within the top ELF, so to speak, as 

well as throughout the entire autonomous system, to make 

sure that shifts in self-identity at the top do not wreck the 

system. This should be achieved through immune 

mechanisms interacting through loops [10] at two levels: 

within the top ELF cell and throughout the entire 

autonomous system. Perhaps there could be a third loop 

involving the autonomous system and its environment. 

In previous works I proposed that imperfections could 

fuels innovation through compensatory and repair 

mechanisms that function like an immune system of the 

imagination [11, 12]. Innovation could then be pictured as 

stemming from an immune mechanism coupled with a 

selection process and a well-tuned construction system. 

What we need to do is not filter out novelties that penetrate 

the control ELF, but somehow gauge them, and incorporate 

what works by turning it into a system innovation. As 

Dasgupta and González [8] noted, this requires more 

resources, particularly memory, but is also more effective 

than using the negative approach that eliminates all novelty. 

If we try to incorporate immune capabilities into an 

autonomous system, the previous review suggests that to 

behave as an adaptive system in a changing environment, it 

would need special features in its architecture. 

1 – It would need at least one control ELF that serves as 

self. As suggested before, the self-set uses a fuzzy measure 

for positive recognition of membership. The autonomous 

system is launched with an initial self-set. As the system 

interacts with the changing environment, it becomes 

infected, so to speak. The control ELF takes in new selfelements that fall within the fuzzy measure for positive 

recognition of membership. This process is Building 

blocks of elementary functioning loops that have memory 

and remodeling capacities. Neural nets can produce these 

capacities. A layered network of such blocks so that there 

are external and internal inputs at all levels of the system. 

2 – To simplify the complexities of immune interactions, 

the system should use encoding or tagging mechanisms 

[13]. This helps integrate the many layers, hierarchies of 

ELFs and other mechanisms of the system. Such tags are 

like names in a language. They abstract features and allow 

operating directly on the tags. As Meystel indicates, this 

process of generalization and representation helps establish 

links among different levels of resolution in the system’s 

architecture. It also reduces the complexity of the system 

because it can operate on compressed representations rather 

than on originals. The original can be decompressed when 

needed by calling the tag. 

3 - Network loops can synchronize the entire system so that 

it can interact in various ways, especially in the formation 

of higher-level memories, remembrances, and remodelings 

[10]. For this we have the neurological model that Edelman 

calls reentry, which is the synchronous firing of widely 

dispersed neurons in the brain. Feedforward and feedback 

signals produce such reentry loop. We also have examples 

from the immune system. The intrusion into the system of 

infections puts into motion feedforward and feedback 

processes throughout the entire immune system until some 

final state is reached. The immune system acts as a network 

that interacts with the infection, learns from it, and 

readjusts. If all goes well, the system learns from the 

incident and is better prepared to deal with similar ones it 

might encounter. 

4 - Redundancy [13]. This enhances the capacity of 

subsystems for self-repair or compensation. Meystel 

describes redundancy as excess in a system. He notes that 

although such excess may appear as a waste of resources, it 

is necessary for exploration. He links redundancy with a 

certain playfulness that operates in the excess. He links it 

also to a sense of desire or emotion that can serve as a 

vague guide in exploring by using excess resources. 

Solé et al note that redundancy should be understood 

not as an excess of the same resources but of variant 

resources [16]. Edelman called this “degeneracy” [19]: 

structurally different components can yield similar results. 

Solé indicates that degeneracy is deeply related to tinkering 

in evolution in the sense that different systems can perform 

similar functions and therefore can be made available in 

non-linear ways to yield solutions that open the possibility 

of divergence of architectures. In a changing environment, 

the possibility to carry out a similar task using different 

architectures is a very robust and adaptive feature, since 

with changes new architectures would be more suitable to 

the shifting context and yet the original function can still be 

performed. Although I imagine that the original task would 

also be adapting. This dynamics is closely related to neutral 

development and play. 

An adaptive autonomous system depends to some degree on 

being enabled to carry out the following two processes: 
1 - Neutral development [14, 15]. This is a stand-by mode 

of search and development for no immediate use, but one 

whose task is to prepare the system for future imbalances 

by giving it more diversified resources. 

Motoo Kimura is the architect of the notion of neutral 

evolution and he applied it initially at the molecular level. 

He notes that the overwhelming majority of changes in 

nature are not caused by natural selection but “by random 

fixation of selectively neutral or nearly neutral mutants” 

[14]. He adds that “although such random process are slow 

and insignificant for our ephemeral existence, in the span of 

geological times, they become colossal.” 

In constructed autonomous systems it is possible to 

speed up neutral search when necessary. This would be 

possible at moments the system is rather inactive and 

therefore has more resources available. Lobo, Miller, and 

Fontana picture neutral search as an aimless process that 

happens within a landscape of solutions that have optimal 

peaks [15]. Imagine a static environment for an autonomous 

system. The system has interacted with the environment 

and provided optimal solutions for the various regions of 

the landscape. After this optimal adaptation, the system has 

nothing else to do. It is stuck, so to speak, with the peaks. 

Should the landscape change, the system would have to 

start all over again. In neutral mode, the system does not 

rest even if the landscape remains static. The system roams 

around the peaks and develops imperfect solutions. 

Viability rather than optimization is what counts. In this 

way, the autonomous system engages in neutral 

development that later can impact its behavior when 

confronted with unexpected situations, and make it simpler 

to find new solutions since it has already tested out many. 

What fuels all this neutral development work at a time of 

system leisure is play. 

2 - Tinkering and play [12, 16, 20, 21]. Solé et al noted that 

tinkering is an important process of evolution, and therefore 

of adaptation. They describe tinkering as the re-use of 

different parts of a system in order to achieve a given 

function. Those different parts are put to novel uses to have 

them do together what they were not really designed to do. 

Tinkering then is an imaginative use of resources, not really 

in optimal ways, but as back-ups or alternatives. This 

contributes to the robustness of the system because 

redundant subsystems evolve through tinkering, and they 

may come in handy one day when all normal channels fail. 

Internal tinkering can give a system more protection against 

random failure. This process is a clear example of neutral 

search. 

Tinkering is a form of play restricted to a specific set of 

elements at hand. Play is more general. Piaget offered 

perhaps the most concise model of adaptive play as pure 

assimilation. That is to say, the player interacts and absorbs 

aspects of the world without changing its action schemata. 

The question is how to implement such concept with 

autonomous systems. Let’s divide the process into two 

components. One is the unchanging schemata that provides 

equal weight to all choices available. The other is the 

individual player with preferences that mark individuality 

and that would prefer certain choices without clear 

justification beyond personal preference. Combining these 

two aspects, the simplest technical way to define play that I 

can think of, is to model it as a random search with 

preferences. 

The practical advantage of having a play mechanism in 

an autonomous system whose tasks include exploration in a 

changing environment, is that a narrowed random search 

can save a great amount of testing and memory. The 

preferences arise from the interaction of the self with the 

local environment. It is a situated preference relevant to the 

moment. This is the engine that drives neutral development 

as well as recombinant process of exploration. It also helps 

the system with the overall capacity for self-repair or 

compensation. The system’s degree of play can be 

controlled through resource allocation given its current state 

and task. This can be a control mechanism weighed 

internally. It could also be weighed externally but this 

reduces the autonomy of the system. 

4. CONCLUSION 

Natural immune mechanisms are a source of modeling 

inspiration for the design of autonomous systems capable of 

operating in dynamic environments. The construction of 

AIS processes is just starting. Most work is still at the 

conceptual level. We saw that natural immunity is an 

intelligent, learning ensemble of interacting mechanisms, 

and has a strong adaptive function. Modeling immunity can 

help make adaptive autonomous able to function in 

changing environments. We noted that to begin to tap this 

potential the AIS must be designed not in a negative 

reactive way following the war model, but in a positive way 

that is more like balanced trade across differences. As 

Holland noted, an adaptive system has to be able to exploit 

as well as explore. We saw that immunity is the part of the 

system that can assist with exploration as well as help 

maintain the system’s integrity so that it can continue to 

carry out its tasks. 

I focused specifically on two processes associated with 

immunity that could be implemented in autonomous 

constructions, although their importance is only indirectly 

related to achieving assigned tasks. These processes are 

neutral search, tinkering, and play. All are essential parts of 

natural immune systems, but are difficult to implement in 

constructed systems, and may seem to be too much idle 

luxury given the potentially high cost of making them work 

well. 

But in the research and development phase, when 

discovery outweighs implementation, and when our 

imagination is freer in the use of resources, we do have 
more room to play. We can tinker with models and 

architectures in unexpected ways as long as dogmas don’t 

hold us back and we keep to the task of allowing innovation 

to happen. In the case of immune features, they might lead 

to surprising integrations with architectures we already 

have. Perhaps by enhancing the capacity of constructed 

systems to engage in neutral tinkering and play we may 

render them more curious and, paradoxically, more robust. 

This enactment of interaction may well mark the transition 

to a new generation of autonomous systems able to explore, 

innovate, and adapt while carrying out their tasks. 

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Intelligence ≠ Autonomy ≠ Capability 

J. P. Gunderson, L.F. Gunderson 

Gamma Two, Inc. 

{jgunders, lgunders}@gamma-two.com 

ABSTRACT 

In recent years, there has been a tendency to confuse the terms 

Intelligence, Autonomy, and Capability. In this paper we present 

the viewpoint that intelligence and capability are independent. 

These two factors describe an orthogonal design space that places 

upper bounds on the autonomy of the intelligent system. This 

design space for intelligent systems is illustrated by describing 

existing intelligent systems (some artificial, some natural) which 

demonstrate discrete points in the design space. Further, exemplars 

from biological systems indicate that there are natural constraints 

within the design space for intelligent systems, which suggest the 

need to balance the intelligence and capabilities of the designed 

systems. This design space is used to construct guidelines for the 

development of intelligent, capable, and autonomous systems. 

KEYWORDS: Intelligence, Autonomy, Capability, Intelligent 

Systems, Robotics, Autonomous Systems.

1. INTRODUCTION

In recent years, there has been a tendency to confuse the 

terms Intelligence, Autonomy, and Capability. In this paper 

we present several arguments, drawn from research in 

biology, cognitive science, artificial intelligence, and 

psychology, that demonstrate that these concepts are far 

from equivalent. Further, we propose that, while these 

concepts are clearly related, they may be orthogonal. If this 

orthogonality can be demonstrated, then it could be 

leveraged to allow researchers to correctly categorize both 

the requirements of complex tasks, and the types of 

intelligent systems that are needed to achieve these tasks. 

In this paper we present the viewpoint that intelligence 

and capability are independent – that one can have 

significant intelligence and lack capability, or vice versa. 

This is a critical design concept for engineers and scientists 

involved in the design and deployment of intelligent 

systems, since the design problem requires the careful 

application of the correct resources to solve specific 

problems. Autonomy is presented as an ability that is 

bounded above by the independent terms of intelligence and 

capability, however below this boundary, autonomy is 

shown to be conditionally independent as well. 

This design space for intelligent systems is illustrated 

by describing existing intelligent systems (some artificial, 

some natural) which demonstrate discrete points in the 

design space. These exemplars are further used to extract 

design criteria for the needed levels of intelligence and 

capability, and the degree of autonomy which is necessary 

for an intelligent system to achieve its goals in its target 

environment. 

2. DOMAIN

Before addressing the working definitions, it is necessary to 

develop a context. In this paper, the domain is considered to 

be goal directed behavior in dynamic and uncertain 

domains. Goal directed means that the intelligent systems 

deployed into these domains have goals that need to be 

achieved. This means that the systems are not behaving 

randomly, rather they are developing action sequences or 

selecting behaviors to change the state of the environment, 

and acting on these action sequences. The environment is 

dynamic, in that it is changing over time, in ways that are 

independent of the actions of the intelligent system. The 

intelligent system’s perception of the environment is 

uncertain and the results of the actions taken by the 

intelligent system are non-deterministic. 

These characteristics of the domain place significant 

demands on any intelligent system. In this domain, the 

intelligent system can only achieve probabilistic goal 

satisfaction; there is no guaranteed optimal performance. 

However, any system deployed in the real world must be 

able to deal with these problems. 

3. INTELLIGENCE AND CAPABILITY

In order to have a common framework for discussion, it is 

necessary to have at least a working definition of the terms. 

While it would be nice to have precise definitions, these 

working definitions are meant to be tools for analyzing 

systems, not an absolute characterization that divides the 

world into classes. 

In the area of measuring the performance of intelligent 

systems, a common approach is to measure the probability 

of goal satisfaction as a measure of intelligence. However, 

this results in confounding the effects of intelligence and 

capability. This confounding effect has contributed to the 

confusion of these two concepts, which has caused 

problems in the design and development of intelligent 

systems. The following sections present definitions for the 

terms intelligence and capability. 

3.1 INTELLIGENCE 

Intelligence has defied formal definition for as long as the 

concept has existed. There is a general consensus that 

intelligence is related to being able to solve problems, or to 

produce things that are of value to the society [1]. This 
concept circles around the core idea that an intelligent 

system has the ability to achieve goals within an 

environment that is dynamic and uncertain. While 

intelligence is often characterized as a single entity, (e.g., 

Spearman’s general intelligence, g), this theory has been 

criticized on a number of grounds [2]. Thomson argued in 

1939 that there was no evidence that g represents any 

underlying structure in the nervous system of humans [3]. 

While Spearman proposed a two factor analysis, a 

combination of g and a collection of specific factors (s), 

recent work has proposed anywhere between seven and one 

hundred and fifty separate factors [4]. 

In the transition from natural intelligence to artificial 

intelligence, there is less emphasis on deriving the structural 

factors and more emphasis on the functional aspects. In part, 

this is due to the constructive nature of artificial intelligence 

as an engineered product, which is designed to meet specific 

requirements. Therefore, for this paper, the focus is on 

measuring intelligence via factor based performance metrics 

– how well does the intelligent system develop solutions to 

problems in a dynamic and uncertain environment. This is 

more closely allied with Newell and Simon’s “intelligence 

as problem solving.” [5] Albus and Meystel have proposed 

defining intelligence as “the ability to behave appropriately 

in an uncertain environment,” where appropriate behavior 

will maximize the likelihood of goal satisfaction [6]. 

A critical aspect of intelligence is that it is based on the 

ability to determine or develop a good solution to a 

problem, not necessarily in the ability to execute it. In the 

human realm, a skilled mechanic, who can quickly and 

accurately diagnose a complex problem, does not become 

less intelligent because an injury prevents her from 

physically manipulating the wrench needed to execute the 

repair. Nor does she regain intelligence when the injury 

heals. Any working definition of intelligence must not fall 

into the trap where breaking one’s leg makes one stupider. 

The definition used here is: 

Intelligence: the ability to determine behavior 

that will maximize the likelihood of goal 

satisfaction in a dynamic and uncertain 

environment. 

This definition meets the criteria that an incidental 

change that impairs the ability of the system to execute the 

behaviors does not alter the intelligence of the system. 

Clearly however, the ability to successfully execute the 

appropriate behavior does affect the system’s ability to 

satisfy goals in the real world. This successful execution is 

the capability of the system. 

3.2 CAPABILITY

Execution capability has been less studied. Capability 

describes the ability of the intelligent system to successfully 

execute behaviors. An intelligent system may be able to 

correctly determine a valid course of action to achieve a 

goal, but be incapable of executing that course of action, 

while another system (such as a teleoperated robot) might 

be incapable of developing any ‘intelligent’ solution, 

however, given one, it can execute it and respond to minor 

failures during execution. An example of this would be our 

injured mechanic. She can correctly determine both the 

cause of a problem and the necessary repairs, but lack the 

capability to execute the repair. Her assistant, who may not 

have the intelligence or experience to solve the problem, 

can follow her instructions to effect the repair. The 

capability of her assistant does not imply intelligence. 

Capability: the ability to successfully execute 

behaviors or actions in a dynamic and uncertain 

environment. 

There is one thing that should be noted about this 

definition. Unlike intelligence, capability is not goal 

oriented. This means that doing the wrong thing 

successfully does not imply reduced capability. However, 

selecting the wrong behavior to execute does imply reduced 

intelligence. 

3.3 INDEPENDENCE OF INTELLIGENCE AND 

CAPABILITY

No attempt will be made in this paper to present a 

mathematical proof of independence. Rather, examples of 

intelligent systems which span the range of intelligence and 

capability will be presented. It is clear from the working 

definitions presented above, that intelligence is defined by 

the determination of behaviors, and has no definitional 

component related to execution. Likewise, capability is 

defined without any reference to the appropriateness, or 

correctness, of the actions, and is dependent only on the 

successful execution of the required actions. 

Consider the example of vacuum cleaning robots and a 

two story home. The vacuum cleaning robots are available 

in several versions. They can be intelligent, with detailed 

maps of the furniture, and an understanding of traffic 

patterns; or they can be simple reactive systems that bump 

into things and vacuum at random. Second, they can be 

equipped with simple wheels, or they can be equipped to 

climb stairs as well. The goal is to keep all the carpets in the 

home clean. 

Table 1 - Goal Satisfaction for vacuum cleaning robots 

 Stairs 

 Low High 

Intelligence Low 0.25 0.50 

 High 0.50 1.0 
In this case, the intelligent vacuum cleaners do a much 

better job of cleaning the corners, and getting the hightraffic areas, so the goal satisfaction is higher for the areas 

that they can reach. The stair climbing robots can reach 

more of the carpets, regardless of how good a job they do, 

so the goal satisfaction is higher overall. In effect, for all 

four of these robots goal satisfaction is a function of both 

intelligence and capability – but high intelligence can exist 

independently of high capability, and vice versa. This 

implies that: 

g = f (c,i), [1] 

where g = goal satisfaction, 

 c = capability, and 

 i = intelligence. 

4. RELATIONSHIP OF AUTONOMY TO 

INTELLIGENCE AND CAPABILITY

In the previous section, working definitions for intelligence 

and capability were presented. These definitions offer 

several advantages in that they are independent, measurable, 

and are derived from the common usage of the words. As 

mentioned in the introduction, these are intended as tools to 

analyze systems, not necessarily to characterize them. 

In this section autonomy is addressed, building from 

the previous definitions. The intent is to delineate the scope 

and relationships between these terms. 

4.1 DEFINING AUTONOMY

The concept of autonomy, like that of intelligence, is 

controversial in the artificial intelligence and robotics 

communities. However, it is somewhat less controversial in 

everyday usage. According to one dictionary definition (in 

all cases the dictionary used is the 1969 American Heritage 

[7]). Autonomy is defined as: 

Autonomy: 1.The condition or quality of being 

self-governing. 2. Self government, or the right 

of self-government; self-determination, 

independence. 3. A self-governing state, 

community, or group 

The common term in all these definitions is selfgoverning or self-government. Clearly, to be autonomous is 

to be able to govern oneself, but what does this mean when 

applied to an intelligent system? 

Govern also has an everyday meaning, which, while not 

commonly applied to a robot, has direct applicability to 

intelligent systems. 

Govern: 1. To control the actions or behavior of; 

guide; direct. 2. To make and administer public 

policy for (a political unit); exercise sovereign 

authority in. 3. To control the speed of magnitude 

of; regulate. 4. To keep under control; restrain. 5. 

To decide; determine. 

And the list goes on to grammatical uses. However, the 

clear thread in the definition of govern is the ability to 

decide and implement decisions. By extension, the sense of 

self-governing is the ability to decide and implement 

decisions for and by oneself. Hence, autonomy is the ability 

of a system to make choices and enforce its decisions. 

While this is consistent with the common usage, and has 

been supported by many researchers, this definition can be 

considered to conflict with a definition that limits the 

autonomy to be with respect to some goal or task assigned 

by an outside agency [8]. This definition addresses the issue 

raised by researchers such as Alan Schultz that a truly 

autonomous robot would be sitting on a beach somewhere, 

drinking motor oil, not slaving away on some human 

assigned task [9]. 

As an interesting side note, the etymology of govern is 

from the Greek kubernan: to steer, guide. This is the same 

root work that gives us cybernetics, coined by Norbert 

Weiner to refer to the theoretical study of control systems. 

In effect, an autonomous intelligent system is simply one 

that has the capability to control itself, to make decisions 

and implement those choices. Where, then, do these choices 

come from? Certainly, if the system is incapable of 

generating multiple options to achieve a goal, it cannot 

decide which behavior to undertake. With no viable 

behaviors, or a single solution to a problem, there is no 

choice – and therefore no ability to decide. While a system 

that can produce fifty possible goal satisfying solutions may 

be more intelligent that one that can only produce ten such 

solutions, it has no more autonomy. A system that can 

successfully execute more complex behaviors may be more 

capable than another, but that does not make it more 

autonomous, if an outside agency can override the chosen 

behavior and force an alternate behavior. 

4.2 ESSENTIAL RELATIONSHIP

Notice there is nothing in the definition of autonomy 

that addresses the quality of the decisions made by the 

autonomous system. An entity can be autonomous and 

stupid, or be autonomous and smart. A system can make 

good decisions and implement them poorly, or implement 

them well. Autonomy is independent of intelligence (the 

ability to select appropriate behavior) and independent of 

capability (the ability to successfully execute an action or 

behavior. 

Given the definition that autonomy is simply the ability 

of an entity to decide its own behavior and to execute that 

behavior, how does that relate to an intelligent system such 

as a robot? One critical factor is that the system must have 

the ability to select between options. If a system has no 

choice in the behaviors that it exhibits, then it cannot be 
autonomous. In addition, if the choices made by the system 

can be overridden by an external agency, then the system is 

not autonomous. If a system has options to select from, and 

the ability to select and implement an option, then it is 

autonomous. Thus, a bi-metallic strip thermostat has no 

autonomy. The user selects the set point, and physics define 

the only possible action at any time. The thermostat is not 

free to say “Well, I know my set point is 72 degrees 

Fahrenheit, but I won’t kick over until it gets down to 68.” 

On the other hand, a simple random walk robot, with no 

goals except to keep moving, may have complete autonomy 

in the choice of direction and distance, and can 

autonomously fall down a staircase if it selects the wrong 

option. 

Since the inability to produce a course of action 

precludes its use, and the inability to execute a course of 

action prevents it from being valid; it follows that 

intelligence and capability act as upper bounds on the 

autonomy of a system. However, while these two capacities 

limit the maximum autonomy of a system, below this limit 

the system can have a much or as little autonomy as the 

designer (in the case of an artificial intelligent system) 

allows. 

Based on the definitions, it seems that intelligence and 

capabilities define an action space, and autonomy is 

bounded by this space (See Figure 1). 

Figure 1: Effect of Intelligence and Capability on the 

range of autonomy. As intelligence and capability 

increase, the range of available options increase. The 

system can be autonomous, in which case it can select 

from these options. Or the system may not be 

autonomous, in which case its action space collapses to a 

single point for any goal/environment combination. 

The available actions may be discrete options such as 

‘open a door’ or ‘send an email’. In the case of a mobile 

robot selecting a new heading or selecting a distance to 

travel the options may be drawn from an effectively 

continuous range. In terms of autonomy, it does not matter 

how many options are available, or even if there are an 

infinite number of options. All that matters is that there are 

options, as defined by the intelligence and the capabilities of 

the system, and that the system can select between them. 

This leads naturally to the following question: Given a 

fixed system that can produce multiple feasible solutions to 

one problem, but can only produce a single solution to 

another problem in the same domain, is the system 

autonomous in the former case, and not autonomous in the 

latter? 

Unfortunately, this leads to a typical white box versus 

black box problem. What if the system has multiple options, 

but always selects the same one? How does this differ from 

a system that only has that single behavior available to it? Is 

one autonomous and the other not – and how can one tell 

from the outside? This is clearly another variation on the 

‘strong’ versus ‘weak’ question that has plagued artificial 

intelligence, cognitive science, and philosophy since their 

inceptions. The focus of this paper is not to answer such a 

complex conundrum, but to look at the implications of the 

relationship between autonomy and intelligence and 

capability. 

Simply put, if the system cannot generate options for 

behavior, then the autonomy of the system is compromised; 

if the system cannot select between options, then the 

autonomy of the system is compromised; and if the system 

can select one of several options, but the execution of the 

option is controlled by an outside agency, then the 

autonomy is compromised. Thus, given that the system is 

enabled to choose between options in the method of 

achieving its goals, the intelligence and the capability of the 

system act as bounds on the autonomy of the system. 

These two controlling factors, intelligence and 

capability, are independent in the abstract sense presented 

so far, and as such there are no constraints on either range. 

In theory, an intelligent system could be awesomely 

intelligent, yet totally incapable of achieving anything. 

Alternatively, a system could be a dumb as a box of rocks, 

yet have the capabilities of the most advanced robot ever 

imagined. These do not seem to be reasonable 

combinations. Examining of the existing intelligent systems, 

one does not see either extreme; rather the exemplars seem 

to be grouped with roughly balancing capabilities and the 

intelligence to use those capabilities. In the next section, 

examples of successful intelligent systems, deployed into 

harsh, dynamic, and uncertain domains are examined, 

drawn from biological systems. 

5. CONTROLLING FACTORS ON INTELLIGENCE,

AND CAPABILITY. 

Brains are expensive. [10] This means that, for a species to 

compete effectively, the increased intelligence must covey 

an increased survival advantage. In the following 

discussion, the relationship of intelligence and capability in 

natural intelligences will be examined. In order to talk 

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about animal intelligence, some discussion is needed of the 

types of intelligence. Animal intelligence has been 

partitioned into two major classes ‘menu-driven’ 

intelligence and ‘social’ intelligence [11]. 

The ‘menu’ in menu-driven intelligence does not refer 

to pull-down option selection in a Graphical User Interface. 

Rather it is based in the concept that biological organisms 

must eat to survive, and therefore those that can find and 

acquire more varieties of food (their menu) more effectively 

have higher survival rates. Since finding food in a 

dangerous, harsh environment is extreme problem solving, 

it drives the development of intelligence. 

Social intelligence is intelligence that is oriented 

towards communicating between individuals of the same 

species. The need for cooperation in hunting and defense 

require the ability to both develop team-based solutions to 

problems, and the associated skills of communication and 

maintaining group dynamics. This type of intelligence 

corresponds to Gardner’s Lingustic and social intelligences. 

These two types of intelligence will be treated 

separately. Since most organism can not describe their 

thought processes, all experimental evidence can show is 

the combination of intelligence and capacity. Starting with 

‘menu driven’ intelligence, it has been shown that 

distribution of foods acts as a stimulus for mental 

development in primates [12]. In effect, the need to 

cognitively maintain and track the recognition patterns, 

locations, acquisition techniques and risks of additional 

types of food, increases the cognitive demand on the 

system, and requires allocation of resources to cognition, 

hence more intelligence is needed. 

From this, it can be argued that in a highly competitive 

environment, any increase in intelligence that is not 

matched by an appropriate increase in capability could lead 

to the extinction of a species. The argument follows thusly. 

Let us consider two species in the same ecosystem. Both of 

these species are confronted with a new food source. One 

of the species uses its expensive brain power to construct a 

feeding strategy that it is capable of implementing. The 

other species constructs a feeding strategy that it is not 

capable of implementing. Clearly they have both exerted 

energy coming up with a solution, but only one has received 

a reward. In an evolutionary setting the species that came 

up with an implementable strategy has a major advantage. If 

the advantage is great enough, the losing species may face 

extinction. It is an interesting side note on the nature of 

biological systems, that the idea of an organism coming up 

with an unworkable strategy is almost unthinkable. This is 

the result of living in a harsh evolutionary system, where 

unsuccessful adaptations die out quickly. 

‘Social’ intelligence is one that humans are most 

familiar with. Certainly for our species, it may be one of 

the most important of the many types of intelligences. 

However, even in this type of intelligence, capability plays 

an important role. In order for this type of intelligence to be 

expressed, there must be both a sender with an idea and the 

capacity to transmit this idea, and a receiver with the 

capacity to receive the idea. By the same argument as 

above, if an organism spends energy developing a social 

intelligence, but it lacks the capacity to share, that organism 

will be out-competed by another organism that does not 

expend the energy to develop the social intelligence, or has 

the capacity to communicate the ideas. 

The notion of a species having a capability without the 

corresponding intelligence to use that capacity is hard to 

imagine. Try to envision a bird, for example, perfectly 

capable of flying, but unable to ‘think’ of flying away when 

a predator attacks. Such a situation could, perhaps, arise but 

it would not exist for very long under evolutionary 

pressures. Either a ground based species would out compete 

the bird, since it would not need to maintain the expensive, 

but useless, flight equipment; or a subset of the birds would 

develop the intellect to use flight, and out compete their 

stupid brethren, Clearly there are birds which do not fly, but 

those that are capable of flying have the intellect to use the 

capability when needed. 

For both of these classes of intelligence that have been 

established for animal minds, the intelligence and the 

capacity to use that intelligence must develop together. In 

the competitive natural environment, an imbalance between 

these factors would lead to competitive failure of the 

species.

Figure 2: Apparent range of the balance between 

intelligence and capability in biological systems. 

In Figure 2 is a rough representation of the existing 

biological intelligent systems, indicating the approximate 

parity between the capabilities of the system and the 

intelligence to use those capabilities. In general, the 

practical space is a close approximation to the abstract line 

where intelligence is precisely balanced by capability. 

However, there is a certain amount of variation as a result of 

the dynamic nature of biological systems. The region above 

the shaded area would correspond to species which had 

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intelligence in excess of their capabilities – resources 

invested in brains that could produce theoretic solutions to 

problems, solutions which could not be implemented with 

the existing capabilities. The region below the shaded area 

would correspond to species which had capabilities that it 

was impossible to figure out how to use. 

In an environment with resource limitations and a high 

cost for failure the angle of the shaded region is fairly small. 

However, in the design space of engineered intelligent 

systems it is possible to create systems which are not 

bounded by the harsh realities of life. Researchers routinely 

develop intelligent systems that have capabilities which far 

outstrip their intelligence, and, less frequently, systems are 

designed and built that have the intelligence, but lack the 

capability to achieve their goals. In the following section, 

examples of these systems are presented and some 

approximate design rules are suggested to attempt to 

balance the allocation of resources between capability and 

intelligence. 

5.1 LAW OF THE MINIMUM

In ecologic systems there is the notion that every species in 

an environment has a limiting factor. Leibig’s Law of the 

Minimum states that for every species, there is a single 

limiting factor that controls growth of that species in that 

system [13]. For desert species, the limiting factor is the 

available water. For a rain forest species, the limiting factor 

is the amount of sun energy. This paper argues that, in an 

autonomous system, the limiting factor will either be 

intelligence or capability. If intelligence is the limiting 

factor, then increasing the capability will not significantly 

improve the performance of the system or allow for greater 

autonomy. Conversely, if capability is the limiting factor, 

then increasing the intelligence will not yield a significant 

improvement. 

6. GUIDELINES FOR DESIGN OF AUTONOMOUS 

SYSTEMS

The current state of the development of intelligent systems 

abounds with examples where the intelligence is out of 

balance with the capabilities of the system. In many cases 

these systems are built as research tools, and the focus is on 

exploring only one of the two aspects. However, there are 

also examples of systems which are deployed into dynamic 

and uncertain domains and which are intended to achieve 

specific goals. 

The domain abounds with tele-operated systems where 

the capabilities of the system far outstrip the available 

intelligence. Systems which were intended as ‘force 

multipliers’ require three to five human operators. In part 

this is due to investing in capability rather than intelligence, 

and then falling back onto humans to do the ‘hard part.’ 

6.1 BALANCE CAPABILITY AND INTELLIGENCE

This will sound trivial, but if the system is not meeting its 

performance goals, determine what the problem is before 

attempting a fix. The reasoning above demonstrates that 

there are at least two possible, independent causes for 

reduced performance metrics. Either could be the limiting 

factor that is restricting performance. Fixing the wrong one 

won’t help as much as fixing the right one. 

Determine the limiting factor and address it, do not just 

throw more resources at the easy factor. In dynamic 

domains, where the intelligent system must deal with 

uncertainty, it is critical to limit the intelligence to that 

which is sufficient to solve the problem. Adding more 

capability to an intelligence limited system will show an 

improvement, but adding more intelligence will show a 

greater improvement. 

6.2 DON’T MAKE IT AUTONOMOUS, UNLESS 

THAT IS WHAT YOU NEED. 

Autonomy is problematic. If the system should be tightly 

controlled, then it needs to be tightly controlled. Autonomy 

is not a ‘magic bullet’ that will make an ineffective system 

work in a dynamic, uncertain domain. If the problem 

domain requires a specific response to specific inputs, then 

the designer must provide that mapping. Rather than adding 

autonomy, focus on building the correct mapping. 

If the system needs to be autonomous, and in dynamic, 

uncertain domains most successful systems must be 

autonomous[14], the intelligence and capability must be 

sufficient to support the autonomy. It is pointless to give the 

system autonomy if it has neither the brains nor the 

capability to use the autonomy successfully. In addition, 

making the system autonomous will not magically enable it 

to do its job. Autonomous stupidity is easy. 

7. CONCLUSIONS

One drawback to performance based metrics of intelligence 

is the confounding effects of intelligence and capability. No 

one would argue that a physicist such as Steven Hawking is 

not intelligent. Yet if he were put into a room and given a 

battery of intelligence tests, his physical disabilities would 

impact the measure of his intelligence – unless the tests 

were specifically designed to correct for the confounding 

effects. 

Recently, it has been the practice to measure the 

performance of intelligent systems and label the result 

‘intelligence’; however, the tests measure the combination 

of intelligence and capability. This has resulted in the 

merging of these two very important, very different terms. It 

is not uncommon to hear researchers say that capability is 

the same as intelligence. This paper is an attempt to clarify 

these two terms, so that they can be used to more effectively 

describe the complexities of intelligent systems. 
Intelligence is a cognitive process that allows a system 

to propose a viable solution to a problem or task. Capability 

is the ability to implement or execute a proposed solution in 

a dynamic, uncertain environment successfully. Both of 

these abilities are necessary for goal satisfaction and both 

are very difficult. However, by conflating the two terms, 

researchers run the risk of having a system that fails to 

achieve its goals due to insufficient intelligence, but 

increasing the capacity of the system in an attempt to 

improve it. This can be both fruitless and frustrating for the 

researcher. 

By keeping the concepts of capability and intelligence 

orthogonal, the system designer has a design tool that will 

allow her to determine the correct area to focus attention, 

and the correct type of improvements that will result in a 

better system. 

8. REFERENCES

[1] Gardner, H. Frames of Mind: The Theory of Multiple 

Intelligences Tenth anniversary edition, New York: Basic 

Books, 1993, ch.4, pp. 60-62. 

[2] Richardson, K, The Making of Intelligence, New York: 

Columbia University Press, 2000, ch.1, pp. 8-10. 

[3] Thomson, G.H. The Factorial Analysis of Human 

Ability, Boston: Houghton Mifflin, 1939, ch.1, pp.4. 

[4] Gardner, H., Kornhaber, M.L., and Wake, W. K. 

Intelligence: Multiple Perspectives, Fort Worth, TX: 

Harcourt Brace College Publishers, 1996, ch.3, pp. 70-75. 

[5] Newell, A. and Simon, H. A. Human Problem Solving

Englewood cliffs, New Jersey: Prentice –Hall, Inc., 1972, 

ch. 1, pp. 6–9. 

[6] Albus, J. S. and Meystel, A. M. Engineering of Mind, 

NewYork: Wiley Interscience, 2001, ch.1, pp. 6-7. 

[7] American Heritage Dictionary of the English 

Language, New York: American Heritage Publishing Co., 

1969. 

[8] Barber, K.S. and Martin. C.E., “Agent Autonomy: 

Specification, Measurement, and Dynamic Adjustment,” in 

Proceedings of the Autonomy Control Software Workshop, 

part of Autonomous Agents, 1999, pp.8-15. 

[9] Schultz, Alan, Panel Discussion, AAAI Spring 

Symposium on Interaction Between Humans and 

Autonomous Systems over Extended Operation, 2004. 

[10]Gunderson, J. P. and Gunderson, L. F. “Mom! The 

Vacuum Cleaner is Chasing the Dog Again,” Proceedings of 

the 2003 PerMIS Workshop. 2003. 

[11]Yoerg, S. I., Clever as a Fox, New York: Bloomsbury, 

2001, ch. 8, pp. 162-175 

[12]Milton, K. “Distribution Patterns of Tropical Plant 

Food as a Stimulus tp Primate Mental Development,” 

American Anthropologist, vol. 83, pp. 534-548. 

[13]Barbour, M.G., Burk, J.H., and Pitts, W.D. Terrestrial 

Plant Ecology, Menlo Park: CA, 1987, ch.3, pp.29-30. 

[14]Gunderson, J.P. and Martin, W. N. “A ProbailityAware Planning Architecture to Support Variable 

Autonomy,” American Association for Artificail 

Intelligence Technical Report SS-03-04, Menlo Park, CA: 

AAAI Press, pp. 83 – 88. 
Intelligence? 

Ron Cottam, Willy Ranson and Roger Vounckx 

In a very specific way, intelligence and 

information-processing are synonymous. 

Information-processing takes place 

between differently-scaled models of a 

relevant context. The way in which these 

models relate to each other, and therefore the 

result of an inter-scalar processing, depends 

on the constraints which are imposed on interscalar computation, and on the manner in 

which those constraints are applied. 

Mono-scalar ‘systems’ can always be 

deconstructed more or less precisely to a set of 

rules: a single non-fragmented scale 

corresponds to a single formalization. Any 

consequent ‘systemic’ complexity is the result 

of formal incompleteness or of our lack of 

understanding. 

Multi-scalar ‘systems’ constitute 

artificially- or naturally-constrained 

hierarchies, where the style of processing 

depends on whether the inter-scalar 

constraints are externally imposed or 

internally recursively generated by the 

information-processing itself. These two types 

of hierarchy, artificial and natural, have very 

different properties, and exhibit completely 

different styles of ‘intelligence’. 

The unification of a processing 

assembly into a ‘system’ is always through 

our intervention, whether at a single scale or 

across multiple scales of operation. If an 

artificial hierarchy is not to be scalefragmented, it must possess some kind of 

cross-scalar coherence, imposed through our 

manipulation of the inter-scalar constraints. A 

natural hierarchy generates this cross-scalar 

coherence itself, through an autonomynegotiation between its various scales, 

creating a hyperscalar system. 

This appears to be the ‘meaning’ of 

intelligence: it enables a multi-scalar system to 

operate as if it were simultaneously multiscalar and mono-scalar. Different individual 

scales of operation retain a context-dependent 

degree of autonomy, but the entire assembly is 

unified at a hyperscalar level. 

A ‘system’ is always hyperscalar, 

whether through artificially- or naturallyimposed constraints. It is questionable whether 

it would be possible to generate sufficient 

cross-scalar correlation in an artificial 

information-processing assembly to generate 

an interesting or useful degree of independent 

‘intelligence’. In any case, any attempt to do 

so in a definably-operating assembly such as a 

Boolean logic computer could only succeed if 

the logical definability were relaxed, either by 

intention or through the relativistic isolation of 

different parts of the assembly. Even then, 

current artificial information-processing 

mechanisms would be incapable of dealing 

non-catastrophically with the unpredictable 

structural incompletenesses. 
Application of a Crash Prevention Boundary Metric to a 

Road Departure Warning System

S. Szabo 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

B. Wilson 

Volpe National Transportation Systems Center 

Cambridge, MA 02142 

ABSTRACT1

 The U.S. Department of Transportation is actively 

involved in assessing the benefit of road departure 

warning systems (RDWS). A crash prevention 

boundary (CPB) metric has been proposed as one 

means of objectively measuring system performance. 

This paper presents the results of applying the CPB 

metric to data collected during the validation of an 

experimental RDWS. Two types of road departure 

warning scenarios are examined: curve speed and 

lateral departure. 

KEYWORDS: road departure, crash warning 

system, metrics, crash prevention boundary 

1 INTRODUCTION 

The U.S. Department of Transportation is 

actively involved in assessing the benefit of road 

departure warning systems (RDWS) that may 

help reduce the number of collisions and deaths. 

Many types of metrics designed to objectively 

quantify warning system performance are being 

considered. The crash prevention boundary 

(CPB) metric can be used to determine the 

amount of acceleration required to avoid a crash 

as a function of the timing or location of a 

warning [1][2]. A series of tests consisting of 

potential crash scenarios designed to elicit a 

warning [3] were conducted using an 

experimental RDWS. Data was collected during 

the test using an independent measurement 

system. The data was analyzed using the CPB 

 

1 No approval or endorsement of any 

commercial product by the National Institute of 

Standards and Technology is intended or 

implied. This publication was prepared by of the 

United States Government employees as part of 

their official duties and is not subject to 

copyright. 

metric, with a focus on evaluating the timeliness 

of the warning. The warning system provided a 

warning in almost all cases, but a determination 

of whether the warning was late or early relied 

upon a pass/fail criterion established by the 

warning system's designers. The government is 

interested in establishing a baseline of acceptable 

system performance, which is intended to help 

convince the driving public that these systems 

provide a worthwhile benefit. The CPB metric 

may prove useful in establishing a performance 

baseline. This paper shows how the CPB metric 

can be used to analyze two types of road 

departure warning scenarios: curve speed and 

lateral departure. For this particular warning 

system, the results of the CPB analyses indicate 

that the deceleration required to negotiate a curve 

safely has a markedly different profile than the 

lateral acceleration required to avoid running off 

the road. 

A measurement system for analyzing 

warning system performance is also described. 

The paper closes with some recommendations 

for future warning-algorithm metrics and design 

guidelines. 

2 MEASUREMENT SYSTEM 

An independent measurement system (IMS) was 

developed by National Institute of Standards and 

Technology (NIST) for evaluating warning 

system performance. The IMS allows evaluators 

to measure performance without relying on the 

system under test for sensor data. In addition, 

the IMS provides redundancy, quality control 

and an opportunity to collect miscellaneous data 

for additional analysis (e.g., data for validating 

the CPB metric was collected using the IMS). 

The IMS consists of three video cameras 

mounted on a detachable roof rack (Figure 1) 

and a fourth camera pointed at the warning 

system’s dash display. A microphone is located 

in the cab to capture the audible warnings issued 
by the system and to capture comments from the 

driver. The videos from the four cameras are fed 

into a multiplexer producing the image shown in 

Figure 2. The output of the multiplexer is 

recorded onto a digital video recorder (DVR). A 

GPS antenna is mounted on the roof and the raw 

output of the GPS receiver is recorded on the 

second audio channel of the DVR at a one Hz 

rate, ensuring that the GPS data is synchronized 

with the output from all four cameras. The GPS 

data is post-processed using National Geodetic 

Survey Continuously Operating Reference 

Stations (http://www.ngs.noaa.gov/CORS). The 

side and forward cameras are calibrated so that 

pixel coordinates can be transformed into ground 

coordinates either in a GPS-referenced 

coordinate system or in a local-vehicle 

coordinate system. Analysis software is used to 

view video and the vehicle’s trajectory, for 

making measurements to lane markers and 

obstacles, and for calculating a curve’s location 

and radius. 

Figure 1. Three weatherproof cameras mounted 

on roof rack. 

Figure 2. Images from roof-mounted cameras 

and dash-view camera are multiplexed into a 

single quad image. The dash-view camera 

shows an active imminent warning icon.

3 CURVE SPEED CRASH 

PREVENTION BOUNDARY 

Curve speed tests consist of a vehicle traveling 

straight toward a curve at an excessive speed. 

Figure 3 shows the geometry used for the CPB 

analysis. The curve shows a critical point (CP) a 

short distance into the curve. The warning is 

given at a distance of x (meters) prior to the CP. 

xw

Critical

Point (CP)

Vehicle

path

Curve

r

Figure 3 Geometry of curve speed test

Drivers who receive a legitimate warning (a 

true positive) have a range of reaction times and 

decelerations levels available to them sufficient 

to avoid a collision. The locus of the required 

deceleration versus the reaction time is known as 

the CPB. The following equation provides the 

CPB for the curve speed-warning situation 

depicted in Figure 3. This version of the CPB 

equation relates warning location to the required 

longitudinal deceleration for negotiating the 

approaching curve using the following equation: 

( ) w r o

o s

req x t v

v v d −− = 2

2 2 (1) 

Where: 

v0 = vehicle initial forward speed 

vs = safe speed for the curve 

tr = driver reaction time 

xw = the distance between the warning 

location and the CP 

dreq = the deceleration required to reach the 

safe speed at the CP 

Although details of the RDWS warning 

algorithm are proprietary, a public algorithm 

under development by the Applied Physics 

Laboratory and NHTSA [4] provides insight into 

the general warning process. The algorithm 

assumes a warning system has different 

sensitivity settings that will affect the location of 

a warning. The settings use values for the 
desired limit of lateral acceleration (As) in a 

curve and longitudinal deceleration before the 

curve (DW). The lateral acceleration limit is 

used to determine the safe speed going into the 

curve as follows: 

v A r s = s

(2) 

The values for each setting used in this 

analysis are given in Table 1. A near setting 

means that the driver would like a warning closer 

to the curve’s entry, which means that the driver 

is comfortable applying a greater deceleration 

before the curve and carrying a higher lateral 

acceleration through the curve. One can think of 

these values as defining a typical driver’s 

projected velocity profile for the curve-warning 

algorithm. The first phase of the profile has a 

constant velocity equal to v0. The warning 

occurs and the velocity is maintained for 1.5 s. 

Afterwards, the velocity ramps down based on 

Dw until vs is reached. 

 Sensitivity Setting As Dw

1 Near 0.42 g 0.70 g 

2 Near-mid 0.36 g 0.60 g 

3 Mid 0.30 g 0.50 g 

4 Mid-far 0.24 g 0.40 g 

5 Far 0.18 g 0.30 g 

Table 1 Sensitivity settings for APL/NHTSA 

CSW public algorithm.

The curve speed test was conducted on the 

Transportation Research Center (TRC) winding 

road course (Figure 4) on October 2, 2003. The 

vehicle starts at point E, reaches a speed of 50 

mph (22 m/s) by point D and travels through 

curve C. The vehicle should provide a warning 

before reaching curve C. The radius of curve C, 

measured using the IMS, is 115.7 m ± 0.5 m. 

The vehicle speed during each test, measured 

using the GPS, was 48.8 mph ± 0.05 mph (21.8 

m/s ± 0.02 m/s). The lateral acceleration (v

2

/r) in 

the curve if the speed is maintained is 0.42 g. 

Figure 4. TRC winding road course. 

Analysis was performed on data collected 

from test runs where vehicle travels from E 

into curve C.

The experimental warning system produces 

two levels of warning: cautionary and imminent. 

As a driver approaches the curve at an excessive 

speed, the system will first issue a cautionary 

warning. If the driver fails to reduce the 

vehicle’s speed, the system will then issue an 

imminent warning. Figure 5 shows test results 

for cautionary warnings and Figure 6 shows test 

results for imminent warnings. Each crash 

prevention boundary curve in the figures is 

plotted using equation (1), with the mid-level 

sensitivity setting used to determine the safe 

speed and xw set to the location of the warning 

for a given run. Based on the location of the 

warning, the curves describe the required 

longitudinal deceleration to reach the safe speed 

for a given driver reaction time. 

The plots should not be interpreted as 

classical CPBs. In a classical CPB, a driver 

reacting to a warning must decelerate at a level 

above the level shown in the curve that 

corresponds to the specific lapse between the 

warning and the driver’s response. For example, 

CPBs for slower and stopped lead vehicles [5] 

specify the required decelerations for cases in 

which a following vehicle is approaching a lead 

vehicle and receives a rear-end collision 

warning. Drivers decelerating at lower levels 

than those provided by the curves will crash. In 

the longitudinal CPBs in Figure 5 and Figure 6, 

in contrast, drivers that take longer to react and 

decelerate less will not necessarily crash. 

Rather, they will need to negotiate the curve, at 
least initially, faster than the safe speed in 

equation (2). Section 5 will comment on this. 

Figure 5. Longitudinal CPB for series of 

cautionary warnings. Each curve corresponds to 

the location of a warning during test runs.

Figure 6. Longitudinal CPB for series of 

imminent warnings

4 ROAD DEPARTURE CRASH 

PREVENTION BOUNDARY 

Lateral drift tests consist of a vehicle traveling at 

a constant speed and departing the road at a 

constant angle. Figure 7 shows the geometry for 

a lateral drift into a jersey barrier. The location 

of a warning, yw, is the distance from the vehicle 

to the road edge (or other boundary) at the time 

of warning. A warning should provide the driver 

time to react and steer away from the road 

boundary. 

θ

yw

Lane

Marker

Jersey

Barrier

Figure 7. Geometry of a lateral drift test. In this 

test, the Jersey barrier is the road boundary.

Reference [2] also provides a CPB equation 

that can be used to relate warning location to the 

required lateral acceleration to avoid a lateral 

departure using the following equation: 

( )

( ) θ

θ

y t v

v

a

w r

lat − = 2

2

(3) 

Where: 

 v = vehicle forward speed 

θ = departure angle 

alat = lateral acceleration used to avoid 

departure 

tr = driver reaction time 

yw = the distance between the warning 

location and the road boundary 

The validation tests for the warning system 

examined for this paper specify a lateral velocity 

during a departure as opposed to a departure 

angle. The following equation is used to relate 

lateral velocities measured during a test to 

departure angle required in equation (3) (this 

relationship is based on the tangent of the θ, 

which for small angles is equivalent to θ): 

long

lat

v

v θ = (4) 

Where: 

vlat = lateral velocity 

vlong = longitudinal velocity (i.e., forward 

speed or just v) 
Figure 8. Test set-up for road departure toward 

jersey barrier.

One type of test used to analyze the warning 

system is the continuous obstacle test, which 

consists of a straight lateral departure onto a 

shoulder with a jersey barrier offset 1 meter from 

the inside edge of the lane boundary. Tests were 

conducted at the TRC skid pad using a waterfilled jersey barrier (Figure 8.). Cruise control 

was used to set the forward speed during the test 

at 40 mph (18 m/s). The specified lateral 

velocity for the test (i.e., the velocity toward the 

barrier) is 0.4 m/s ± 0.1 m/s. The velocities 

measured using the IMS ranged from 0.3 m/s to 

0.53 m/s. 

Figure 9. Lateral CPB for series of imminent 

warnings 

Figure 9 shows the test results plotted using 

the CPB metric. Note that in this case the curves 

are legitimate CPBs: a driver who receives a 

warning, steers at some tr second(s) later, and 

does not steer with a lateral acceleration greater 

than that corresponding to the value at this tr in 

the appropriate plot will crash. 

5 Future Metrics and Design 

Guidelines 

Having developed longitudinal and lateral CPBs 

in sections 3 and 4, we will now comment on 

them and their utility as a metric. As indicated, 

the longitudinal CPB in section 3 is not a true 

crash prevention boundary, because a driver who 

brakes above the boundary will not necessarily 

crash. Rather, the driver will be forced to 

negotiate a curve’s critical point at a speed 

greater than a predetermined safe speed. A 

driver’s skill level and the available traction will 

determine if a collision occurs. 

Despite this limitation, the longitudinal CPB 

remains a useful metric for both RDWS 

developers and analysts. A developer can readily 

understand the implications of a more aggressive 

warning algorithm, e.g., shown in Figure 6 

versus Figure 5. We see in Figure 5, whose 

CPBs originate from a mid-level (cautionary) 

warning setting, that approximately 0.1 g of 

deceleration is required to negotiate the curve 

safely when the warning is issued. If a driver 

requires 1.5 second to respond, a deceleration of 

approximately 0.15 g is required. 

In Figure 6, we see that a more aggressive 

warning algorithm assumes drivers will react 

more quickly and decelerate at higher levels. 

Indeed, the change in the CPBs between the 

cautionary and imminent CPBs in Figure 5 and 

Figure 6 indicates that in the latter case drivers 

must react in approximately half the time and 

decelerate at approximately twice the level as in 

the former case. 

The lateral CPBs shown in Figure 9 all show 

quite low initial values for the lateral

acceleration that is required to avoid a roaddeparture collision (colliding with the barrier). 

Even 1.5 second later, the required acceleration 

is still quite low. At reaction times greater than 2 

seconds, however, the required acceleration 

increases markedly. 

The different kinematics between curve 

speed warnings and lateral departure warnings 

merit comment. We see in equation (1) that the 

square of vehicle forward speed minus the square 

of the safe speed composes the numerator of the 

term that determines the required deceleration. In 

SI units, 50 mph equals 22.5 m/s and its square is 

506. A safe speed of 35 mph results in a 

numerator of 258, a significant number. The 

lateral CPB counterpart, equation (3), has the 

lateral speed as its sole term in the numerator. A 

lateral speed, even in a departure situation, of 1 

m/s is rare, so the numerator of equation (3) 
typically equals unity or less. Only when the 

actual reaction time starts approaching the 

reaction time programmed into the warning 

algorithm will the denominator of (3) approach 0 

and the required lateral acceleration increase 

rapidly. Thus for curve-speed CPBs, Figure 5 

and Figure 6, we see higher initial values and a 

continuous increase in the required deceleration 

with reaction time. The lateral departure CPB in 

Figure 9 shows a lower initial value in the 

required lateral acceleration and a very flat curve 

until the reaction time times the lateral speed 

approaches the alert distance (i.e., until the 

vehicle is near the road edge or barrier). 

Although not technically part of the CPB, 

we can also use the CPB equations to determine 

the sensitivity of the required deceleration or 

lateral acceleration to sensing errors or 

uncertainty. By taking the derivative with respect 

to the warning distance, xw, in equation (1), we 

can determine the sensitivity of the required 

acceleration to uncertainty in the warning 

distance: 

r o

req req nom

x t v

d

dx

d

− = − _ (5) 

where dreq_nom is the nominal required 

deceleration from equation (1). An initial 

warning distance of, say, x = 50 m decreases the 

sensitivity of the required deceleration to errors 

in the warning distance by a factor of 50. The 

effect of these errors, however, becomes more 

pronounced as the reaction distance (initial speed 

times the time required to decelerate) approaches 

the warning distance. 

The sensitivity of the required lateral 

acceleration to errors in the lateral distance has a 

form identical to equation (5): 

y t vθ

a

dy

a

r

req req nom

− = − _ (6) 

In this case both the lateral warning-position 

errors and the warning position (y) will be 

smaller than their longitudinal counterparts, so 

the sensitivity of the required lateral acceleration 

to lateral sensing errors (or uncertainty) is low, at 

least when the warning is issued. As the 

denominator in equation (6) decreases, the 

sensitivity, of course, increases. 

5.1 Lateral Sensing

The lateral CPB curves in Figure 9 are highly 

dependent on the estimated lateral speed and the 

estimated distance from the road edge (or 

barrier). The vertical asymptotes occur when the 

product of the reaction time and lateral speed 

equals the warning distance. Although there are a 

number of sensing issues, we will call attention 

to only one of them: the lateral distance used to 

issue a warning. The CPBs in Figure 9 result 

from using the actual distance between the 

vehicle’s front bumper and the barrier in the 

CPB equation (3). The variation in the CPBs 

results from variations in the initial conditions as 

well as variations in the lateral-distance 

estimates. We believe, however, that a 

reasonable range of initial conditions should not 

produce variations in CPBs. Drivers should be 

warned consistently, with the understanding: 

“You need to steer out of this with a timing and 

level consistent with how you adjusted the 

sensitivity.” A wide variation in the required 

timing and level, which will result from 

improper sensing or processing, violates this 

understanding and may lead to driver 

dissatisfaction. The CPB is a useful tool for 

showing this variation, or lack thereof, for a 

series of warnings and conditions. 

5.2 Extensions

As indicated in Section 3, the longitudinal CPB 

in this paper is not a true CPB because it merely 

represents the required deceleration to negotiate 

a curve at a predetermined safe speed. Beyond 

this issue, however, lies the larger problem of 

describing a general CPB for negotiating a curve 

safely. In our tests, we observed that after 

receiving the alert the driver decelerated and 

continued decelerating while turning. Other 

efforts (and expected behavior) demonstrate this 

same trend: drivers brake before the curve and 

continue to brake while negotiating curves, at 

least at the curve entrance. In addition, drivers 

often “cut” the curve, further complicating 

efforts to model vehicle motion and crash 

boundaries. Given that (1) the longitudinal CPB 

in Section 3 is not a true crash prevention 

boundary, (2) drivers may exceed the safe speed 

when entering a curve without necessarily losing 

control, and (3) drivers cut curves, we see some 

limitations in applying the existing analyses to 

describing the CPB of a given curve speed 

warning. The limitation suggests the need for a 

more comprehensive CPB, an effort we are 

pursuing. 
6 References 

[1] Burgett, A., Gunderson, K., “Crash 

Prevention Boundary for Road Departure 

Crashes-Derivation”, DOT HS 809 399, 

September 2001. 

[2] Wilson, B., Burgett, A, “Crash Prevention 

Boundaries for Road Departure”, Ninth 

World Congress on Intelligent 

Transportation Systems, Chicago, 

IL.October, 2002. 

[3] Szabo, S. Norcross, R., “Recommendations 

for Objective Test Procedures for Road 

Departure Crash Warning Systems”, NIST 

report under Agreement Number DTFH61-

00-Y-30132, February 18, 2003. 

[4] Deal, F.C., Men, H., Phamdo, N., “Single 

Vehicle Roadway Departure Prevention 

Program – Public Curve Speed Warning 

(CSW) and Lateral Drift Warning (LDW) 

Algorithms Design and Performance”, Draft 

report prepared by Johns Hopkins Applied 

Physics Laboratory, April 2004. 

[5] Wilson, B., “How Soon To Brake and How 

Hard To Brake: Unified Analysis of the 

Envelope of Opportunity for Rear-End 

Collision Warning Systems,” 17th 

International Technical Conference on the 

Enhanced Safety of Vehicles, Amsterdam. 

June, 2001 
PRIDE: A Framework for Performance Evaluation of 

Intelligent Vehicles in Dynamic, On-Road Environments 

Craig Schlenoff, Jerome Ajot, and Raj Madhavan 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

ABSTRACT 

We are developing a novel framework, PRIDE (PRediction In 

Dynamic Environments), to perform moving object prediction for 

unmanned ground vehicles. The underlying concept is based upon 

a multi-resolutional, hierarchical approach that incorporates 

multiple prediction algorithms into a single, unifying framework. 

The lower levels of the framework utilize estimation-theoretic 

short-term predictions while the upper levels utilize a probabilistic 

prediction approach based on situation recognition with an 

underlying cost model. 

 In addition to predicting the location of moving objects in the 

environment, we have extended PRIDE to generate simulated 

traffic flow during on-road driving. In this paper, we explore 

applying the PRIDE-based traffic control algorithms for the 

purpose of performance evaluation of autonomous vehicles. 

Through the use of repeatable and realistic traffic flow simulation, 

one is able to evaluate the performance of an autonomous vehicle 

in an on-road driving scenario without the risk involved with 

introducing the vehicle into a potentially dangerous roadway 

situation. In addition, by varying a single vehicle’s parameters 

(e.g. aggressivity, speed, location) with the traffic flow, we can 

show how the entire traffic pattern is affected. We will show the 

successes that have been achieved to date in a simulated 

environment, as well as enhancements that are currently being 

researched and expected in the near future. 

KEYWORDS: autonomous vehicle, on-road driving, traffic 

simulation, performance metrics, PRIDE

1.0 Introduction/Problem Statement 

The field of autonomous systems is continuing to gain 

traction both with researchers and practitioners. Funding for 

research is this area has continued to grow over the past few 

years, and recent high profile funding opportunities have 

started to push theoretical research efforts into practical use. 

Autonomous systems in this context refer to embodied 

intelligent systems that can operate fairly independently 

from human supervision. 

 Many believe that the DEMO III Experimental 

Unmanned Vehicle (XUV) effort represents the state of the 

art in autonomous off-road driving [10]. This effort seeks to 

develop and demonstrate new and evolving autonomous 

vehicle technology, emphasizing perception, navigation, 

intelligent system architecture, and planning. It should be 

noted the DEMO-III XUV has only been tested in static 

environments. It has not been tested in on-road driving 

situations, which include pedestrians and oncoming traffic. 

 There have been experiments performed with 

autonomous vehicles during on-road navigation. Perhaps the 

most successful has been that of Dickmanns [4] as part of 

the European Prometheus project in which the autonomous 

vehicle performed a trip from Munich to Odense (over 

1,600 kilometers) at a maximum velocity of 180 km/hr. 

Although the vehicle was able to identify and track other 

moving vehicles in the environment, it could only make 

basic predictions of where those vehicles were expected to 

be at points in the future, considering the vehicle’s current 

velocity and acceleration. 

 What is missing from all of these experiments is a level 

of situation awareness of how other vehicles in the 

environment are expected to behave considering the 

situation in which they find themselves. When humans 

drive, we often have expectations of how each object in the 

environment is expected to move based upon the situation. 

When a vehicle is approaching an object that is stopped in 

the road, we expect it to slow down behind the object or try 

to pass it. When we see a vehicle with its blinker on, we 

expect it to turn or change lanes. When we see a vehicle 

traveling behind another vehicle at a constant speed, we 

expect it to continue traveling at that speed. The decisions 

that we make in our vehicle are largely a function of the 

assumptions we make about the behavior of other vehicles. 

 To date, the authors are not aware of any autonomous 

vehicle efforts that account for this information when 

performing path planning. To address this need, we have 

developed a framework, called PRIDE (PRediction in 

Dynamic Environments) that provides an autonomous 

vehicle’s planning system with information that it needs to 

perform path planning in the presence of moving objects 

[8]. In this paper, we describe how we leveraged the 

algorithms in the PRIDE framework to simulate traffic 

patterns during on-road driving. We can then use these 

simulated traffic patterns to control vehicles in the 

environment in an on-road driving arena being developed at 

NIST [9] in a way to assess the performance of autonomous 

vehicles being tested within these arenas. 

 In Section 2, we survey some related work in traffic 

simulation. In Section 3, we describe the various 

components of the PRIDE framework. In Section 4, we 

show how the PRIDE framework can be applied to traffic 

simulation for on-road driving. In Section 5, we explain 

how this traffic simulation can be used to apply 
performance metrics for autonomous vehicles. Section 6 

concludes the paper. 

2. RELATED WORK 

Most of the work in the literature dealing with drivers’ 

actions and predicted behavior has been performed by 

psychologists in an attempt to explain drivers' behaviors and 

to identify the reasons of certain dysfunctions. 

There have been a few efforts that have tried to simulate 

traffic patterns. One of more prominent ones in the literature 

is ARCHISM [3,5], but even this effort is based upon 

driving psychology studies. These traffic simulations use 

laws that can be applied for a specific environment or a 

specific situation. Some of those postulates can be expand 

to generic situations but still attached to a kind of situation. 

3. THE PRIDE FRAMEWORK 

We are using the 4D/RCS (Real-Time Control System) 

reference model architecture [1] as the basis in which to 

apply the representational approaches that are being 

developed in this effort. 4D/RCS was chosen due to its 

explicit and well-defined world modeling capabilities and 

interfaces, as well as its multi-resolution, hierarchical 

planning approach. Specifically, 4D/RCS allows for 

planning at multiple levels of abstraction, using different 

planning approaches as well as utilizing inherently different 

world model representation requirements. By applying this 

architecture, we can ensure that the representations being 

developed for representing moving objects can 

accommodate different types of planners that have different 

representational requirements. 

 The RCS architecture supports multiple behavior 

generation (BG) systems working cooperatively to compute 

a final plan for the autonomous system. The spatial and 

temporal resolution of the individual BG systems along with 

the amount of time allowed for each BG system to compute 

a solution are specified by the level of the architecture 

where it resides. In addition to multiple BG systems, 

multiple world models are supported with each world 

model’s content being tailored to the systems that it 

supports (in this case the BG system). As such, it is 

necessary for moving objects to be represented differently at 

the different levels of the architecture. 

 To support this requirement, NIST has developed the 

PRIDE (PRediction In Dynamic Environments) framework. 

The underlying concept is based upon a multi-resolutional, 

hierarchical approach that incorporates multiple prediction 

algorithms into a single, unifying framework. This 

framework supports the prediction of the future location of 

moving objects at various levels of resolution, thus 

providing prediction information at the frequency and level 

of abstraction necessary for planners at different levels 

within the hierarchy. To date, two prediction approaches 

have been applied to this framework. 

 At the lowers levels, we utilize estimation theoretic 

short-term predictions via an extended Kalman filter-based 

algorithm using sensor data to predict the future location of 

moving objects with an associated confidence measure. 

Estimation-theoretic schemes using Kalman Filters (KFs) 

are well established recursive state estimation techniques 

where estimates the states of a system are computed using 

the process and observation models [6]. The recursive 

nature of the algorithm utilizes the system's CPU more 

uniformly to provide estimates without the latency resulting 

from batch processing techniques. The (linear) KF is simply 

a recursive estimation algorithm that provides minimum 

mean squared estimates (MMSE) of the states of a linear 

system utilizing knowledge about the process and 

measurement dynamics, process and measurement noise 

statistics subject to Gaussian assumptions and initial 

condition information. When these assumptions are 

satisfied, the estimates provided by the Kalman filter are 

optimal. The extension of the linear Kalman filtering ideas 

to a non-linear system is termed extended Kalman filtering. 

 The Extended Kalman Filter (EKF) is a linear estimator 

for a non-linear system obtained by linearization of the 

nonlinear state and observation equations. For any nonlinear system, the EKF is the best linear unbiased estimator 

with respect to minimum mean squared error criteria. 

Within the on-road driving hierarchy, short-term prediction 

of objects moving at variable speeds and at given lookahead time instants are predicted using the EKF. More 

information about this approach can be found in [7]. 

 At the higher levels of the framework, moving object 

prediction needs to occur at a much lower frequency and a 

greater level of inaccuracy is tolerable. At these levels, 

moving objects are identified as far as the sensors can 

detect, and a determination is made as to which objects 

should be classified as “objects of interest”. In this context, 

an object of interest is an object that has a possibility of 

affecting our path in the time horizon in which we are 

planning. At this level, we use a moving object prediction 

approach based on situation recognition and probabilistic 

prediction algorithms to predict where we expect that object 

to be at various time steps into the future. Situation 

recognition is performed using spatio-temporal reasoning 

and pattern matching with an a priori database of situations 

that are expected to be seen in the environment. In these 

algorithms, we are typically looking at planning horizons on 

the order of tens of seconds into the future with plan steps at 

about one second intervals. At this level, we are not looking 

to predict the exact location of the moving object. Instead, 

we are attempting to characterize the types of actions we 

expect the moving object to take and the approximate 

location the moving object would be in if it took that action. 

More information about this approach is included in the 

follow section. 
Active research is exploring the integration of these two

prediction approaches in a way that the predictions from one

can help to enforce or not enforce the predictions of the 

other. 

Both of these prediction methods have been

implemented in two different simulation environments. The

EKF approach has been implemented in the OneSaf testbed 

(www.onesaf.com). OneSaf is a composable, next

generation computer generated forces (CGF) that represents

a full range of operations, systems, and control process from

individual combatant and platform to battalion level, with a 

variable level of fidelity. OneSaf is able to represent moving

objects and provide the object's location and velocity at any

point in time, through custom-developed Application

Programmers’ Interface (API) calls. A user-interface was 

built on top of OneSaf to display the predicted locations of 

the moving objects. 

In Figure 1, the triangle represents the moving object

whose future location is to be predicted. The large circle in

front of the triangle is the area in which we are 99 % 

confident that the object will be in two seconds and the 

small shaded circle is the area in which we are 50 % 

confident that the object will be in two seconds. For our 

implementation, we found that the EKF provided reasonable

predictions within a two second horizon. A horizon greater

than two seconds introduced too much uncertainty to be

useful for our autonomous driving scenarios.

The situation-based probabilistic prediction approach 

has been implemented in the AutoSim simulation package 

developed by Advanced Technology Research Corporationi

. 

AutoSim is a high-fidelity simulation tool which models 

details about road networks, including individual lanes, lane

markings, intersections, legal intersection traversibility, etc. 

Using this package, we have simulated typical traffic 

situations (e.g., multiple cars negotiating around obstacles 

in the roadway, bi-directional opposing traffic, etc.) and 

have predicted the future location of individual vehicles on

the roadway based upon the prediction of where other 

vehicles are expected to be. 

At the point this paper was written, we have simulated

a handful of driving situations and have used approximately

a dozen costs to determine the probabilities of one action 

over another. In this context, a cost is a penalty that is

incurred by performing a maneuver or occupying a state. 

Current costs are incurred based on: 1) proximity to other

objects in the environment as a function of necessary 

stopping distance, 2) exceeding or going below the speed

limit by a given threshold, 3) changing lanes, 4) not being in

the rightmost lane, 5) rapidly accelerating or decelerating, 

and 6) changing lanes where double yellow lines in the road

exist, among other costs.

It should be emphasized that costs are not static

numbers. The cost that a vehicle incurs by taking an action 

is heavily a function of the perceived personality and

intention of the moving objects. Using these costs, we are 

able to predict up to ten seconds into the future at a rate of 

two predictions per second. A snapshot of the

implementation is shown in Figure 2 (a) and (b). 

4. APPLYING THE PRIDE FRAMEWORK 

TO TRAFFIC SIMULATION 

Although the PRIDE framework was originally developed 

to inform a planner about the future position of moving

Figure 2: Situation-based probablistic prediction. (a) above and (b)

below show a vehicle performing a passing operation around stationary

obstacles. 

Figure 1: Short-term Prediction.
objects for the purpose of path planning and collision 

avoidance, we have found that the same set of algorithms

could be applied to simulating traffic patterns during onroad driving. More specifically, we applied the situation 

recognition and probabilistic algorithms to determine the 

likely actions that a vehicle in the environment would take

when confronted with a specific situation, and then

command that vehicle to perform that action. By doing this

with multiple vehicles, we are able to simulate fairly

sophisticated traffic situations in which vehicles behave in a

way that is very similar to how a human would behave.

Vehicles will slow down and/or pass when approaching a 

stopped or slow object in their lane, they will typically only 

change lanes when the next lane is clear and they are going 

slower than desired, they will keep a safe follow distance, 

etc. By providing realistic simulations of traffic situations, 

we are able to test the autonomous vehicle during realistic 

on-road driving situations, without having to place the 

vehicle on a potentially dangerous city street or highway.

Figure 3: Discretized Vehicle’s Actions.

As shown, at any point in time, the vehicle can have up to

15 possible future actions. 

4.2. THE PRIDE ALGORITHMS 

In this section, we will use the following scenario as 

shown in Figure 4 to explain the concepts in the algorithms. 

This scenario is composed by three vehicles, two (A and B)

on the same lane (L1) and another one (C) on the opposite

lane (L2) and a static obstacle (D) on the lane L1. The vision is that we will use these algorithms

originally in simulated environments (such as the OneSaf 

and AutoSim simulation environments discussed above) to

test out the planning algorithms in the presence of moving

objects. Then, when the NIST On-Road Driving Arenas

(which are described in another paper in this conference),

are completed, these algorithms will be used to control

“environmental” vehicles in the arena to simulate on-road 

traffic. 

Figure 4: Scenario

Figure 5 shows the overall process for the algorithms (a) 

graphically and (b) in pseudo-code. The algorithm proceeds 

as follows: 

The remainder of this section describes the details of

how the situation recognition and probabilistic algorithms

are used to simulate on-road traffic. 1. For each vehicle on the road (α), the algorithm gets 

the current position and velocity from external 

programs/sensors (β).

The basic assumption behind this situation-based 

probabilistic prediction approach is a driver’s behavior can 

be quantified using costs. In general, a driver will prefer an 

action that minimizes its cost. With this assumption, the cost 

can be converted to probabilities, where the higher the cost,

the lower the probability that the driver will execute that 

action. 

2. For each time in the future and for each starting 

position (χ), the algorithm creates a set of next 

possible positions in the future and assigns a cost

to each of them corresponding to the action 

performed and the state occupied. At the end of the

first prediction, each ending position is set at the

starting positions at time t are used as “starting 

position” to build the next set of future position for

time t+1. This loop (δ) is performed tfinal iterations,

where tfinal is the predetermined time in the future 

that we wish to predict. 

4.1. POSSIBLE VEHICLE ACTIONS 

For the purpose of the algorithms, we have discretized the 

possible actions that a vehicle can make at any given time.

Note that for this exercise, we have not accounted for 

intersections. All of the examples occur on a continuous 

stretch of roadway. 3. Using the costs found in step 2, the algorithm 

computes the probability for each movements of

the vehicle (ε). In Figure 6, ten possible positions

are shown for the vehicle (a) A, (b) B, and (c) C at 

time tfinal. 

A vehicle can execute two types of actions. The first

type of action is regarding its velocity, namely, quick 

acceleration (QA), slow acceleration (SA), constant velocity 

(CV), slow deceleration (SD) and quick deceleration (QD). 4. The width of each dot in Figure 6 represents the

relative probability of each action with respect to 

the others, where the bigger the dot, the higher the 

probability. 

The second type of action is regarding lane changing, 

namely, changing to the left lane (CL), staying in the same

lane (SL) and changing to the right lane (CR). These are 

shown in Figure 3. 
Begin 

 Loop 

 For each vehicle (α) 

 Get Current Position (β) 

 For each time in the future (χ) 

 For each possible actions (δ) 

 Compute All Moves 

 Calculate Cost Action 

 Calculate Cost Static Obstacle 

 End for 

 Calculate Probabilities Action (ε) 

 End for 

 Build Predicted Vehicle Trajectory (ξ) 

 End for 

 For each Predicted Vehicle Trajectory (η) 

 If Probable Vehicle Collision 

 Then Calculate Cost Collision 

 End if 

 End for 

 Calculate Final Probabilities (θ) 

 End Loop 

End. 

Figure 5 (a) (above) schematic of overall process, (b) (below) pseudo code

5. The algorithm then builds the Predicted Vehicle 

Trajectories (ξ) which will be used to evaluate the 

possibly of colliding with another vehicle. The 

Predicted Vehicle Trajectory notion is explained

later in this document. 

6. For each pair of Predicted Vehicle Trajectory (η), 

the algorithm checks if there is a probable collision

and assigns a cost to the collision.

7. In the example, for the vehicles A and C, Figure 7 

shows that one possible trajectory for A intersects a 

possible trajectory for C, thus resulting in a 

collision.

Figure 6: Predicted Positions of (a) (top) Vehicle A, (b) (middle) Vehicle B, 

and (c) (bottom) Vehicle C.

8. The probabilities (θ) based on the costs of each 

action are recalculated based upon the collision

information. Figure 8 shows the final vehicle

probabilities for Vehicles A, B, and C. Notice how 

the size of the dots have changed from Figure 5,

thus accounting for the cost due to possible 

collisions. 

Figure 7: Possible Collision Between A and C 

At the end of the main loop, the path with the highest

probability for each vehicle represents the most likely 

location where the vehicles will be in tfinal in the future. 

Figure 8: Final Vehicle Probabilities for (a) Vehicle A, (b) Vehicle B, and 

(c) Vehicle C. 

4.3. COST MODEL AND PROBABILITY 

The moving object prediction (MOP) algorithms can be 

separated in two parts, the first one is the creation of a set a 

predicted positions for each vehicle and the second is the 

evaluation of the interaction between each vehicle on the 

road. Every evaluation is based on costs that are converted

to probabilities. 

The Cost Model (CM) assigns danger ratings (cost) to

each action that a vehicle can perform and the states that it 
x1 t 1 xPP1t 1 xIP1 1 t 1

y1 t 1 yPP1t 1 yIP1 1 t

1

where t 1 0,1 occupies after performing that action. This exact cost

assigned to each action and state depends upon the 

aggressivity of the driver. 

The cost of an action is the sum of the costs that are

encountered by performing that action, which could include 

a cost for changing lanes, a cost for accelerating, a cost for 

going over the speed limit, etc. The cost of the state is 

described in the next section. This approach for building

costs is based upon work performed in [2].

x2 t2 xPP2t 2 xIP2 1 t2

y2 t

2 yPP2t 2 yIP2 1 t 2

where t 2 0,1

where t1 and t2 are the parameters of each PVT. 

By using the Theorem of Cramer, t1 and t2 can be

determined: 

4.4. PREDICTED VEHICLE TRAJECTORY 

The Predicted Vehicle Trajectory (PVT) represents the

possible movements of a vehicle throughout the time period

being analyzed. The PVT is a representation of the

trajectory, as shown in Figure 9.

xPP1 t1 xIP1 1 t 1 xPP2t 2 xIP2 1 t2

yPP1t 1 yIP1 1 t 1 yPP2 t 2 yIP2 1 t 2

xPP1 xIP1 t 1 xIP2 xPP2 t 2 xIP2 xIP1

yPP1 yIP1 t1 yIP2 yPP2 t 2 yIP2 yIP1

Figure 9: Predicted Vehicle Trajectory. 

t 1

xIP2 xIP1 xIP2 xPP2

yIP2 yIP1 yIP2 yPP2

xPP1 xIP1 xIP2 xPP2

yPP1 yIP1 yIP2 yPP2

The PVT is built with the origin position {xIP, yIP, tIP = 0} at

time = 0 and the predicted position {xPP, yPP, tPP = tfinal}

where tfinal is the predetermined time in the future for the 

prediction process. It also contains the action-cost and 

action-probability information. 

t 2

xPP1 xIP1 xIP2 xIP1

yPP1 yIP1 yIP2 yIP1

xPP1 xIP1 xIP2 xPP2

yPP1 yIP1 yIP2 yPP2

The PVT is used to determine possible collisions. 

Because the PVT represents a trajectory of one vehicle 

(origin to predicted), we can determine possible collision 

between any two vehicles by determining if two PVTs 

cross. 

Figure 10: Two PVTs Crossing.

So the two vehicles will cross each other at two different 

times t1tfinal for the first vehicle and t2tfinal for the second one. 

For a small difference between the two time, the collision is

highly likely. Conversely, if the difference is large collision 

is improbable. 

The inverse of the difference between the two collision

times represents the coefficient of the collision cost: When two PVTs are crossing each other (Figure 10), it is 

important to know where are they crossing. This

information can be obtained by using a parametrization of

each PVT. CollisionCost M

t final t1 t2

where M is a preset of the Cost Model for collision costs. 

The parametrization:

5. APPLYING TRAFFIC SIMULATION TO 

PERFORMANCE METRICS 
Now that we’ve described how we can simulate traffic 

patterns, we will discuss how this could be used to associate 

performance metrics to an autonomous vehicle. In 

evaluating how an autonomous vehicle is performing during 

on-road driving, we need the ability to test that vehicle in 

various driving situations. Those situations could be a 

function of the environment (e.g., winding roads, steep 

slopes, traffic signals, intersections), weather conditions 

(e.g., rain, fog, ice on the roadway), and static and dynamic 

objects in the environment (e.g., traffic barrels, pedestrians, 

other vehicles). The traffic simulator allows us the ability to 

dynamically change information about static and dynamic 

objects in the environment in order to introduce a variety of 

situations that we can evaluate the autonomous vehicle 

against. 

 The traffic simulator allows one to have repeatable, 

realistic traffic patterns that only vary in response to the 

autonomous vehicle motions. As such, one would be able to 

place two different autonomous vehicles in an identical 

traffic environment to evaluate how each performs. If the 

two autonomous vehicles behaved in identical fashion, the 

entire flow of traffic would be identical. Conversely, if the 

two autonomous vehicles’ behaviors differed in any way, 

the flow of traffic would most likely differ (since other 

vehicles in the traffic pattern may be reacting to the actions 

of the autonomous vehicle). Metrics could be assigned to 

the autonomous vehicle’s actions, based on a number of 

criteria, including proximity to other vehicles, staying 

within the speed limit, number of lane changes, obeying 

traffic signs and signals, etc. 

 The traffic simulator also allows for the ability to vary 

the aggressivity of drivers on the road. Using this capability, 

we could have different difficulties of driving scenarios, 

based, in part, on the aggressivity of the drivers on the road, 

where the higher the aggressivity, the harder the course. 

One could even imagine situations where an accident 

among a pair of traffic vehicles is imminent. The 

autonomous vehicle could then be evaluated based upon its 

ability to predict this accident and take precautions in time. 

6. CONCLUSION 

 

In this paper, we have described the PRIDE framework, 

which was developed to perform moving object prediction 

for unmanned ground vehicles. PRIDE is based upon a 

multi-resolutional, hierarchical approach that incorporates 

multiple prediction algorithms into a single, unifying 

framework. The lower levels of the framework (not 

discussed in detail in the paper) utilize estimation-theoretic 

short-term predictions while the upper levels utilize a 

probabilistic prediction approach based on situation 

recognition with an underlying cost model. We showed the 

results achieved from applying PRIDE in a simulated 

environment.

 We have then shown how PRIDE can be extended to 

simulate traffic patterns during on-road navigation. The 

PRIDE algorithms are used to provide the underlying logic 

to control vehicles in the environment, thus generating a 

realistic flow of traffic. We use the prediction algorithms 

within PRIDE to determine the probability that a vehicle 

will exhibit a certain behavior given a set of environmental 

conditions, and then command the vehicle to perform the 

action which has the greatest probability. By doing this, we 

are able to create realistic, repeatable, and non-scripted 

traffic patterns that closely mimic the types of traffic flow 

expected to be encountered during on-road driving. 

 We then explore how the PRIDE-based traffic control 

algorithms can be applied to performance evaluation of 

autonomous vehicles. Through the use of repeatable and 

realistic traffic flow simulation, one is able to evaluate the 

performance of an autonomous vehicle in an on-road 

driving scenario without the risk involved with introducing 

the vehicle into a potentially dangerous roadway situation. 

In addition, by varying a single vehicle’s parameters (e.g. 

aggressivity, speed, location) with the traffic flow, we can 

show how the entire traffic pattern is affected. 

The goal of this paper was to describe how the work to 

date in moving object prediction could contribute to 

performance metrics for autonomous systems. Though the 

algorithms described in this paper have been developed and 

implemented, there is still much work to be accomplished. 

For one, the metrics that should be applied when evaluating 

an autonomous system in the presence of traffic situations 

being generated by these algorithms need to be determined. 

This will be the topic of future work and will be realized in 

the NIST On-Road Driving Arenas mentioned earlier in the 

paper. Also, these set of algorithms have been shown to 

work successfully on straight roads, but have not been fully 

tested on intersections. This will also be a topic of future 

research.

REFERENCES 

1. Albus, J. and et.al., "4D/RCS Version 2.0: A 

Reference Model Architecture for Unmanned 

Vehicle Systems," NISTIR 6910, National Institute 

of Standards and Technology, Gaithersburg, MD, 

2002. 

 2. Balakirsky, S., A Framework for Planning with 

Incrementally Created Graphs in Attributed Problem 

Spaces, IOS Press, Berlin, 2003. 

 3. Champion, A., Espie, S., and Auberlet, J., 

"Behavioral Road Traffic Simulation with 

ARCHISM," Proceedings of the Summer Computer 

Simulation Conference, USA, 2001. 

 4. Dickmanns, E. D., "An Expectation-Based MultiFocal Saccadic (EMS) Vision System for Vehicle 

Guidance," Proceedings of the 9th International 
Symposium on Robotics Research (ISRR'99), Salt 

Lake City, 1999. 

 5. Espie, S., Saad, F., and Schnetler, B., "Microscopic 

traffic simulation and driver behaviro modeling: the 

ARCHISM project," Proceedings of the Strategic 

Highway Research Program and Traffic Safety on 

Two Continents, Lille, France, 1994. 

 6. Kalman, R., "A New Approach to Linear Filtering 

and Prediction Problems," Transactions of the ASME 

Journal of Basic Engineering, Vol. 82, No. Series D, 

1960, pp. 35-45. 

 7. Madhavan, R. and Schlenoff, C., "The Effect of 

Process Models on Short-term Prediction of Moving 

Objects for Unmanned Ground Vehicles," Submitted 

to the 7th International IEEE Conference on 

Intelligent Transportation Systems, Washington DC, 

2004. 

 8. Schlenoff, C., Madhavan, R., and Barbera, T., "A 

Hierarchical, Multi-Resolutional Moving Object 

Prediction Approach for Autonomous On-Road 

Driving," Proceedings of the 2004 ICRA Conference, 

2004. 

 9. Scrapper, C., Balakirsky, S., and Weiss, B., 

"Autonomous Road Driving Arenas for Perfomance 

Evaluation," To be published in the Proceedings of 

the Perfomance Metrics for Autonomous Systems 

(PerMIS) 2004 workshop, 2004. 

 10. Shoemaker, C. and Bornstein, J. A., "Overview of 

the Demo III UGV Program," Proceedings of the 

SPIE Robotic and Semi-Robotic Ground Vehicle 

Technology Conference, Vol. 3366, 1998, pp. 202-

211. 

 

i

Certain software tools are identified in this paper in order to explain our 

research. Such identification does not imply recommendation or 

endorsement by the National Institute of Standards and Technology, nor 

does it imply that the software tools identified are necessarily the best 

available for the purpose. 
Autonomous Road Driving Arenas for

Performance Evaluation

Chris Scrapper, Stephen Balakirsky, Brian Weiss

National Institute of Standards and Technology

Intelligent Systems Division

Gaithersburg, Maryland 20899

Email: {scrapper, balakirsky, bweiss}@nist.gov

ABSTRACT— The development of performance metrics

is critical in the evaluation and advancement of intelligent systems.

Obtaining the pinnacle of intelligence in autonomous vehicles

requires evolutionary standards and community support. In order

to analyze and compare competing implementations of intelligent

systems, the critical components of the system must be decoupled

to facilitate repeatable trials that target specific aspects of the

system’s overall task. This paper presents a framework for a real

virtual simulation environment that provides the facilities and tools

to formally test the limitations and capabilities of autonomous

road driving vehicles.

Keywords:

Performance Metrics, Autonomous Road Driving,

Real Virtual Simulation, MOAST, RCS

“A major barrier to the development of intelligent

systems is the lack of metrics and quantifiable measures of performance. There cannot be a science of

intelligent systems without standard units of measure.”

[1]

1. Introduction

Autonomous vehicles have made remarkable advancements during the past few decades. Researchers have

produced many systems in the quest to develop intelligent control architectures capable of various autonomy

levels. These advancements have elevated the capabilities

of autonomous driving and have been showcased in many

competitions and events recently. One instance of such

competitions is the Defense Advanced Research Projects

Agency’s (DARPA) Grand Challenge [2], which seeks to

advance a variety of architectures and implementations by

luring researchers to demonstrate their autonomous systems

in a timed, autonomous ground vehicle “race”. However,

a task’s parameters and constraints may dictate that high

speed is not always indicative of successful performance

by an autonomous vehicle (e.g., military operations may

encourage stealth over speed). Thus, autonomous systems

should produce a multitude of behaviors within the same

dynamic environment based upon a particular set of constraints. The success of the architecture relies heavily on

the ability of the intelligent system to be cognizant of its

environment. To accomplish this, intelligent systems must

use perception systems to gather situational information

from non-deterministic, stochastic real world environments.

Following detection and classification of the environment,

the autonomous system selects an appropriate mode of

operation. On-road driving is the mode of operation that

is targeted in this paper.

As the pace of this technology continues to develop and

even accelerates, performance metrics must be designed

and refined to measure the effectiveness of autonomous

systems. An archetypical system will emerge from the

application of these metrics as the eventual pinnacle of autonomous road driving achievement. By this definition, an

autonomous system will have the ability to produce rational

behaviors allowing it to successfully achieve its goals in any

dynamic, unstructured, and complex environment. In order

to realize this archetypical system, critical architecture

components must be de-coupled for independent evaluation.

The evaluation of these components will allow evolutionary

standards to be applied as necessary to help define the

performance metrics, direct the focus of the community,

and encourage collaborative efforts. Without communityacknowledged performance metrics and a complete comprehension of capabilities and limitations, it will be very

difficult to assess and compare competing methods [3].

This paper describes the testing, development, and evaluation of autonomous vehicles. In Section 2, there is a

brief discussion on elements of autonomous road driving

and the critical components of the intelligent system that

governs the vehicles behavior. In Section 3, concept for the

testing and evaluation of autonomous road driving systems

is presented. Section 4 briefly summarizes the technical

rationale behind this effort.

2. Autonomous Road Driving

As mentioned above, the archetypical autonomous vehicle is capable of operating within its domain for extended periods of time without human intervention, acting

in a manner that escalates the likelihood of successful

completion of the system’s intent or goals [4]. However,

as [5] expresses, designing an outdoor mobile robot to

follow a straight line is one thing; operating in a realistic

environment is another.
Real outdoor environments are stochastic, nondeterministic domains that contain countably infinite

combinations of percepts or sequences of situations [6].

Even road networks, which provide some structure in the

form of lane markings, signs, and rules that govern the

road, are still extremely complex [7]. The road networks

can be seen as multi-agent heterogeneous environments

that contain both static and dynamic obstacles.

The rationality of autonomous vehicles within any domain depends on the performance measures delineating the

criteria for success, a priori knowledge of the domain, plausible actions that can be performed, and in situ knowledge

perceived from the environment [6], [8]–[10]. This requires

that an autonomous road driving vehicle be a goal-directed

agent that is capable of applying situational awareness to

these multi-agent environments. For example, the vehicle

must be able to navigate intersections, avoid obstacles, and

follow the rules of the road in any weather or environmental

state. This highlights the need for an autonomous system to

contain a general theoretical model of intelligence that permits the integration of knowledge, perception, and behavior

generation into a unified framework [11].

Albus et al. [12, Chap. 2] provides a comprehensive

overview of reference architectures for intelligent systems.

Yet, the realization of an autonomous vehicle operating

safely and efficiently in a realistic on road driving domain

has not occurred. The ability for the mobile robot to “act

rationally” [6] in dynamic non-deterministic environments

is a central aspect to the evaluation of autonomous road

vehicles. [13] attributes the formulation of behaviors or

actions to the convergence of the ontological models,

or knowledge, with sequences of percepts. Thus, posing

the ability to gather knowledge in dynamic environments

that is accurate, reliable and current is necessary for the

development of rational behaviors [12], [14], [15]. This

has led to the identification of several key subsystems of

an autonomous road driving system that will serve as the

initial test elements to foster evolutionary standards and performance metrics to achieve the archetypical autonomous

system. The components of the autonomous system that

will initially be targeted are high-level control, low-level

control, and perception.

High-level control is an aspect of an autonomous vehicle that provides the system with long-term goals given

constraints on the system. Constraints are parameters that

are incorporated while generating behaviors that dictate

the selection of the appropriate routes and maneuvers on

the road, e.g., find the shortest path while obeying the

rules of the road. Therefore, high-level control is comprised

of a set of functions that use artifacts derived from a

knowledge base concerning the rules of the road and the

degree of aggressivity to formulate coarse path plans and

elementary maneuvers that the vehicle must perform to

achieve its ultimate goal. When an obstruction or obstacle

is encountered that renders the existing path plan obsolete,

the high-level control system must be able to re-evaluate

the situation to replan alternative routes and/or maneuvers.

Low-level control is an aspect of an autonomous vehicle

that provides the system with more immediate actions

or short-term goals. The low-level control system uses a

coarse path plan that is received from the high-level control

system to generate trajectories. The trajectories provide

the system with fine tuned aspects of autonomy such as

lane control and obstacle avoidance. In short, low-level

control provides the actuators of the vehicle with kinetically

viable trajectories that do not endanger the vehicle or

other elements within the environment [16]. Therefore, lowlevel control must account for the presence of both static

and dynamic obstacles and/or changing conditions in the

environment when generating these trajectories.

Outdoor environments in the real world present an enormous perception problem, given varying weather conditions, shadows, lighting conditions, etc. [5]. Perception

systems give the autonomous system the ability to detect

the edge of roads, read traffic signs, and track objects within

the environment. Sensory information is processed by the

perception systems in order to create a dynamic internal

representation of the real world environment. This representation is combined with ontological models to extract

knowledge to be used in the generation of appropriate

actions. This extracted knowledge is then combined with

a priori knowledge of the mode of operation to identify,

recognize, and predict objects within a time horizon of the

vehicle [12].

3. Program Concepts

The Intelligent System Division (ISD) at the National

Institute of Standards and Technology (NIST) has long

been a proponent of performance metrics for intelligent

systems. Under the DARPA Mobile Autonomous Robot

Software (MARS) program [17], [18], ISD is proposing

to construct a set of Autonomous Road Driving Arenas

(ARDA) to encourage the development of autonomous road

driving vehicles and the creation of community recognized

performance metrics for autonomous road driving. The

sharing of knowledge by the community has facilitated

rapid advancement of technologies and performance metrics within its domain. Therefore, this effort will attempt

to gather the participation of academic, government, and

commercial institutions through publications, technical reports, data sets, competitions, and accessibility to the arenas

themselves.

This effort will draw on experience from the development

and proliferation of the NIST Reference Test Arenas for

Autonomous Mobile Robots [19] and the associated formal

testing of urban search and rescue robots. The Urban

Search And Rescue (USAR) arenas originally provided

physical arenas to conduct controlled repeatable scenarios

that challenge the different facets of the USAR robots.

Since the inception of the USAR arenas, virtual components
and tools have been developed to simulate these arenas

[20]. Under the Mobility Open Architecture Simulation and

Tools (MOAST) [21], efforts are being made to seamlessly

integrate the real and virtual simulation environments into

a single simulation environment and toolset. In recent

years, the arenas have proven to be an invaluable resource,

lifting the standards of development within the community

by providing comprehensive data sets, publicly accessible

USAR arenas, and competitions such as RoboCup Rescue.

The Autonomous Road Driving Arenas (ARDA) will

provide an environment that will support the cost effective development and testing of critical components of

autonomous road driving vehicles. The ability to measure

performance in terms of efficiency, effectiveness, precision,

and reliability requires that the testing environment have

the ability to independently evaluate the various aspects

of autonomous road driving through various methods as

detailed by [22]. MOAST provides the reference framework

for the development of the facilities and tools to gather vital

information during repeatable trials, which can be used to

measure the performance of the autonomous vehicles both

quantitatively and qualitatively.

ARDA will provide a realistic, scaled world that will

evolve from simple lanes to a controlled dynamic environment that will exploit the capabilities and limitations

of autonomous road driving vehicles. Therefore, a standardized platform will also be developed that will support

these testing efforts by providing researchers with identical

physical capabilities for their algorithms to perform against.

It is important that ARDA provides the assurance that

all participants experience the same degree of difficulty

in order to measure and compare the performance of

intelligent autonomous vehicles [1].

The capabilities of ARDA will emerge in three phases.

Phase I will consist of a 2D planar arena with simple

controlled intersections and scripted traffic. In Phase II,

more complex environmental conditions, such as dynamic

changing lighting conditions, and more challenging traffic

conditions, such as construction zones, will be integrated

into ARDA. Phase III will complete ARDA by adding nonplanar road surfaces and other obscuring features such as

bridges, hills, and tunnels. At the end of each phase, a

technical report will be issued detailing the developmental

life cycle of each particular phase, including feasibility

analysis and technology assessment studies.

4. Technical Rationale

The rich world that exists within virtual simulation environments has long been an invaluable resource for the testing and development of intelligent systems. Traditionally,

these environments were developed in-house for specific

purposes [23]. More recently, there has been an emergence

of game-based simulation environments that capitalize on

the optimized rendering facilities and rich dynamic physic

models contained in professionally developed game engines

[24]. The Serious Games Initiative, USC’s Institute for

Creative Technologies, the MOVES Institute sponsored

by the US military and many others, illustrate the rapid

growth of the interest in the gaming community for robust

simulation packages.

Though the rich virtual worlds contained within these

simulation environments are invaluable, they are still not

the “magic bullet”. Algorithms that have been trained or

developed within the virtual environments can become

dependent on synthetic data cues. The majority of the

virtual simulation environments are built on deterministic

models that do not provide false alarms or missed detection

and employ unrealistic mobility models. However, virtual

environments do provide the flexibility and control in the

environment to evaluate the capabilities and limitations of

autonomous systems. This facilitates the ability to target

specific aspects of autonomous systems by decoupling critical components and logging vital data of an autonomous

system in repeatable trials.

Russell et al. [6] describes the environments contained

in the real world as stochastic, non-deterministic, dynamic,

multi-agent environments that are only partially observable

to any one agent. When implementing autonomous systems

on the actual platforms, the system must contend with

real mobility characteristics of the vehicle’s platforms. The

system must also rely on real sensors that provide noisy

data and missed detection. Thorpe et al. [5] express that

these environments force the development of algorithms

that are more robust and reliable in order for the system

to contend with the realistic mobility characteristics of the

actual platform and imperfect sensory data. However, the

real world environments also have drawbacks. Since the

planner relies heavily on the information obtained by the

perception system, the performance of the system is greatly

limited by what is known as the myopic planning effect

[25]. In short, the myopic planning effect is the limitation

of the planner to anticipate objects beyond the range of

the vehicle mobility sensors, e.g. LADAR (laser radar).

The inherent stochastic nature of real world environments

makes it difficult to perform repeatable trials that have the

same environmental state and conditions. Lastly, there is a

great concern to adhering to Isaac Asimov’s “Three Laws

of Robotics” (safety to itself and others) when using the

real world environments for the testing and evaluation of

autonomous vehicles.

The technical rationale behind this effort is to create an

environment that benefits from the best of both real and

virtual worlds and to create an array of incremental steps

that provide a smooth gradient to transition an autonomous

system from a purely virtual world to a entirely real world.

By allowing the virtual components and the real components to function where they perform best, ARDA seeks

to achieve an optimal testing environment that seamlessly

integrates both real and virtual components [21], [26], [27].

For example, Barbera et al. [28] describes a methodology
of reverse engineering performance metrics for sensors and

perception systems by evaluating the world model and

knowledge requirements needed for the behavior generation

systems. Therefore, in the ARDA environment the use of

virtual sensing can give us the opportunity to understand

what is better needed from a perception system. ARDA

will use the MOAST general-purpose framework to provide

this effort with a developmental reference model during

implementation.

MOAST manages the fidelity of the simulated worlds in

order to reduce the computational overhead that is inherent

in dynamic simulation environments. This is accomplished

by the concurrent use of the real vehicle platform, a highfidelity simulator and a low-fidelity simulator. An example

of the implementation of the MOAST framework is to use

the vehicle platform to run the low-level mobility, planning

and low-level perception, using a high fidelity simulator

to accurately simulate objects in the vehicles immediate

sphere of influence, and using a low-level simulator for

tracking, and simulating distant objects. Objects are automatically transferred between simulators as their proximity

to the vehicles changes within the MOAST framework.

This framework also permits the transparent transference

of data between real and virtual components, which gives

the developer the ability to toggle a “switch” between the

two components. For example, virtual sensor that simulate

raw sensory data or real sensors can be used as input into

a perception system which in turn can either be an actual

functioning subsystem or a virtual system that simple places

preprocessed knowledge into the WM.

ARDA will provide an environment, with extensive highresolution data sets of annotated maps, features, and a priori

knowledge to implement the MOAST framework. This will

provide ground truth and a benchmark for the testing,

development, and evaluation of the intelligent systems in

this specific domain. A scaled physical model of a road network will be used to initially evaluate high-level planning,

low-level mobility, and low-level perception. Later, this

environment will be used in the testing and development of

multiple agent systems (MAS) [24], essential components

such as various levels of Situational Awareness [29], and

axioms of cooperation such as distributed artificial intelligence, resource conflicts, learning, group architectures, and

geometric problems [30] .

ARDA will leverage existing technologies and on-going

efforts in simulation to construct a simulation environment

based on the MOAST framework consisting of four basic components: Real World Arenas, Virtual Simulation

Worlds, Vehicle Platforms, and a Tracking System. The real

world arenas will be the physical world where the vehicle

platforms will be used to test various aspects of autonomous

systems. The virtual simulation environment will reflect

the real world environment and will utilize information

captured by the tracking system in order to provide ARDA

with an array of visualization tools and services. Tracking

will also be used to provide navigation and other vital

data to the agents operating within the arenas. These four

components will be detailed further in the following subsections.

4.1. Real World Arenas

ARDA implements the MOAST framework in a onetenth scaled replica of a real environment that includes

objects and features such as plants, buildings and roads.

The arena design will provide an equal level of difficulty

for every autonomous system operating in ARDA. The

arenas will target specific aspects of the autonomous system

by mimicking the environmental conditions found in the

on-road driving domain. These environmental conditions

include static and dynamic objects, variable weather and

lighting conditions, and features associated with road networks, e.g. controlled intersections and lane markings.

The initial configuration of the arena will consist of a

planar world with limited environmental conditions. More

complex environmental conditions will be incrementally

introduced in response to the escalating capabilities of the

autonomous road driving systems.

Essential design factors that will continually be considered will be the use of commercially available components,

modularity, reconfigurability, and durability. Commercially

available components are standardized parts that are readily available and relatively inexpensive. The use of these

components will assist in the proliferation of the arenas

by allowing participants to construct or repair their own

replicas according to ARDA’s specs. The consistency of

the standardized components expedites rapid repairs while

maintaining the arena’s integrity. A modular design also

assists in efficient repairs through the easy replacement of

damaged components. Reconfigurability is the ease with

which environmental features can be added, modified, or

deleted from the arenas. This gives ARDA the versatility

to alter the configuration of its constituent components in

order to target different aspects of the autonomy. Reconfigurability facilitates different road network implementations

ranging from small demonstration configurations to large

competition networks. Durability refers to the resilience of

the arenas to the continual weathering due to the environmental conditions and the stress of assembly/disassembly

and packing/unpacking associated with frequent travel.

With the design criteria in mind, ARDA will be composed of inter-locking rectangular frames with attached

panels to create the base, upon which the road networks

will be placed. The primary members of the road network

frames will potentially be aluminum extrusion. Several

types of commercially available aluminum extrusion are

easily machined to provide unlimited attachment solutions.

Plastic panels that are durable and lightweight will be

tailored to conform to the frame and will provide the road

surface and the foundation upon which terrain features will

be placed. Upon the construction of the base, various terrain
objects and artificial turf will be used to populate the world.

Lane markings will be painted on the road surface to create

passing and non-passing zones. Controlled intersections

will be composed of traffic signs and/or traffic lights. Traffic

lights will be controlled through basic transistor logic or

through interfaces to the virtual simulation controller.

4.2. Vehicle Platforms

All vehicle platforms that conform to the one-tenth

scaled environment will be permitted to compete in ARDA.

However, standardized platforms will be developed for use

in ARDA that are akin to modified remote control cars

(popular with hobbyists). For these platforms to behave

rationally, the platforms must extend their computational

capabilities to achieve the capabilities and computational

specs currently available in an implementation of an actual

autonomous vehicle, such as the NIST High Mobility

Multipurpose Wheeled Vehicle (HMMWV) [31]. This requires that the platforms contain sufficient computational

power, control architecture, sensors, and communication

bandwidth. Initially, a few criteria will be used to evaluate

the platform’s design. The criteria identified to maximize

the platform’s capabilities are:

• Reference Control Architecture

• Standardized Parts

• Computational Power

• Battery-Life vs. Power Consumption

• Communication

• Sensors

• Closed-Loop Controller for Actuators, Sensors, and

Communication

1) Reference Control Architecture: It is critical to

identify a reference model architecture to organize the

hardware and software within an intelligent system. The

Real-Time Control System architecture, RCS, was chosen

for the platforms in the ARDA because it uses a modular,

hierarchical control architecture as an efficient way to manage the system’s complexity. RCS is a real-time, distributed,

hierarchical architecture that consists of computational

nodes with well-defined functional components and clearly

defined interfaces. RCS contains a systematic regularity

so that each control node in the hierarchy performs the

same general type of functions: sensory processing (SP),

world modeling (WM), value judgment (VJ), and behavior

generation (BG).

The principal difference between control nodes at the

same level is in the set of resources managed, while the

principal difference between nodes at different levels is in

the knowledge requirements and the fidelity of the planning

space. This regularity in the structure enables flexibility in

the system architecture that allows scaling of the system to

any arbitrary size or level of complexity. [1]

Each level in RCS has a characteristic range and resolution in space and time, determined by the specific implementation requirements. Each level has characteristic tasks

and plans, knowledge requirements, values, and rules for

decision-making. Every module in each level has a limited

span of control, a limited number of tasks to perform, a

limited number of resources to manage, a limited number

of skills to master, a limited planning horizon, and a limited

amount of detail with which to cope [32].

2) Standardized Parts: The standardized vehicle platforms developed for ARDA will be modified one-tenth

scaled model remote control (RC) cars. Standard offthe-shelf parts, e.g. chassis, wheels, suspension and servos/actuators, will provide the base hardware for the vehicle platforms. These parts for these RC cars are widely

available, inexpensive, and standardized allowing for vehicles to be modified easily. This facilitates efficient repairs

and construction of vehicles platforms, which is ideal for

development and testing of this nature. This effort will

capitalize on available internal programs, competitions, and

partnerships to develop a standardized platform that will

provide the optimal functionality within ARDA.

3) Computational Power: Each platform must have sufficient computational power to handle the computational

load of the autonomous systems, e.g. low-level planner,

high-level planner, and low-level perception systems. The

MOAST framework and modular hierarchical design of

RCS allows for standard low-power single board coreprocessing units to be coupled through the designated

interfaces with off-board processing power to meet any

computational load needed by the vehicle. This provides

the environment the flexibility to distribute the autonomous

system’s components or subsystems between the onboard

and off-board processing units.

4) Battery-life vs. Power Consumption: The vehicle platforms will not be tethered; therefore, their electrical systems

must operate on battery power. This bounds the time that

the vehicles will be able to operate in ARDA. This requires

that battery packs provide a significant number of milli-amp

hours (mAH) to effectively operate the vehicle’s electrical

system, without signifigant power loss, for a duration of

time that is appropriate for testing. For example, the coreprocessing units available are 12 W systems, drawing 1.75

V. RC battery packs are available in a 6-cell battery back

(9 V) that provide 3000 mAh, which equate to 3 Ah. Given

the power requirements of the core-processing unit and

additional TTL logic required, the system would draw one

amp from the battery pack. This only gives the vehicle three

hours of operation before the power supply would need to

be recharged. This does not take into account the power

requirements to operate the motor, servos, or additional

hardware that may need to be added for sensing. Multiple

batteries can be mounted on the platform that provides

ample power for the vehicle’s electrical system.

5) Communication: Again, the combination of the

MOAST framework and RCS lends flexibility to distribute

the components of the autonomous system between the

onboard and off-board processing units. The interfaces

between the distributed subsystems, command and con-
trol channels, require enough communication bandwidth

to accommodate a wide range of command messages.

The communication infrastructure of ARDA must also be

able to handle the command and control interfaces for

multiple vehicles and broadcast global information, such

as navigation data.

6) Sensors: Intelligent systems gather knowledge about

the state of the world and its relation to the world through

sequential percepts captured through sensors. Sensing capabilities within the MOAST framework can either be

obtained virtually or through real onboard sensors. These

capabilities include the collection of navigation data, color

video, and range finding information. In the scaled environment of ARDA, objects will remain proportionally scaled

to their real world counterparts, requiring sub-centimeter

resolution in the sensory information. During the first phase

of the development, the vehicle platforms will rely heavily

on virtual sensing. The vehicle platforms will be designed

with appropriate interfaces that will facilitate the addition

and/or re-configuration of real onboard sensors.

7) Closed-Loop Controller for Actuators, Sensors, and

Communication: The architecture controlling the sensors, actuators and communications will rely on a coreprocessing unit for its computational requirements. Closedloop adaptive controllers will provide the core-processing

unit with control interfaces and added computational power

to regulate its facilities. This provides each distinct facility

with a closed communication control loop that is comprised

of a command sent to the controller, feedback received

from the controller, and data transference between the coreprocessing unit and the controlled facility. Each control

loop will consist of a stacked I/O card that contains additional computational power to run small control programs.

4.3. Virtual Simulation Envirnoment

Within the MOAST architecture, virtual and real components are combined transparently to mutually augment

each other in order to achieve an environment conducive

for the evaluation of autonomous road driving vehicles.

This effort requires the virtual simulation environment to

be capable of handling the overhead of simulating complex,

unstructured environments contained in road networks. The

virtual environments will be required to provide multiple

levels of resolution, e.g., in the sphere of influence around

the vehicle the virtual simulator must have high fidelity,

while the distant objects require less fidelity.

The virtual simulation environments must provide the

facilities and interfaces to allow for the developer to create

new worlds, provide virtual sensing capabilities, modify

objects, and appropriate command and control channels

to interface with all agents in both the real and virtual

environments [33], [34]. The virtual world must also provide the facilities to log vital information in real-time

and visualization tools to access and display the internal

state of the vehicle during operation. These tools provide

developers with a level of control that permits for the

internal state of the vehicle to be modified. For example,

a vehicle will perceive virtual objects as actual objects

in the real world, where the virtual world will view the

vehicle as another agent within the virtual world. Having

these tools to visualize the internal state of the autonomous

system in real-time gives the developer more insight into

the decision making process and the causality of behaviors

being produced.

The virtual simulation environments must also be able to

provide realistic mobility characteristics, sensory data, and

tactical behaviors for each vehicle. Dixon et al. [26] points

out that a signifigent amount of low-level infrastructure is

required to support the communication, control, and simulation of multiple agents in high-fidelity virtual environments.

The low-level infrastructure is time-consuming and requires

that the developer have a high-level of expertise to maintain

the infrastructure [35]. It appears that there is a positive,

non-linear correlation between the number of objects in the

world and the computational load to simulate these objects.

An effective way to manage the computational complexities

within these virtual environments is to couple a high-fidelity

simulator with a low-fidelity simulator. The high-fidelity

simulation provides very accurate information about objects

in a bounded region, where as the low-fidelity simulation

simulates the behavior and sensing of a larger area of distant

objects at a lower resolution. This provides the autonomous

system with in situ knowledge at an appropriate resolution,

while orchestrating the entire scenario at a lower, more

efficient resolution.

4.4. Tracking System

A tracking system will be integrated in the arenas to

collect real-time navigation data of all the subjects in the

real world environment and broadcast this knowledge to all

the constituents that comprise ARDA. This knowledge can

serve as a virtual positioning sensor for each vehicle or can

be coupled with a priori ground truth knowledge to provide

other virtual sensing capabilities. It can provide redundant

navigation information for each platform by being coupled

with wheel encoders or other positioning sensors located

on the actual vehicle. The tracking system logs this data

so that is can be used for the evaluation of the behaviors

generated by the autonomous vehicles. This positioning

knowledge can be compared with positioning information

logged from the vehicle to validate trajectories and coarse

path plans. These options are being explored based upon the

available platform sensors and current resolution, accuracy,

and update rate limitations of available tracking systems.

Overhead, two-dimensional camera tracking is being

considered as the initial tracking system due to the planar

configuration in ARDA’s real world environment. The technologies available in commercially available color video

cameras/camcorders provide sufficient resolution and updates rates to serve as the overhead visual sensor for the
tracking system. Many publicly available vision algorithms

can be mated with most overhead cameras to provide

tracking update rates of 30 Hz or slightly greater. One such

available software package is Mezzanine [36]. This highly

competent overhead visual tracking software is publicly

available at no cost and may be used with almost any

video camera/camcorder. The software enables the camera

to track objects by following color-coded fiducials placed

on top of each autonomous vehicle platform. Mezzanine

provides real-time translation of pixel location into world

coordinates.

Other software is widely available for camera tracking

including algorithms developed by the RoboCup Soccer

Small-Size Teams for use in their annual competitions

[37]. This league features teams of five robots playing

soccer against one another where all necessary sensing and

processing takes place off-board. Each team sets up an

overhead camera and places their own color-coded fiducials

on their robots. Teams utilize their own tracking algorithms

so that they may locate the position and orientation of their

robots, their opponents, along with the position of the ball.

The off-board computational facilities process this data and

send the appropriate commands back to their robots. Several

teams have extensively documented their vision algorithms

that have the potential to be used with ARDA [38]–[40].

5. Summary

Under the DARPA MARS project, the Intelligent Systems Division of the National Institute of Standards and

Technology is proposing the construction of a real/virtual

simulation environment for the performance evaluation of

autonomous road driving vehicles, ARDA. The effort is

seeking to coalesce together an autonomous road driving

community that will support the development, testing,

and evaluation of various implementations of autonomous

systems. ARDA will be designed to support the MOAST

framework, which will give the developers the ability

to target specific aspects of autonomous road driving in

repeatable scenarios. This effort hopes for the realization

of an intelligent autonomous system that will service as the

archetypal system, which all other systems will be modeled

and compared.

6. Acknowledgement

This work was supported in part by the Army Research

Lab’s program in unmanned vehicles (PM. C. Shoemaker)

and DARPA’s Mobile Autonomous Robotic Software program (PM. D. Gage).

7. Product Disclaimer

Commercial equipment and materials are identified in

order to adequately specify certain procedures. In no case

does such identification imply recommendation or endorsement by the National Institute of Standards and Technology,

nor does it imply that the material or equipment identified

are necessarily the best available for the purpose.

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2003.
 1 

Software Tools for Design and Performance Evaluation of Intelligent 

Systems 

S. Joshi, M. Slicker, A. Surianarayan 

Pathway Technologies Incorporated 

Blue Bell, PA 19422 

ABSTRACT 

The objective of this effort was to leverage the 

principles of knowledge engineering in the ongoing 

development of a software tool for rapid design, simulation, 

prototyping and performance evaluation of Intelligent 

Systems in the Matlab/Simulink environment. In this paper, 

we have demonstrated the use of this software tool to design 

a cable robot, automatically generate the kinematic and 

dynamic relationships for this robot and develop an 

automatic on-line calibration scheme for this cable robot 

where traditional one-time or periodic calibration methods 

do not provide adequate measures of performance. Hence, 

from the standpoint of intelligent system design and 

performance metrics, through this example, we demonstrate 

the usefulness of leveraging the principles of knowledge 

engineering to develop domain specific knowledge. The 

models so developed can be used to evaluate the 

performance of such robotic systems and modified to 

improve the performance. For example, kinematic errors 

such as assembly errors are likely to be introduced in the 

construction; faults such as joint failures are likely to be 

introduced in the operation. Hence, automated on-line 

calibration of intelligent systems (such cable robots) 

becomes particularly important for continuous performance 

evaluation (positioning accuracy) and enhancement. 

Keywords: Intelligent system design, Cable robot, Kinematic 

modeling, optimization

1. INTRODUCTION 

The NIST intelligent systems division (ISD) has 

employed a generic shell approach to facilitate the 

development of intelligent real-time control (RCS) systems. 

The RCS approach/architecture organizes the elements of 

intelligence to create functional relationships and 

information flow across the various levels, of a hierarchy, 

that have assigned responsibilities. In this context, 

knowledge is one of the cornerstones of intelligent real-time 

control system design and implementation. In this work we 

have shown how knowledge can be used for performance 

evaluation and enhancement of intelligent real-time systems 

(such as robotic systems). 

The objective of this effort was to build upon previous 

work done by the authors on calibration of cable robots and 

conduct case study to demonstrate the use of robotics toolkit 

software developed at Pathway Technologies Inc to rapidly 

design a cable robot, transition seamlessly to controller 

design, target implementation and set up an automatic online calibration scheme for this cable robot where traditional 

one-time or periodic calibration methods do not provide 

adequate measures of performance. Hence, from the 

standpoint of intelligent system design and performance 

metrics, through this example, we demonstrate the need for 

automated on-line calibration of intelligent systems (cable 

robots) so that repetitive manual calibration can be 

minimized. A flowchart summarizing our approach is 

shown in Figure 1. Starting out from the development of a 

graphical model of the cable robot in a GUI, we generate 

the governing kinematic equations of the cable robot and 

then automatically generate a SimMechanics model of this 

system, then a set of kinematic parameters is selected for 

identification. It is well known that for some calibration 

methods, all the kinematic/geometric parameters cannot be 

identified: some of them have no effect on the calibration 

model, and some others are grouped together [2]. Hence, a 

parameter identifiability analysis is performed to make sure 

that all geometric / kinematic parameters can be identified 

uniquely. Once the parameter identifiability is ascertained, a 

set of configurations to be used for calibration and 

validation are selected. Note that the kinematic parameter 

identifiability Jacobian can also be used for the purpose of 

optimal pose selection in calibration of the cable robot. The 

calibration problem is then set up as a nonlinear 

optimization problem and is solved by using the nonlinear 

least squares estimator available in the robotics toolkit. The 

corrected kinematic model obtained from the optimization 

procedure is then validated using simulation data. 

The 6-DOF cable robot, whose calibration we have 

studied in detail in this report is a closed-chain mechanism 

in which the mobile platform is connected to the fixed base 

by six variable length cables. Such cable robots offer the 

advantages of a larger workspace and low weight with the 

disadvantage that the cables can apply forces only when in 

tension. The join of each of these cables with the fixed and 

the moving platforms are kinematically equivalent to and 

are modeled as passive spherical joints. Whereas the cable 

can be modeled as a prismatic joint that can apply forces in 

one direction only. A typical control strategy for such cable 

robots is to specify the pose of the moving platform in some 

world coordinate frame and then to use the inverse 

kinematics relationship to solve for the cable lengths. The 

accuracy of the moving platform location critically depends 

upon the kinematic model of the cable robot that resides in 

the robot controller. The kinematic calibration of such 

parallel mechanisms improves the accuracy of the moving 

platform through modification of the manipulator kinematic 

model. 
 2 

Calibration of a general parallel manipulator normally 

encompasses the following tasks: 

1. Kinematic modeling of the platform to account for 

major error sources. 

2. Measurement of platform poses 

3. Identification of the kinematic error parameters of 

the platform by use of the measurement data. 

4. Accuracy compensation of the platform by use of 

the identified error parameters. 

The kinematic calibration procedure presented in this 

paper can be classified as a classical calibration can be 

classified as a classical calibration technique [1, 2, 3, 4, 9, 

10] as opposed to self-calibration methods [6, 7, 8]. The 

method of kinematic calibration used in this work was 

presented earlier in detail by the authors [11]. It requires the 

measurement of moving platform orientation by using two 

inclinometers and the measurement of cable lengths. The 

authors had considered the following geometric parameters 

in their calibration: coordinates of the cable joins on the 

fixed and moving platforms (36 parameters), offsets of the 

cable lengths (6 parameters) and error on the 

perpendicularity of the two inclinometers (1 parameter). 

However, the coordinate systems on the base and moving 

platforms are placed in such a fashion that 8 out of the 36 

geometric parameters are equal to 0. Remaining 28 

parameters are constant and may not be equal to zero in 

general. Aim of the calibration process is to compute the 

exact values of these 28 parameters, those of the 6 offsets of 

the prismatic joints, and the error angle on the 

perpendicularity of the two inclinometers. 

Organization of the technical part of the paper is as 

follows: In the next section we will talk about knowledge 

representation and the significance of domain specific 

knowledge in the design and performance evaluation of 

intelligent systems, followed by the software architecture 

and then the specifics of the calibration and optimization 

problems studied here. Finally we present some results 

obtained from simulation studies. 

2. KNOWLEDGE REPRESENTATION

Large-scale intelligent systems design can benefit from 

existing domain specific knowledge from various 

disciplines through knowledge engineering processes. In 

this context, based on the broad definition of knowledge, 

components of knowledge can be broadly classified in to 

symbolic, iconic, and parametric [12]. For example in the 

area of parametric knowledge, system models are generated 

based upon analytical principles such as physics based 

equations of motions, empirical modeling based upon maps, 

and system identification based on non-linear input-output 

system relationships which are difficult to quantify using 

analytical relationships. In the area of symbolic knowledge, 

system models are generated based upon mathematical 

logic, frames, rules, and semantic nets and such. In 

traditional AI systems there is a larger emphasis on 

symbolic knowledge whereas in traditional intelligent 

control there is a greater emphasis on parametric 

Automated Modeling 

(Kinematics/Dynamics) 

Robot Instrumentation 

Kinematic Parameter Identifiability Analysis

Optimal Pose Selection 

Experimental Work: 

Gather sensor data at 

selected platform 

poses 

Compute theoretical 

sensor data based upon 

Nominal Kinematic 

Model 

Estimation: Nonlinear Optimization 

Model Validation 

Figure 1: Cable robot calibration process

Design Cable Robot in GUI 

Figure 2: Various activities related to robotics domain

 WORK CELL

Individual Robot

Servo

Actuator Control Signals

Primitive Level

Trajectory Planning

Optimization

Knowledge 

Kinematics

Knowledge 

Controls 

Knowledge
 3 

knowledge. In the context of 4D/RCS, based on the four key 

paradigms, this would mean that in the lower levels of the 

hierarchy, such as, servo there is a greater emphasis on 

parametric knowledge whereas higher level planning nodes 

the emphasis is on symbolic knowledge. Figure 2 shows the 

hierarchy of various activities carried out in the operation of 

a robotic work-cell and the types of knowledge associated 

with these tasks. In the robotics toolkit we deal mostly with 

parametric knowledge such as that required for kinematics, 

dynamics, and optimization. 

3. DOMAIN SPECIFIC KNOWLEDGE: 

KINEMATIC MODELING 

Numerous definitions of intelligence found in literature 

make references to knowledge. However, very little 

literature is available which addresses the questions what is 

the needed knowledge in intelligent systems? and, how to 

generate and represent this knowledge?[12]. In this context, 

one of the key objectives of this work was to develop or 

build domain specific knowledge in the areas of (i) 

Kinematics, (ii) Dynamics, (iii) Path Planning, (iv) Control 

System Design and Implementation, (v) System 

Identification and Adaptive Behavior, and (vi) Numerical 

Optimization techniques for real-time implementation. So 

far kinematics, dynamics, and planning, knowledge has 

been developed. 

Another important aspect of the development process is 

a need to have structured approach to developing domain 

specific knowledge. Figure (3) shows an example wherein 

under the category kinematics, we define class consisting of 

different types of dynamical systems such as sceleronomic 

and rheonomic systems. Under each classification, it is 

possible to specify subclasses, namely, in the case of 

Sceleronomic Systems, the different types include 

holonomic and non-holonomic systems. Such a structured 

approach to system classification leads to an evolutionary 

approach to building knowledge base. In the following 

paragraph we have outlined the development of kinematics 

related domain specific knowledge and the development of 

kinematic models of the cable robot under study. 

Kinematics deals with the constraints on the spatial 

motions of various bodies within a system. One possible 

classification of kinematic systems is presented in Figure 3. 

This classification will enable us to design and develop 

apriori knowledge repositories for various classes of 

kinematic systems. At Pathway Technologies we have done 

some preliminary research in this area. We have developed 

a unified methodology to generate the kinematic maps for a 

class of robots that can be classified as sceleronomic, 

holonomic systems. By making use of the D-H and 

Klienfinger notations we have been able to develop 

algorithms for generating the kinematics of such systems on 

the fly. We have thus succeeded in capturing some expert 

knowledge in this domain area. A user of our system who 

wants to design a robot can have all kinematic relations of 

the robot generated for him without his writing a single 

equation. In the event of situations like joint failures, we can 

recompute the kinematics for the robot with one less degree 

of freedom as compared with the normal operating 

conditions. The kinematic planners can then plan 

trajectories accordingly. During hardware operation we can 

lock the failed joint and continue operations with reduced 

degrees of freedom. Figure 4 shows a screenshot of the 

cable robot designed with the robotics toolkit. 

Figure 4: The robotics toolkit generates kinematic maps on 

the fly. 

A schematic of the 6-DOF cable robot studied in this 

report is shown in Figure 5. A coordinate system A: xyz is 

attached to the fixed platform and another coordinate frame 

B: uvw is attached to the moving platform. The inverse 

kinematic model (IKM) which calculates the leg lengths 

vector for a given Tr, which is the homogeneous 

transformation matrix from frame B to frame A, is easy to 

obtain. On the contrary, the direct kinematic model (DKM) 

which calculates the moving platform location Tr as a 

function of given cable lengths vector, is difficult to obtain 

analytically. A numerical iterative method based on the 

inverse Jacobian matrix of the cable robot is used to find a 

SCELERONOMIC RHEONOMIC

HOLONOMIC

ALGEBRAIC 

EQUATIONS 

FORWARD KINEMATICS 

CLOSED-FORM 

NON-HOLONOMIC

DIFFERENTIAL 

EQUATIONS 

KINEMATICS 

Figure 3: Classification of kinematic systems 
 4 

local solution to the direct kinematics problem. For the 

purpose of solving the direct kinematics problem we have 

used a general algorithm which can solve the direct 

kinematics of any general robot manipulator (serial, parallel, 

or hybrid). This algorithm converges rapidly and can be 

summarized as follows: 

1. Input the actuated joint variable values, qa, the initial 

guess values on the moving platform location, Tr, and the 

passive joint variable values, qp. 

2. Solve the kinematic constraints for the manipulator to 

compute the actual passive joint variable values, qp. 

3. Calculate the corresponding moving platform location by 

solving the forward kinematics of any limb of the parallel 

manipulator and update the initial guess on the moving 

platform location. 

Where Tr is a homogeneous matrix that defines the 

location of the moving platform with respect to the base 

coordinate frame and qa is the given vector of cable lengths. 

4. SOFTWARE ARCHITECTURE 

We have developed an interactive 3D environment for 

viewing serial and parallel robot models described in text 

form, constructing robot models and robotic workcells, 

positioning and posing robots, specifying tasks and endeffector trajectories, and visualizing robots performing tasks 

and trajectories through time-based animation. Figure 4 

illustrates the view of the workcell as seen by the user. 

For the purpose of simulating the dynamics of robotic 

workcells, and implementing robot controllers, the resulting 

models built using the interactive 3D environment can be 

exported to the Simulink environment. Robots are modeled 

in terms of SimMechanics blocks, trajectories as a sequence 

of end-effector positions/orientations, kinematics as Sfunction blocks written in the C language. Models of joint 

control and actuation can be further elaborated by the user 

or can be chosen from models already developed. 

Synchronization is provided between the model built in the 

interactive 3D environment and model elaborated in 

Simulink environment. The tight integration of the Simulink 

environment and the interactive 3D view enables the rapid 

development of robotic workcells. 

In addition to automatic generation of kinematic 

models for serial and parallel robots, our tool supports the 

automatic generation of calibration models. The 

position/orientation of the end-effector is estimated in the 

controller, and if the difference from the expected 

position/orientation is significant the robot controller can 

automatically recalibrate itself, and derive a new kinematic 

model. As the recalibration computation in non-trivial this 

part of the model can be partitioned and implemented on a 

host PC connected to the robot controller. 

Performance of the model can be evaluated by taking 

the difference between the actual path taken in both 

simulation and experiment and the path that is specified in 

the 3D environment. Experiments can be constructed such 

that the performance can be measured over a range of 

working conditions. One expected source of decalibration is 

assembly errors that modify the kinematics of the robot. The 

results of the simulation and can be stored on the permanent 

storage of system for further study or they can visualized in 

through 3D animation. 

5. CABLE ROBOT CALIBRATION MODEL 

 By making use of the direct kinematic model of the 

cable robot we can calculate the orientation of the moving 

platform with respect to some coordinate frame A: xyz as a 

function of cable lengths and the nominal values of the 

geometric parameters. In this work we will demonstrate an 

approach to calibrate this 6-DOF cable robot using two 

inclinometers mounted on the moving platform of the cable 

robot. This calibration procedure follows the approach 

proposed by Besnard and Khalil [1] for the calibration of 

Stewart Platform using two inclinometers. 

Following Besnard and Khalil [1] we consider that 

there is an error angle γ on the perpendicularity of the two 

inclinometers. Hence then inclinometer angle values are: 

The angle γ is unknown and it can be included in the 

parameters to be calibrated. In the calculations presented in 

this paper we have assumed the two inclinometers to be 

perfectly perpendicular and hence γ is identically equal to 

zero. 

sin ( T (3,2) - T (3,1)sin ) (1)

sin ( T (3,1) )

1

2

1

1

α γ

α

r r

r

−

−

=

=

A3, A4

B2, B3

B4, B5

B6, B1

Figure 5: A Six DOF cable robot

A1, A2

Fixed Platform 

Moving Platform 

Cables

A5, A6
 5 

6. OPTIMIZATION 

 The inclinometer values are calculated for each of 

the k robot manipulator configurations using Equation (1) as 

function of the nominal geometric parameters and the cable 

lengths: 

where n n n T

m [ , ] Φ = α 1α 2 is the vector of computed 

inclinometer values at the nth moving platform location, ζm 

is the 35x1 vector of nominal values of the robot geometric 

parameters. 

Similarly we define the vector n Φr of the measured 

inclinometer values (real) for the nth manipulator pose. If the 

model is exact, the angles calculated and measured must 

have the same values at any arbitrary moving platform pose: 

Using k configurations, the geometric parameters are 

identified such that F = min , with 

This least squares estimation based nonlinear problem was 

solved by an estimation algorithm that is a part of the 

robotics toolkit software. 

7. SIMULATION PROCEDURE AND 

RESULTS 

We simulated the calibration method on a cable robot 

whose nominal parameter and real parameters are given in 

Table 1 through Table 4. At present we do not possess any 

consistent (real) sensor data to validate our calibration 

model. We hope to acquire some field data in the near 

future. This will enable us to check the accuracy of 

calibration and also validate the calibration procedure. 

Table 1 Nominal values of cable attachment points at the 

Base platform in the fixed coordinate frame. 

x y z 

baseA1 0 0 0 

baseA2 0 0 0 

baseA3 0.8189 0 0 

baseA4 0.8189 0 0 

baseA5 0.4095 0.7092 0 

baseA6 0.4095 0.7092 0 

Table 2 Real values of cable attachment points at the 

Base platform in the fixed coordinate frame. 

x y z 

baseA1 0 0 0 

baseA2 0.01 0 -0.009 

baseA3 0.8312 -0.01 0.0043 

baseA4 0.7989 0.03 0.0147 

baseA5 0.4275 0.6792 0.004 

baseA6 0.3858 0.7302 -0.03 

Table 3 Nominal values of cable attachment points at the 

Moving platform in the Moving coordinate frame 

x Y z 

movingB1 0 0 0 

movingB2 0.2572 0 0 

movingB3 0.2572 0 0 

movingB4 0.1286 0.2228 0 

movingB5 0.1286 0.2228 0 

movingB6 0 0 0 

Table 4 Real values of the cable attachment points at the 

Moving Platform in the Moving coordinate frame. 

x Y Z 

movingB1 0 0 0 

movingB2 0.2770 0 -0.052 

movingB3 0.2472 0.05 0.02 

movingB4 0.1716 0.2028 0.1 

movingB5 0.1076 0.2398 -0.03 

movingB6 0.04 -0.03 -0.05 

The procedure used to generate the simulation 

configurations can be summarized as follows: 

1. Generate m random sets of cable lengths. 

2. Select n sets of cable lengths from the m for which 

the moving platform lies within the manipulator 

workspace. Further, select k sets of cable lengths 

from the n that have that lowest condition numbers 

for the Identification Jacobian matrix. 

3. Compute the inclinometer values using the forward 

kinematics solution. 

4. Add some random numbers on the nominal 

inclinometer values to generate a set of data that 

we would term as the real sensor readings. 

5. Compute the objective function for the purpose of 

optimization using these sets of the so-called real 

and computed inclinometer values. 

- 0 for i 1, 2, ..... n ....... k (3) i

r

i Φm Φ = =

 (4)

- 1 1

⎥

⎥

⎥

⎦

⎤

⎢

⎢

⎢

⎣

⎡

Φ −Φ

Φ Φ

=

k

r

k

m

m r

F M

( , ) (2) m

n n

m Φ = f q ζ
 6 

6. Solve the nonlinear optimization problem using the 

Robotics Toolkit. 

7. Compute the real geometric parameters for the 

robot under consideration. 

6. SUMMARY 

In summary, we present the features of our robotics 

toolkit software and the support it provides for the 

performance evaluation and performance enhancement of 

intelligent systems. This toolkit allows designers to build 

robots and robotic work-cells rapidly in a graphical 

environment, automatically generates the kinematic model 

and dynamics (using SimMechanics) of such intelligent 

systems and provides support for performance evaluation 

and enhancement. In addition, the use of Matlab/Simulink 

environment helps control designers to transition seamlessly 

from design to hardware. We also present a case study to 

illustrate the use of this software to rapidly deploy an 

automatic kinematic calibration method that allows the 

intelligent system (cable robot) to precisely manipulate its 

surroundings. Simulation studies can be conducted off-line 

and sensitivity of the positioning performance to various 

geometric parameters can be studied in a virtual 

environment. Also, the presented continuous on-line 

calibration approach provides performance improvement 

over the conventional periodic calibration methods as it 

continuously compensates for mechanical changes to the 

system. This improved system behavior provides 

quantitative measures of performance improvement. 

ACKNOWLEDGEMENTS 

Development of the robotics toolkit was funded in part 

by NIST under an SBIR. The authors wish to thank Elena 

Messina of NIST for valuable comments. 

REFERENCES 

[1] Besnard, S., and Khalil, W., “Calibration of Parallel 

Robots Using Two Inclinometers,” Proceedings of the 

IEEE International Conference on Robotics and 

Automation, May 1999. 

[2] Besnard, S., and Khalil, W., “Identifiable Parameters of 

Parallel Robots Kinematics Calibration,” Proceedings 

of the IEEE International Conference on Robotics and 

Automation, May 2001. 

[3] Yang, G., Chen, I. M., Lim, W. K., and Yeo, S. H., 

“Self-calibration of Three-Legged Modular 

Reconfigurable Parallel Robots Based on Leg-End 

Distance Errors,” Robotica, Vol. 19, pp. 187-198. 

[4] Irascu, C. C., and Park, F. C., “Geometric algorithms 

for Closed Chain Kinematic Calibration,” Proceedings 

of the IEEE International Conference on Robotics and 

Automation, May 1999. 

[5] Zhuang, H., and Liu, L., “Self-calibration of a Class of 

Parallel Manipulators,” Proceedings of the IEEE 

International Conference on Robotics and Automation, 

April 1996. 

[6] Besnard, S., and Khalil, W., “Self-Calibration of 

Stewart-Gough Parallel Robots Without Extra 

Sensors,” IEEE Transactions on Robotics and 

Automation, Vol. 15, No. 6, December 1999. 

[7] Zhuang, H., and Roth, Z., “Method for Kinematic 

Calibration of Stewart Platforms,” Journal of Robotic 

Systems, 10(3), pp. 391-405, 1993. 

[8] Zhuang, H., Yan, J, and Masory, O., “Calibration of 

Stewart Platforms and Other Parallel Manipulators by 

Minimizing Inverse Kinematic Residuals,” Journal of 

Robotic Systems, 15(7), pp.395-405, 1998. 

[9] Lintott, A. B., and Dunlop, G. R., “Parallel Topology 

Robot Calibration,” Robotica. 

[10] Vischer, P., and Clavel, R., “Kinematic Calibration 

of the Parallel Delta Robot,” Robotica, Vol. 16, pp.207-

218, 1998.

[11] Joshi, S.A., and Surianarayan, A., “Calibration of a 

6-DOF Cable Robot Using Two Inclinometers,” 

Proceedings of the PerMIS 2003 Conference, 

Gaithersburg, MD.

[12] Messina, E., Albus, J., Schlenoff, C., and Evans, J., 

“Knowledge Engineering for Real Time Intelligent 

Control”, Proceedings of the International Workshop on 

Knowledge Management Techniques, Krema, Italy, 

2002.

	
 

 	  	
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Negative Knowledge and Rational Creativity 

Mark H. Bickhard 

Rationality cannot be restricted to the 

following of logical rules. Such a restriction 

encounters foundational problems - for 

example, What is the rational warrant for 

those rules? And it also encounters the 

following conundrum: No logic can construct 

a more powerful logic than itself. Therefore, 

if rationality is equivalent to honoring the 

rules of logic, the history of logic (and 

mathematics), which consists, among other 

things, of the construction of more and more 

powerful logics, is arational. 

I propose that the core of thought is not 

rationality, opposed by the creative passions. 

Instead, thought is fundamentally an internal 

variation and selection process, an 

evolutionary epistemology, involving 

creativity at its core. But a crucial aspect of 

the development of this process is the learning 

of selection criteria, of what constitutes error. 

Of course, such negative knowledge of error 

can itself be in error, so criteria of potential 

error form a hierarchy, with some criteria 

applying to constructions concerning 

interactions with the world, and other criteria 

applying to lower level criteria. Because such 

criteria, when expressed in words, form the 

grounds for criticism, I call them critical 

principles. 

The positive knowledge that is 

generally identified as rational is the 

knowledge of how to avoid error. Rationality, 

then, is a natural developmental tendency of 

this variation and selection creative process. 

One very general, and therefore important, 

kind of rationality focuses on relations among 

extensions of representations, independent of 

the specific natures of the elements in those 

extensions. For example, if the extension of A 

is included in the extension of B, then All As 

are Bs. This view yields a reconstruction of 

logic along the lines of Tarski, Mostowski, 

and Sher, and, thus, a recovery of logic as an 

aspect of rationality, though not its center, and 

rationality an aspect of creative variation and 

selection processes. Rationality and 

creativity, therefore, constitute aspects of an 

integrated developmental tendency, not 

opposing forces. The key to this integration is 

the negative knowledge of critical principles. 
Agent and Multi-Entity Systems Modeling 

C. Hein, H. Zebrowitz 

Abstract 

This paper describes a method for studying the functional and temporal performance of systems 

controlled by distributed autonomous agents through simulation of the agents within larger 

systems. 

There are many challenges to developing successful agent systems. Although there are multiple 

agent architectures or approaches for a given application, it is difficult to predict which is best. 

The behavior of complex distributed autonomous agent communities is notoriously difficult to 

predict or certify prior to the final implementation of an approach. Agent architecture 

development is quickly burdened with implementation details before major questions are 

answered, such as: 

 - stability, - convergence, - negotiation logic 

 - efficiency, - robustness, - agent architecture 

 - speed, - resilience, - agent class structure 

New capabilities are needed to predict and analyze agent architectures early, prior-to and 

throughout detailed development. It will assist in guiding optimization, and simplification of 

implementations. It can provide quick "what-if" analysis. 

A comprehensive, flexible agent modeling technique is needed which must model the outer 

systems that agents operate within, and which must resolve functional, temporal, and spatial 

aspects. Ideally, there should be an automated flow from modeling and development to fielded 

systems. Such capability would Support early demonstration, to incorporate feedback from users 

within time to accept it. 

A brief survey of previous agent simulation environments is presented, covering such tools as U. 

New Mexico - SWARM, and Brookings Institute/Nutech - Ascape, U. Chicago - Repast. 

Finally, an initial experimental model with two scenarios is described to add some concreteness 

to the discussion by example. A hierarchical agent-based simulation environment called ATLCSIMis introduced. The modeling work done with this tool demonstrates agent operations within 

larger systems while revealing timing performance/response and assessing functional quality of 

the collective agent solutions. The preliminary results show emergent multiple-level hierarchical 

organization. The first scenario involves agent navigation in a two dimensional space with a 

series of progressive challenges provided by a mixture of agent roles. The second scenario 

operates in a text-based mathematical equation space for a non-linear dynamic system. The two 

distinctly differing scenarios were chosen to demonstrate the generality of the approach, and to 

show that it can be applied to many domains. The work is contrasted with the previous efforts. 

References: 

[1] R. Pfeifer, C. Scheier, "Understanding Intelligence", 

 MIT Press, 1999, ISBN 0-262-16181-8. 
On Knowledge Representation issues 

Alex Abramovich 

webdao@yahoo.com 

ABSTRACT 

Knowledge Representations issues take on special 

significance in the light of development of the novel 

Web’s reality that involves the Semantic Web, GRID, P2P 

and other today’s ITs. In contrast to the previous IT 

evolution’s stages, the recent one utilizes ontology as 

separated resource. An elaborate knowledge 

representation approach implies an efficiency of 

knowledge-based systems and their interoperability. This 

paper deals with Ontology Engineering approach that 

allows both build and generate the consistent dynamic 

autonomous knowledge-based systems. 

Keywords: Knowledge Representations (KR), reasoning, 

human activity, domain world, private world, ontology

1. Introduction 

Range of Knowledge Representations’ issues, 

include, but are not limited to: 

1. measure of KR approach’s adequacy to the 

represented knowledge 

2. measure of knowledge role with respect to 

the goal that is trying to be achieved 

3. measure of overall quality of knowledge 

within the knowledge representation 

4. measure of knowledge uncertainty for the 

knowledge utilization by the autonomous 

system 

5. measure of the consistency of knowledge 

that is provided by the autonomous 

software agents or by the service providers 

6. measure of the ontologies’ role in 

autonomous systems 

Proceeding from the assumption that human 

behavior is defined by his knowledge, we have a 

right to expect a successful evolution of autonomous 

systems only under the stipulation that it exists a 

reliable KR foundation. 

Unfortunately, underdetermined system of KR’s 

terminology itself produces numerous problematical 

KR approaches.

In this paper we will attempt to look at aforesaid KR 

issues as at reasoning’s problems and to subordinate 

knowledge representation to reasoning one. 

1.1 What do we mean by knowledge 

In order to assess which types of knowledge 

representation are appropriate for which type of 

information, including corresponding performance 

measures as well as to consider other KR issues, it is 

necessary to define what we mean by knowledge. 

Consider some knowledge definitions from Google: 

The act or state of knowing; clear perception of fact, 

truth, or duty; certain apprehension; familiar 

cognizance; cognition. 

 "Knowledge, which is the highest degree of the 

speculative faculties, consists in the perception of 

the truth of affirmative or negative propositions." 

Locke.

That which is or may be known; the object of an act 

of knowing; cognition; -- chiefly used in the plural. 

"There is a great difference in the delivery of the 

mathematics, which are the most abstracted of 

knowledges." Bacon. "Knowledges is a term in 

frequent use by Bacon, and, though now obsolete, 

should be revived, as without it we are compelled to 

borrow "cognitions" to express its import." Sir W. 

Hamilton. "To use a word of Bacon's, now 

unfortunately obsolete, we must determine the 

relative value of knowledges." H. Spencer.

“That familiarity which is gained by actual 

experience; practical skill; as, a knowledge of life. 

"Shipmen that had knowledge of the sea." 1 Kings 

ix. 27.”

As we see, knowledge is one of those concepts, 

concerning which everybody has own opinion. 

Nevertheless, the last one seems the most operable. 

Practically, it equates knowledge with an activity 

representation. In any case, (since the practical skills 

is used by human in his activity) it means that 

knowledge is a mental instrument, with is used for 

the human activity achievement. 

Thus it is possible to say that knowledge is an 

instrument of reasoning. 

1.2 Why does a human think? 

Before we will define the reasoning model, it is 

appropriate to put a question – Why does a human 

think? 

“Reasoning is a mediate generalized reflecion of 

appreciable and regular dependences of reality.”[1] 

As such it is an instrument of human life cycle 

providing. 

“Thinking and acting are the specific human 

features of man. They are peculiar to all human 

beings. They are, beyond membership in the 

zoological species homo sapiens, the characteristic 

mark of man as man.”[2] 
Since a human life cycle is constituted by set of 

profession/living activities, reasoning serves these 

activities’ achievement. 

At that, knowledge is used as the human activities 

awareness. 

To Ludwig Edler von Mises [2] “human activity is a 

goal-seeking behavior” and “human action is 

necessarily always rational”. 

And so by human activity we mean: 

 Definition 1. Human activity is time-, place-, state-

, and event- ordered set of multidisciplinary actions 

aimed to achievement of socio-specified goal. 

1.3 Activities’ types 

In spite of the obvious differences of social 

institutions and persons, their life cycle as set of 

activities, on closer examination, seems in the 

following way: 

- An activity (activities) that provides the 

means of subsistence (both profession and 

other socially specified activities), 

- Properly living activities, namely, learning, 

execution, repair, protection, an 

advancement of results, supply, an analysis 

and control. 

The first activity (activities) belongs to certain area 

(areas) of expertise (domain). As domain activities 

we differentiate domain generic activities and 

private activities.

The properly living activities we designated by the 

common name of generic living activities.

Domain generic activity is a basis framework of 

actions, operations and/or activities aimed to 

achieve one or more domain specific goals, where 

domain goal is a socio-claimed product or service. 

Private activity is an adapted domain/living generic 

activity provided by a social unit, where by a social 

unit we mean a government, an enterprise, a 

community and a person. 

Thus we differentiate the following activity’s types: 

generic living activities, domain generic activities, 

and private activities. 

1.4 A human mental activity 

Now, there is time for correlate with each other a 

social unit’s life cycle, activities, knowledge and 

reasoning: 

 Definition 2. Reasoning is a human mental activity 

that operates with human activities knowledge for 

the purpose of the social unit’s life cycle providing. 

At that, on the level of the social unit’s life cycle 

organization reasoning operates with activities as 

with data type, and on the level of the activities’ 

implementation it operates with an activity’s 

components (see below) as with data types. 

It is important to note that reasoning trace is a 

certain algorithm, and its data types’ names 

constitute a reasoning ontology.

We differentiate life cycle of domain (domain 

world) and life cycle of a social unit (private world). 

Reasoning’s algorithm of domain world we 

denominate as domain world activity, and, 

analogously, reasoning’s algorithm of private world 

we denominate as private world activity. 

We emphasize the domain world activity and the 

private world activity, since, as a matter of fact, they 

define behavioral/management models of domain or 

of a social unit. 

 Definition 3. 

a) Domain world activity (Adw) is a resultant 

activity of the domain community, 

composed of domain generic activities 

(owned by domain experts) and private 

activities (owned by the other domain 

community’s members), aimed to the 

domain life cycle providing; 

b) Private world activity (Apw) is a resultant 

activity of the private profession/living 

activities, owned by social unit and aimed 

to the private life cycle providing. 

2. THE Reasoning 

The suggested Ontology Engineering approach 

forms a core of THE (Total Human Experience) 

Web project. In the network of THE Web project it 

is proposed to build an integrated Web knowledge 

resource (THE KB) with the purpose of the 

exhaustive Web service providing of the 

profession/living activities. THE Web service will 

be realized by an integrated multi-agent system 

(THE MAS) under multilevel dispatching. 

THE KB is constituted by human activities’ 

representation and derived ontological as well as 

causal environment. 

Human Activity is represented in form of Activity 

Proposition (AP) on the Reasoning Language (RL). 

RL is THE Web’s internal language that data types 

are represented by Core Ontology (CO), Domain 

Ontology (DO) (as CO extension), Private activity’s 

ontology (PO) as a certain DO extension, Domain 

World Activity’s Ontology (DWO) as DO 

extension, Private World Activity’s Ontology 

(PWO) as CO and a certain DOs extension that are 

derived from corresponding activities’ propositions 

(see below). 

AP represents an algorithm of the activity 

performance’ steady states transformation. So called 

Steady Reasoning (SR) serves (validates and directs) 

this algorithm performance. SR operates the 

following knowledge types: 

- A private activity’s initial state (AIS) 

- A state transforming private activity (STA) 
- Set of possible STA effect states as result of 

STA, 

where a state knowledge includes 

- a state ontology, 

- a state determinant, 

- determinants of state’s components; 

and a private activity knowledge includes 

- an activity ontology, 

- an activity’s states, 

- an instrumental private activities toolkit 

and 

- an activity’s determinant. 

At that, an activity’s and activity state’s determinant 

is a semantic framework of its ontology’s 

components that is a mandatory for inheritance at all 

generations. 

RL provides also transient reasoning’s means for the 

purpose of Transient Reasoning (TR) achievement. 

In addition to above mentioned, TR operates the 

following knowledge types, derived from THE KB: 

- Network of generalized causalities, 

- Generalized cause (that is, set of causes 

that derive from the same state the same 

effect), 

- Causality determinant. 

RL is interpreted by THE MAS reasoning 

framework (THE Reasoning). 

THE Reasoning process is provided by the 

following agents: 

1. Recognizer that recognizes determinants of 

activities and activities’ components,

2. Executor that executes the AP’s sequence 

of operations,

3. Predictor that predicts an eventual course 

of events,

4. Reason _detector that detects a reason of 

deviation from the specified steady state 

and generates a target setting,

5. Activity_generator that derives from the 

KB a new activity proposition as a 

discovered (or received) problem solving.

3. Activity Proposition

This paper is not RL presentation. Therefore we will 

consider RL features that concern Knowledge 

Representations issues only. RL is a procedural, a 

markup, an ontology language as well as an action 

language, destined for the description of reasoning 

that required for the activities’ performance. 

As a procedural language it allows to describe an 

activity’s algorithm. 

As an action language it represents a causality in the 

form of a triplet {I,C,E}, where I is an initial 

condition, C is a cause, E is an effect. 

As an ontology language it allows to input both 

concepts and concepts’ relations. 

As a markup language it provides a semantic 

marking of AP text that allows the ontology 

mapping. 

Activity Proposition plays a part of a canned 

program and at the same time it is considered as 

knowledge module. At once on completion of AP 

design, it occupies THE KB position in compliance 

with its causal interpretation. 

At that, it is necessary to note that we extend

concept of an activity actor beyond the social units. 

We mean by Activity Proposition (AP) a 

semantically marked description of purposeful 

system of operations that producible by human(s) 

and/or by service provider(s) and/or by 

apparatus(es) and /or by software applications.

 At that, 

- Activity’s ontology is AP text’s remainder 

of deletion both RL’s terms and lexical 

forms as well as semantic tags (that is, a 

semantic ordered set of words (ontology 

units) used for AP representation). 

- Ontology unit’s semantics is fixed by the 

nearest semantic tags (opening and closing) 

and 

- Ontology unit’s meaning is Web, THE Web 

or private resource. 

3.1. Personal world 

Private world (PW) is constituted by set of actual 

private profession/living (p/l) activities derived from 

Basis and Domain generic activities. At that, ever it 

remains the PW composition, namely, learning,

practice (that is, an execution of a socially specified 

activity(ies) that provide(s) the livelihood), repair, 

protection, an advancement of results, supply, an 

analysis and management. 

Every p/l activity is correlated with others by time, 

by place, by preferences and by cost. Space of 

correlated p/l activities is rank-ordered by APpw 

that represents a scenario of parallel/sequential 

executable private p/l activities, which are marked 

by a special set of tags. RL keeps AP special sets of 

semantic tags that define an activity’s position in the 

personal world. APpw provides a semantic sharing 

of private p/l activities as well as of private p/l 

ontology. Private world’s activity represented by 

APpw is aimed to the achievement of it’s owner p/l 

goals with a cost minimization. 

A priority of APpw’s performance produces a 

particular causal stipulation of private activities as 

well as particular reasons of response to external 

occurrences (a private logic). A corresponding 

APpw ontology has, therefore, private semantic 

features.

A private logic induces interoperability issues both 

on the profession and on the living level that must 

be considered as an operation problems both of PW 

management and of PWs interaction. In case that a 
response to an external occurrence is not contradict 

APpw performance’s logic it will be executed. If 

not, a response’s execution will hurt the PW. 

The response’s motivation takes on special 

significance for reasoning, particularly, for Reason 

_detector and Activity_generator. 

3.2 Domain world 

Domain world (DW) is constituted both by domain 

generative activities and by private activities of 

professional communities, of enterprises and of 

specialists. THE Web engine keeps AP special sets 

semantic tags that define a profession position of all 

domain world participants. A corresponding domain 

world AP (APdw) provides a semantic sharing of 

domain activities as well as of domain ontology. 

Domain world activity, represented by APdw, is 

aimed to the achievement of domain socioeconomic, 

sociopolitical and socio-productive goals with cost 

minimization. APdw performance is achieved via 

domain Web portal. 

3.3. THE self-organization 

Ontology constitutes the external level of human 

experience’s knowledge representation. Every Ontounit has THE KB’s multi-semantic position 

represented by set of DW related triplets 

(APdwName, APName, SemanticTag) as well as by 

PW related triplets (APpw, APName, SemanticTag). 

At that every Onto-unitName is accomponied by 

links to DOName or CO (that is, to Onto-unit 

parent’s name). 

This Ontology organization grounds an opportunity 

of the interoperability issues’ solving. 

Recognition of an activity’s determinant in the 

current input activates THE Reasoning process. 

3.3.1 Target setting’s processing 

A target setting as an output of Reason_detector or 

due to a customer’s initiative is sent to 

Activity_generator in form of an initial and a finite 

state. 

Using knowledge of activities states’ determinants, 

Activity_generator search the corresponding THE 

KB nodes and AP paths between them. 

The next problem is a correction of one of this paths 

with the purpose of utilization it by PW owner. 

This correction is a type of a semantic translation 

that represents a sequential revision of the intertags’ spaces. 

An impossibility of the inter-tags’ spaces filling is 

fixed as a problem that involves a target setting for 

Activity_generator. 

As result of this recursive procedure is a new AP. 

4. Measure of KR approach’s adequacy 

to the represented knowledge 

Suggested Ontology Engineering approach deals 

with unified model of above mentioned knowledge 

types (see paragraph “THE Reasoning”) 

representation. AP representations of existing 

software tools/agents/applications utilization’s 

procedures will extend THE KB. Representations 

ones will be used as procedures of access to these 

resources. In the same way it represented an 

implement’s, an apparatus’, equipment’s, a sensor’s 

(and so on) utilization as an activity states’ 

components representations. At that, principles of 

operation of above-named devices are represented 

by means APs too. 

Thus THE Web operates with active knowledge 

forms, for which AP representation is adequately. 

5. Measure of knowledge role with 

respect to the goal that is trying to be 

achieved 

According to M. Polanyi [3], the components of an 

optimally organized system must not be further 

partible in the certain, defined for this system, ratio. 

M. Polanyi made out of a system’s components at a 

ratio of their contributions to the goal achievement. 

A component’s position in the system’s organization 

defines its semantics. Its contribution defines the 

component’s significance. 

Due to RL notation, semantic tags define an 

ontology unit’s contribution to the AP, and an 

ontology unit is utilized as a pointer of a related 

resource that details an access procedure (or this 

knowledge principle of operation). Thus THE KB 

represents knowledge system, ordered in M.Polanyi 

sense, and THE KR approach provides a 

contribution of every knowledge unit to the goal’s 

achievement. 

6. Measure of overall quality of 

knowledge within the knowledge 

representation 

Since an ontological design is provided by domain 

expert or by APpw owner, the overall quality of 

knowledge within the knowledge representation is 

depended on its author’s skill level or on the APpw 

owner’s preferences that always may be submit for 

consideration of new customer. THE engine 

provides the AP designers’ rating and chooses (in 

the presence of choice) the best AP version. 
7. The ontologies’ role in autonomous 

systems 

Among a manifold of an ontology definitions the 

Protégé' one is the most close to RL notation: 

“Ontologies are explicit specifications of the types 

of resources that exist and possible relationships 

between them, and specific instances of concepts in 

the ontologies” (http://protege.stanford.edu/). 

THE Reasoning utilizes an ontology as a 

semantically ordered set of Web resources’ pointers. 

Similarly, a human operates on concepts. At that, as 

concepts it is used both scientific/technical/common 

terms and arbitrary identifiers of arbitrary objects 

sets as well as of various process’ parts, of states, of 

situations and so on. 

Therefore in THE notation the problem of primary 

importance is a reconstruction of the individual 

conceptual system (that is, the private ontology 

mining). A discovery of corresponding DO/CO 

terms grounds a semantic translation of private 

situation to the DO/CO specification. Only after 

that it is possible generating for customer a 

personalized Web service. Remind that in the 

previous chapters we considered an ontology as data 

type names’ space. Thus, since reasoning process is 

grounded by conceptual schemes, an ontology plays 

a part of primary importance for all knowledge 

based systems include autonomous ones. 

8. Conclusion 

We considered a particular Knowledge 

Representations’ approach. We simplified a problem 

by consideration unified KR form called Activity 

Proposition. We consider that it optimally satisfies 

both human and machinable reasoning and that in 

such a way we are able to build of a personalized 

Web service. 

Reference: 

[1] “Reasoning is a mediate generalized reflecion of 

appreciable and regular dependences of reality.” 

(http://azps.ru/articles/proc/proc9.html) 

[2] Ludwig Edler von Mises, “Human Action: A 

Treatise on Economics”,The Foundation for 

Economic Education, Inc. Fourth revised ed., 1996, 

printed 1998 

[3] M. Polanyi, Personal Knowledge, Harper & 

Row, New York, 1958