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B MBS TECHNICAL NOTE 940

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

The Representation and Use of Design Specifications

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'the primary communications and control tools

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.977
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and

technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to pro- mote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, the Office for Information Programs, and the

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THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consist- ent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of the Office of Measurement Services, and the following center and divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center for Radiation Research — Laboratory Astrophysics 2 — Cryogenics 2 — Electromagnetics 2 — Time and Frequency".

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languages. The Institute consist of the following divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE OF EXPERIMENTAL TECHNOLOGY INCENTIVES PROGRAM seeks to affect public policy and process

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1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Located at Boulder, Colorado 80302.
LIMUJiX

JUN 3 1977

/i^-/- ace.

The Representation and Use of

Design Specifications

^

s

6^5753

S.J. Fenves

University Professor

Carnegie-Mellon University

Pittsburgh, Pennsylvania

and

R.N. Wright, Director

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Also published in Structural and Geotechnical Mechanics, a Volume honoring Nathan M. Newmark, Editor William J. Hall, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1977

X** °P

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U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

US NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued June 1977
National Bureau of Standards Technical Note 940

Nat. Bur. Stand. (U.S.), Tech. Note 940, 51 pages (June 1977) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $2

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•it U.S. GOVERNMENT PRINTING OFFICE : 1977 O—240-870
TABLE OF CONTENTS

Page

ABSTRACT 1

1. INTRODUCTION 2

2. BACKGROUND 6

3. ANALYSIS OF SPECIFICATIONS ... 9

3.1 Development 9

3.2 Representation 11

3.3 Analysis 17

4. NETWORK REPRESENTATION OF SPECIFICATIONS 21

5. SYNTHESIS OF SPECIFICATIONS, 24

5.1 Formulation 24

5.2 Expression 26

6. USE OF SPECIFICATIONS 31

6.1 Extensions of Representation • 31

6.2 Computer Aids for Constraint Processing 33

7. SUMMARY AND CONCLUSIONS 37

ACKNOWLEDGMENTS 43

REFERENCES 44

TABLES

Table 1 Allowable Tension Stress n

Table 2 Slenderness Ratio Criterion 12

Table 3 Allowable Compressive Stress 13

Table 4 Stress Criterion for Tension Member 1^

Table 5 Conformance Criteria for Tension Member u^

Table 6 Conformance Criteria for Tension Member (modified) .... ig

Table 7 Classification of AISC Criteria 20

111
Page

FIGURES

Figure 1 Information Network for Allowable Stress and

Slenderness Ratio Criteria 39

Figure 2 Schematic Information Network for Tension and

Compression Member Criteria 40

Figure 3 Argument Trees 41

Figure 4 Decision Tree for Maximum Slenderness Ratio Criterion . . 42

IV
THE REPRESENTATION AND USE OF DESIGN SPECIFICATIONS *

by

S. J. Fenves and R. N. Wright

Abstract

Design specifications are presented as the primary communication and control

tool for the design and construction industry. Requisite properties of

completeness, uniqueness and correctness are identified, and the role of

performance and limit state concepts in specifying intent of the specifications are emphasized. Formal representational methods are presented at three

levels: decision tables for specification provisions, an information network

for related provisions, and argument trees for organizing and outlining. An

idealized process for specification development is presented, and the use of

the representational tools for checking specifications and providing strategies for textual expression is described and illustrated. Development of

computer aids for specification processing in design and conformance checking

is described.

Key words: Building codes; computer programming; decision tables; graph

theory; performance specifications; standards.

Note this report was prepared for presentation at the Symposium on Structural

and Geotechnical Mechanics, University of Illinois, Urbana, Illinois,

October 2-3, 1975.

*Also published in Structural and Geotechnical Mechanics , a volume honoring

Nathan M. Newmark, editor William J. Hall, Prentice-Hall, Inc., Englewood

Cliffs, New Jersey, 1977
1. INTRODUCTION

We use the term design specifications to encompass all types of formal

documents used for the evaluation of engineering or architectural

design. These include:

o legal building codes;

o model building codes;

o consensus standards such as the ACI Building Code Requirements

for Reinforced Concrete (2) ;—

o proprietary or trade association specifications such as the

AISC Specification for the Design, Fabrication and Erection of

Structural Steel for Buildings (20) ; and

o specifications of agencies or owners, such as the U.S.

Department of Housing and Urban Development Minimum Property

Standards for Federal Housing Administration mortgages (10)

.

Our discussion specifically excludes project specifications and other

specifications used in contractural relationships, and product specifications describing existing products or systems.

Design specifications are the primary communication tools and control

mechanisms for the design and construction industry. They provide for

effective expression of intent between owners, designers, public authorities, builders, and users of buildings. The quality of the built

-Numerals in parentheses refer to entries in the Reference,

2
environment, including its functionality and safety, is directly depenent on the quality of the specifications controlling its design.

Ventre (21) has argued that because of the "diverse, dispersed, detached,

and discontinuous" nature of the building industry, specifications, and

especially their legal embodiments in building codes, represent essentially the only "collective memory" of the industry.

Design specifications represent the culmination of a broad professional

concern. Generally, design specifications intend to assure the functionality of a building or system and to protect the public health, safety

and welfare during construction and use. Designers and building regulatory officials use design specifications to achieve a common understanding in order to effectively control designs. Specification writers

translate knowledge of the environment, structural behavior, and

requirements for functionality and safety into usable requirements or

practices in specification form. Most civil engineering researchers aim

to improve design and construction practices; much of the output of this

research is implemented through new or revised specifications. Siess

(19) has described the mutual interaction and reinforcement between

research, practice and specifications.

While most researchers are concerned with improving the content of

specifications by basing them on more rational models of material and

structural behavior, our concern is primarily with the format of

specifications. It will be shown that the two aspects of content and

format are closely interrelated, and that methods designed to improve

their format can also yield better content.

3
At the present, there are no recognized formal methods for generating or

reviewing proposed new specifications or modifications of existing ones.

Notwithstanding the importance of design specifications to the building

industry and the cost of producing them, there is no methodology, beyond

informal peer review and occasional test comparisons with previous

specifications, for making any quantitative evaluation of proposed

specifications. Furthermore, while an increasing fraction of processing

of design information against specifications is performed by computer

programs, the entire responsibility for the correctness of these programs,

including the selection of provisions to be included and the detailed

interpretation of these provisions, rests with the computer program

developers. Neither the users of these programs nor building officials

required to pass judgment on their output have any ready means to

ascertain that programs perform in all cases as intended by the

specification writers.

We will show here that rigorous mathematical foundations exist on which

efficient, formalized procedures for developing and using specifications

may be built. These methods apply to three distinct processes:

o formulation , the development of the information content of the

specification;

o expression , the exposition of the information content in both

conventional textual form and in forms adaptable for computer

processing; and

o use , the interpretation and application of the specification

to the evaluation of designs in both manual and computer-aided

processes.
Our objective is to improve engineering practices through better

specifications and better methods for their use. We present the bases

for a systematic approach to the formulation, expression, and use of

specifications which assure three requisite properties:

o completeness , that the specification explicitly applies in any

possible situation;

o uniqueness , that the specification yields one and only one

result in any possible situation; and

o correctness , that the result is that intended by the

specification writers.

The methods presented are suitable for both manual and computer-aided

applications by specification writers, designers, and reviewers for

building regulatory authorities. With slight modifications, the methods

are equally applicable to three types of design specifications:

o performance specifications , which state the required attributes

in a scheme- independent manner, such as the Guide Criteria for

Operation BREAKTHROUGH (9)

;

o procedural specifications , which state required attributes and

procedures for their evaluation in a scheme -dependent manner,

such as the ACI and AISC specifications; and

o prescriptive specifications , which state required dimensions

or properties in a manner completely defining the acceptable

configurations or procedures in a scheme -dependent manner,

such as the One and Two Family Dwelling Code (6)

.
2. BACKGROUND

The investigation of the properties of completeness and uniqueness of

specification provisions is closely related to the aspect of linguistics

called syntax , dealing with language organization. Correctness, on the

other hand, deals with meaning and intent, and is therefore related to

semantics . The formalization of the semantic aspect of specifications

is aided by two powerful concepts.

First, the performance concept involves stating the attribute satisfying

the needs of the users without prescribing the materials, components, or

systems to be employed. J.R. Wright (22) describes the evolution of

the performance concept from its apparent beginnings at the Building

Research Station in the United Kingdom in the 1930' s. As will be shown,

performance is important for all specifications, not only performance

specifications, since it gives explicit attention to the attributes the

designer intends to provide.

The limit state concept is a second formalism appropriate to the semantics

of specifications. As described by Allen (1), limit states describe

those conditions for which systems or elements would no longer fit their

intended purposes. A limit state is not synonymous with a performance

attribute, since the condition may deal with a response related to the

intended performance, such as cracking, but not occurring in all possible

solution schemes.
Neither the performance attributes of interest nor the limit states of

concern are explicitly expressed in most existing specifications. This

lack of clarity has made it difficult to improve specifications through

research, as there can be no certainty that a specification provision is

improved if neither the response of concern nor the desired performance

attribute is clearly defined.

The proper syntax or organization of the information in specifications

is also vital to the transmittal of intent from writers to the users.

Frequent complaints of practitioners and students alike indicate that

specifications are "too complex" and "hard to follow." It will be shown

that many of these valid complaints can be removed by the use of formal

methods to assure that the intent of the specification writers is

maintained in the textual expression.

The methods here are primarily based on the writers' cooperative efforts

over a long period. In 1966, Fenves (5) identified the applicability of

decision tables, a then-recent program development tool, to the representation of provisions of procedural design specifications. With

Gaylord and Goel, he presented in decision table form the AISC Specification (7) . Decision table formulations of other design specifications

have been developed by Seeberg (18) and Noland (12)

.

The AISC study (7) also revealed that the information content of the

specification is topologically related in a hierarchical network; this

observation led to a prototype computer program for the review of

7
designs (8). Wright, Boyer and Melin [23) recognized that the topological

relationship of data provided a key to the efficient formulation and

processing of constraints in computer-aided design programs. The

implication of these studies on computer-aided design was summarized by

Fenves (7) . Fenves and Wright investigated the application of the

concepts developed to the restructuring of the textual expression of the

AISC Specification (24, 15). Based on this work, Nyman and Fenves (14)

explored algorithms and computer aids for organizing the information

content of specifications and its textual expression. The methodology

has been advanced substantially in work continuing at Carnegie-Mellon

University, the National Bureau of Standards, and the University of

Illinois. This paper summarizes the technologies and presents the

recent advances.
3. ANALYSIS OF SPECIFICATIONS

The concepts outlined in the preceding sections are best illustrated by

applying them to the analysis of selected portions of the AISC Specification (20) . The AISC Specification, as most specifications in use

today, is an outgrowth of a long historical development started decades

before the concepts of performance and limit states were introduced.

Thus, a part of the analysis is to locate and identify these qualities.

3.1 DEVELOPMENT

In performance terminology, the AISC Specification deals with the entity

"structure" or "structural system" and the two major attribute categories

of "safety" and "serviceability." Within "safety," the environment of

concern is the effect of external loads, while for "serviceability," the

concern is with fitness for erection and use. To achieve these performance attributes, the design must guard against applicable limit states.

The entity "structure" must be further subdivided. A major category is

that of "member," which is readily distinguished from other categories,

such as "connection" and "connector," dealt with in the Specification.

The entity "member," however, is still too general, in that specific

limit states cannot be directly associated with it. Since limit states

are related to response, it is convenient to introduce a subdivision of

members by stress type, such as "tension," "compression," etc. It is to

be noted that stress type is not a strict subdivision of members (at
different stages of the design process, a member may be investigated for

different stress types or combinations) , but a common property of members

which acts as a selector to associate members with the applicable limit

states.

For the subdivision of "tension members," the applicable limit states

under "safety" are "yielding" and "rupture," whereas under "serviceability,"

the AISC Commentary specifically mentions "undesirable lateral movement

("slapping" or vibration)" (4).

Finally, it is necessary to prescribe a measure which will insure satisfactory performance. In dealing with members, the AISC Specification

handles the safety attribute by specifying a maximum allowable stress,

and satisfies the serviceability attribute by limiting the slenderness

ratio.

Thus we arrive at the two provisions of the AISC Specification dealing

with tension members, reproduced verbatim from reference (3):

"1.5.1.1 Tension

On the net section, except at pin holes:

F = 0.60F

but not more than 0.5 times the minimum tensile strength of the steel.

On the net section at pin holes in eyebars, pin- connected

plates or built-up members:

F^ = 0.45F ."

t y

10
"1.8.4 Maximum Ratios

The slenderness ratio, 0>/r, of compression members shall not

exceed 200.

The slenderness ratio, KX/r, of tension members, other than

rods, preferably should not exceed:

For main members 240

For bracing and other secondary members .... 300."

3.2 REPRESENTATION

In this section we deal with the formal representation of specification

provisions and their relations, using as examples the provisions identified

above. Three representational tools are used, corresponding to three

levels of abstraction of specification.

Provision Level

At the level of single provision, the technique of decision logic tables,

or decision tables for short, is used. The decision table representation

of Section 1.5.1 is:

Table 1. Allowable Tension Stress

At pinhole N Y

F^ = min. (0.60F , 0.50F^ ) t y ts y Y

F+ = 0.45F

t y

Y

As can be seen, the table is divided into four sections. The upper left

section, called condition stub , is a list of all Boolean conditions (in

this case, the single condition "at pinhole?") . The lower left section,

11
called action stub , is a list of all applicable actions. The upper

right section, called condition entry , contains entries of Y (yes) or N

(no) corresponding to the conditions, organized into vertical columns

called rules . A particular rule governs if the given data (values of

the Boolean conditions) match the values given in that rule of the

condition entry. Finally, the lower right section, called action

entry , contains entries of Y and blank indicating that the corresponding

action is or is not to be executed in a given rule. The table is to be

read by proceeding down within a rule and across for each succeeding

rule as follows: "If not at pinhole, then F = min. (0.6F , 0.5F ); t y' ts 7

if at pinhole, then F = 0.45F ." For tables with more than one

*- y

condition, it is understood that the conditions are related by the

logical operator and .

Section 1.8.4 is represented by the following table:

Table 2. Slenderness Rat io Criterion

Compression member Y Y N N N N N N E

Member a rod I I Y N N N N N

Check for max. ratio desired Y Y I N Y Y Y Y

Main member I I I I Y Y N N

K£/r < 200 Y N I I I I I N*

K£/r < 240 y* I I I Y N I N*

0,/r 1 300 Y* I I I Y* I Y N

Section 1.8.4 satisfied Y Y Y Y Y

Section 1.8.4 not satisfied Y Y Y

Else action Y

12
Several new symbols may be noted in the condition entry. First, a

number of conditions is immaterial (I) in certain rules (e.g., the

question "main member?" is immaterial for compression members). Second

the symbols Y* and N* are introduced to denote implicit entries, that

is, entries known to be yes or no from other conditions (e.g., if "K£/r

_< 200" is true, it implies that "Kii/r £ 240" and "KX/r 1 300" are also

true) . Finally, the last column, denoted E for else , covers all possible

combinations not matched by the other rules; the corresponding action,

designated else action , indicates that there are combinations of conditions

not covered in the provision.

The decision table corresponding to Section 1. 5. 3- -Compressive stress is

shown below:

Table 3. Allowable Compressive Stress

Main member Y Y N* N* N* N* N* N*

Bracing or secondary members N* N* Y Y Y Y N* N*

Plate girder stiffener N* N* N* N* N* N* Y N*

Web of rolled shape N* N* N* N* N* N* N* Y

K£/r < C

c Y N Y N Y N I I

£/r < 120 I I Y Y N N I I

F by Eq. 1.5-1 Y Y

F by Eq. 1.5-2 Y Y

F by Eqs. 1.5-1, 1.5-3 Y

F by Eqs. 1.5-2, 1.5-3

cLS Y

F = 0.60F

a y

Y

F = 0.75F

a y

Y

13
The first four conditions are mutually exclusive, that is, a compression

member can only be one of the four types covered in the provision; thus,

in every rule, only one of the first four entries is yes, the other

three being implicit no's.

Each table generates only one item of data, which can be a numeric value,

such as F , or a Boolean datum, such as "Section 1.5.1 satisfied." This

restriction to a single output, absent from our early work (7), is

necessary for the proper interaction with the information network to be

discussed. The result generated in one table can be used in conditions

of other, higher- level tables:

Table 4. Stress Criterion for Tension Member

f < F

t - t

Y N

Section 1.5,1.1 satisfied Y

Section 1.5.1.1 not satisfied Y

Here, a single value of F is used, regardless of which rule of Table 1

generated it. Finally, all provisions for a tension member can be

combined in one table.

Table 5. Conformance Criteria for Tension Member

Section 1.5.1.1 satisfied

and

Section 1.8.4 satisfied

Y N

Tension member conforms Y

Tension member does not conform Y

14
In this table, a compound condition is used to indicate that both the

stress and maximum slenderness ratio criteria must be satisfied for the

member to be acceptable.

Information Network

At the next level of representation, we are concerned with the information

flow between related provisions, specifically, the manner in which data

generated or defined in one provision are used in other provisions in

order to represent the hierarchical sequences of definitions, computations

and tests comprising the specification.

The logical relations between items of data are described by two relationships,

that of ingredience and dependence . The ingredients of an item are all

data items needed to evaluate that item. Referring to Table 1, the

ingredients of F are: F , F and the Boolean variable "at pinhole."

Conversely, the dependents of an item are all data items which are a

function of the data item in question.

A convenient representational tool for these interrelations is a directed

graph or information network , obtained by assigning a node to each data

item and assigning a directed branch from the data node to each of its

dependents. Since, as discussed earlier, each decision table produces

only one data item, it is not necessary to distinguish in the graph

between nodes generated by a formula or by a decision table.

15
A somewhat condensed information network for the three provisions

discussed above is shown in figure 1. More detailed networks, which

include the intermediate computations and tests within a provision, are

given in (13). Larger networks, including the global network of an

entire specification, can be built up from subnetworks, or, more precisely,

from the ingredients or dependents of the individual data items. As an

illustration, the network for tension and compression member criteria is

sketched in figure 2. The sketch is intended to illustrate that the

effective length factor, K, taken as a simple ingredient in figure 1, is

in fact, the terminal node of a subnetwork, and that the evaluation of

the members also requires computation of the actual stresses f and f ,

involving definitions of net and gross areas, and the like, and checking

of Section 1.9 for limiting proportions of column elements. The subnetworks

indicated by dashed lines intersect the network shown in figure 1.,

i.e., share some of their ingredients.

Organizational Level

Finally, at the topmost level of representation, our concern is with

identifying keywords or arguments which concisely describe the scope or

range of applicability of a provision, and their interrelationships,

which may be used to organize or outline the entire specification. These

arguments can be represented as hierarchically structured argument

trees . Figure 3a represents the segment of the attribute tree for the

physical component descriptions encountered in the AISC Specification

provisions discussed above. It is to be noted that a member may have

16
only one attribute at any one level (e.g., a member is either "main" or

"secondary"), but it may have attributes from several ievels.

3.3 ANALYSIS

Analysis for the three requisites of uniqueness, correctness and

completeness can be carried out at each of the three levels discussed

above. Furthermore, the analysis deals both with syntax, that is, "how

to do it?", and with semantics, that is, the "why?" for each provision,

group of provisions, or the entire specification.

Provision Level

Decision tables lend themselves directly to syntactic analysis for

uniqueness and completeness. Because the condition entry is a matrix of

Boolean variables, formal tests for uniqueness (lack of redundancy or

contradiction) and completeness are available (17). For example,

analysis of Table 2 shows that it is incomplete, in that it contains no

rules for which condition 1 ("compression member") is yes and condition 3

("check for maximum ratio desired") is no. However, a review of the

Specification and Commentary indicates that the table is functionally

complete since the limitation of KX/r £ 200 is mandatory, and not

optional as for tension members.

From a semantic standpoint, a major shortcoming of the present AISC

Specification is, as discussed before, the absence of explicit reference

to performance attributes and applicable limit states. Provisions for

17
tension members could, for example, be restructured according to the

decision table shown below, with appropriate measures identified for the

controlling limit states:

Table 6. Conformance Criteria for Tension Member (modified)

Stress concentration present N N Y Y

Yield criterion-, satisfied

and

Rupture criterion satisfied

and

Slenderness criterion satisfied

Y N I I

Yield criterion- satisfied I I Y N

Tension member conforms Y Y

Tension member does not conform Y Y

Information Network

At the information network level, the directed graph can again be used

for syntactic analysis. In particular, for completeness and uniqueness,

the graph must be:

o connected, that is, there can be no data items which are not

ingredients or dependents of other items; and

o acyclic, that is, there can be no closed directed paths in the

network, as this would imply either circular definitions or

iterative computations.

These two properties can be ascertained by standard network traversal

algorithms. The information network cannot be formally analyzed for

correctness and semantics. As will be shown in Section 5.2, a major

18
source of incorrect interpretation arises from the textual expression of

the network.

Organizational Level

At the organizational level, the directed tree of arguments is again

well suited for analyzing completeness and uniqueness, which require

that at each level the arguments be:

2/ o exhaustive, that is, cover all possibilities— ; and

o mutually exclusive, that is, a given element should match only

one argument.

In order to properly address the semantics of the specification, the

argument tree of physical component descriptions must be complemented by

a second, independent argument tree of performance attribute and limit

state descriptors, as shown in figure 3b. Each of the criteria can then

be uniquely identified by the applicable entries from the two argument

trees, as illustrated in Table 7.

27

' ' — In figure 3, dashed horizontal branches are used to indicate that the

arguments shown do not constitute an exhaustive set.

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4. NETWORK REPRESENTATION OF SPECIFICATIONS

In this section, the representational tools discussed in Section 3.2 in

connection with a segment of a specific specification are formally

summarized.

Provision Level

The logical content of a specification provision is represented by a

decision table. The decision table, in turn, can be converted to a

decision tree , which is a graph having the following properties:

o there is a single entry node with one exit branch;

o all intermediate nodes have one entering branch and two exit

branches, corresponding to the two outcomes (yes or no) of the

condition represented by the node; and

o terminal nodes have one entering branch and no exit branches,

and correspond to the rules of the decision table.

Each decision table produces one data item, the rules only identifying

alternate methods or formulae for deriving the item. A degenerate

decision table is a function, containing no conditions and represented

by a single node. A decision tree representation of Table 2 is shown in

figure 4. As discussed in Section 3.3, there is a terminal node

corresponding to the else rule. As can be seen from the figure, the

decision tree resembles a conventional flow diagram, and is thus

familiar to programmers. On the other hand, a decision tree always

implies a specific sequence of testing the conditions, whereas the table

is independent of sequence. The use of alternate sequences for different

textual expressions is discussed in Section 5.2.

21
Information Network

The hierarchical interrelationship among data items appearing in a

specification can be represented by two sets of compact lists, the

ingredience and dependence lists. Formally, for each data item d., the

ingredience list:

iCd.) - (d^, i . . .,<y

is the list of data items directly entering into the determination of

d-. Conversely, the dependence list :

D(d.) = {d , d ,...., d }

is the list of data items which directly depend on d-, i.e., for which

d. is an ingredient. These lists can be represented in graph or network

form by assigning a node to each datum and a branch from each datum to

all elements of its dependence lists. Global dependents of a datum can

be traced out by traversing the network from the datum in question to

all nodes reachable in the direction of the branches. Global ingredients

of a datum can be similarly located by traversing the network in the

direction opposite to that of the branches. Data items having no

ingredients are basic parameters which must be independently defined for

the written expression of the specification or input directly for

computer processing. Data items having no dependents are the criteria

which must be evaluated to ascertain conformance with the specification.

Organizational Level

Finally, for organizing, outlining, and indexing purposes, a number of

descriptors or arguments is associated with each criterion. The arguments

form argument trees, representing the logical subdivisions of the

22
organizational bases. In every specification, there are at least two

disjoint argument trees, corresponding to the subdivisions of the

physical entities addressed and the performance attributes sought,

respectively, as illustrated in figure 3. Additional argument trees may

be introduced where provisions deal with certain common properties which

do not strictly correspond to physical subdivisions or performance

attributes. Formally, for each criterion, the argument list :

ACdj) = {ak

, ar

. . . , am

>

is the list of all arguments applicable to the criterion. The. list

contains only the terminal argument from each attribute tree applicable

to the criterion; the path to that argument from the root of the tree is

uniquely determined by the requirement that arguments have unique names.

Conversely, for each argument, a, , the scope list :

S(a

k

) = {d

i5 &., . . ., d

Q

}

is the list of all criteria for which the argument appears. Table 7,

read row-wise, represents the argument sets of the 14 criteria shown;

read columnwise, it represents the scope list of each terminal argument.

23
5. SYNTHESIS OF SPECIFICATIONS

In synthesizing or developing a new design specification, many concurrent

activities of groups of professionals occur. Generally, it is not

possible to completely separate the contents of the proposed specification from its format, nor can one clearly distinguish the activities

of generating the information base of the specification and of writing

the text expressing this information. The development process is

frequently iterative, where new concepts, even the need for new research,

emerge as portions of the specification are developed. Nevertheless, it

is useful to postulate a simplified, linearized model of the synthesis

process, the first stage, formulation, dealing with the development of

the information content and the generation of its formal representation,

and the second stage, expression, dealing with the formatting of that

representation.

5.1 FORMULATION

A linearized model of the formulation process consists of five successive

activities. All specifications deal, explicitly or implicitly, with

performance objectives. Thus, as a first step, the performance attributes

to be achieved must be defined. Design specifications and building

codes have traditionally dealt with the overall objectives of maintaining

health and life safety; more recently, additional attributes, such as

energy conservation or operability after natural disasters, have been

introduced as requisites. An attribute such as "maintenance of life

2U
safety" is too broad a concept for developing specification provisions.

Therefore, the environments or factors within each attribute have to be

further isolated and identified. For example, "safety" may be subdivided

into "internal effects," such as explosions and other potential causes

of progressive collapse, and "external effects," such as wind, earthquake,

and the like. This leads to the identification of the anticipated

response of the system to the adverse environment, and to the definition

of the limit states, that is, the conditions under which the anticipated

response renders the structure or system unfit for its intended purpose.

As the second step, it becomes necessary to identify the physical

entities which are susceptible to failure or disfunction corresponding

to the limit states considered. As mentioned earlier, it is advantageous

at this stage to introduce common abstract properties, such as, "tension

stress" for certain ultimate limit states or "horizontal surfaces" for

the limit state of ponding, rather than attemption to exhaustively

enumerate all possible components or configurations susceptible to a

given limit state. The intersection of limit states, common properties

and physical elements identifies the criteria that have to be met.

The third step involves the definition of measures quantifying each

criterion, from simple statements that a certain device or item shall be

provided to limits or ranges on critical parameters. As a fourth step

in the formulation process, evaluation procedures must be developed to

ascertain each of the measures defined previously. In performance

25
specifications, these procedures are treated separately from the

criteria, whereas procedural specifications consist largely of the

detailed exposition of such procedures.

Throughout the formulation process outlined, the growing information

base of the specification being developed can be directly incorporated

into the formal representation. Specifically, the first step involves

the development of the attribute argument tree, such as the one given in

figure 3b. The second step consists essentially of the development of

the physical entity argument tree, the definition of criteria, and then

the establishment of the argument and scope lists. The third and fourth

steps involve the development of the information network among the

related criteria, measures and evaluation procedures and the generation

of the decision tables for the individual provisions.

The final step in the formulation process consists of the application of

the analysis tools described to the representation, in order to ascertain

the requisite properties of completeness, uniqueness and correctness. At

the risk of repetitiousness, we emphasize that such analyses will

inevitably reveal violations of the above properties and require additional

iterations on the formulation process.

5.2 EXPRESSION

We call expression the process of converting the abstract representation

into usable forms for a readable textual format and for the generation

of computer aids. This latter topic will be discussed in the next

chapter after some additional topics are introduced.

26
The difficulties of achieving a usable, readable text arise because the

text must follow a linear sequence, whereas the information it contains

is highly non- sequential, consisting of disjoint argument trees terminating

in criteria, which in turn depend on an information network with many

multiple connections, the nodes of which themselves may consist of

substantial decision trees. Expression is, therefore, the task of

unraveling this complex structure into a linear format that is easy and

convenient to use, that gives confidence to the designers that they are

following the specification writers' intent, and that similarly gives

assurance to the specification writers that the provisions are correctly

interpreted and executed.

We are convinced that many of the complaints concerning present specifications, and often the resistance to the introduction of new ones, are

the result of poor textual expression, as evidenced by awkward outlines

and uninformative provision headings, lack of proper cross-referencing

among related provisions, procedural sequences poorly related to the

design process, and badly composed provisions which are hard to interpret

and follow.

We are not in a position to propose universally applicable methods for

expression, but we have developed strategies which may be explored by

specification writers in order to achieve better textual expression, and

computer aids which allow exploring alternatives without the danger of

losing the intended coverage and meaning. These strategies are essentially

means for transforming the complex representation into different linear

sequences.

27
Provision Level

Here, the problem is that of converting a decision table into a decision

tree, which can then be expressed as one or more sentences containing

conditional clauses. The literature on decision table processing

discusses two basic strategies, called immediate decision , where the

objective is to isolate rules as quickly as possible, and delayed

decision , where the objective is to reduce the number of possible rules

roughly in half with each test (17) (the numerical analyst will recognize

the analogy of the two strategies to searching by iteration and searching

by interval halving , respectively) . These two strategies can be directly

applied to the expression of provisions: in the immediate decision

method, the simplest rules (containing the largest number of immaterials)

,

unique rules (differing in one condition from all other rules) , or the

most common rules could be listed prior to the other rules; in contrast,

by following the delayed decision method, provisions could by systematically

broken into shorter subprovisions of roughly equal scope.

Information Network

At the intermediate level, the problem is that of representing the graph

of the information network by a suitable spanning tree (i.e., a subgraph

which contains all the nodes of the original graph but only as many

branches as necessary to provide a single path from any node to any

other node) , and then to display the nodes of the tree in a linear

sequence. By the nature of the information network, all branches not in

the spanning tree become cross-references among the data items. Two

strategies for generating such a spanning tree are available, involving

28
a simple graph traversal algorithm. Assume that a fictitious "end" node

is made a dependent of all terminal (criterion) nodes, a fictitious

"start" node is made an ingredient of all input (basic parameter) nodes,

and that all branches are of "length" one. If the nodes are ordered by

increasing longest path from the "start" node, one obtains a sequence,

which we call direct execution , in which every term, formula, test, etc.

is defined just before it is first used, yielding concise, specific

sequential instructions, with all cross-references pointing to terms

previously defined. The strategy can, however, become lengthy and

tedious for an experienced user thoroughly familiar with the specification.

By contrast, if the nodes are ordered by increasing longest path from

the "end" node, one obtains a sequence, which we call conditional

execution , where the criterion to be checked is given first, followed by

its ingredient subcriteria, and so on, until finally the basic data

elements are defined. Such a strategy permits an experienced user to

read only as far down as necessary to locate the controlling provision

or test; however, if necessary, by reading further he can refresh his

memory on more detailed provisions. Variants of these two strategies

are further discussed in (15)

.

Organizational Level

In generating the outline and overall organization of the specification,

it is necessary to linearly sequence criteria which are indexed and only

partially ordered by the nodes of disjoint attribute trees, as illustrated

in Table 7. We have not yet developed general strategies for this phase

of expression. It is to be noted, however, that here syntax and

29
semantics interact very strongly: a sequencing which orders first on

attributes and limit states, with the physical classification in a

secondary rule, is likely to be more appealing to the researcher and

theoretically inclined designer, whereas the opposite strategy is likely

to be more familiar and convenient to the average designer.

The three sets of strategies discussed should be taken as boundary

values on a continuum of possible expressions, rather than as absolute

alternates. Any given specification is likely to contain a mixture of

all the above strategies. It is also possible that eventually frequently

used specifications may be expressed in one form for a specific use,

say, for designers, and that alternate forms may be provided for

alternate uses, say, one for students and another one for building

regulatory officials, with full confidence that the contents and meaning

will be preserved.

30
6. USE OF SPECIFICATIONS

In the Introduction, we refer to use as the application of specifications

to the evaluation of designs in both manual and computer-aided processes.

It is to be hoped that manual processing can be improved by the application

of the formulation and expression strategies discussed. Computer-aided

processing can also benefit significantly from the methods discussed, as

will be demonstrated in this section.

In computer-aided processing, one deals with constraints, rather than

criteria. A constraint is a particular application of a design criterion.

It is particular in the sense that it is a criterion applied to a

particular entity or point for a particular loading or environmental

condition. Usually, each design criterion results in many constraints.

Systematic approaches can be provided for the computer-aided development

of programs for constraint processing. These aids are significant

because manual programming is extremely expensive and subject to

mistakes in the interpretation of the intent of specifications. The

cost of preparation of new computer aids for constraint processing

appears to become a major impediment to the implementation of research

knowledge in improved specifications.

6.1 EXTENSIONS OF REPRESENTATION

In order to accommodate constraint processing, the representation

presented in Section 4 has to be extended in three ways.

31
First, in representing criteria, we treated a particular datum (e.g,

member length, I, stress, F etc.) as an individual item. In actual d

design use, these quantities would be subscripted variables (e.g., the

length of the ith member, the stress at station k of member i in loading

condition 1, etc.). All such subscripted variables are stored in some data structure which is accessed by the design and analysis routines as well as the constraint processor. The logical data of the specification

must be related to the subscripted data of the files for computer-aided

data processing. This relationship cannot be a fixed property of the

specification, since it should be possible to use the specification with

a variety of project data structures. Therefore, we have presented

elsewhere generalized procedures for generating constraint processors

compatible with rational, but essentially arbitrary, file structures

(23, 24). The significant feature of these procedures is that additional

ingredients, called pointer vectors , are appended to the ingredient

lists. A typical pointer vector would, for example, relate stations

along the member to the member designation. The extended representation

only shows that a pointer vector is needed to access the stations where

the stress constraint is to be checked; the actual form and content of

the vector would depend entirely on the data file structure for the

particular project.

Second, the ingredience and dependence relationships themselves must be

extended to account for the subscripted nature of the actual design

data. In the work cited (23, 24), we have developed a calculus of

subscript calculations, so that the subscripts of the dependents can be

automatically obtained from the subscripts of the ingredients, and

32
vice-versa. This approach can significantly decrease the cost of

developing computer aids for constraint processing.

Finally, in design, data also have a temporal character. In our early

work, we made use of the concept of status (8) . The status of a datum

is valid if it has been calculated in accord with the current values of

all the data in its global ingredients. The status of a datum is void

if it has not yet been calculated, or if changes have been made in one

or more of the items of data in its global ingredience since the datum

was computed. More recently we have introduced the concept of permanence

levels to distinguish between levels of definition of data (25) . For

instance: data being used by a number of different groups of the design

team, such as the architects, structural engineers, and mechanical

engineers, might be given a permanence level 1, data used in a more

transient fashion by one of these disciplines designated level 2. A

trial structural design might be conducted at level 3, the gradient

calculations used to determine whether an improvement in the design is

possible might be conducted at permanence level 4, and when the trial

design is determined to have converged its data might be relabeled to

level 2, when the structural design is deemed consistent with the

current work of the architects and mechanical engineers, it could be

relabeled at permanence level 1.

6.2. COMPUTER AIDS FOR CONSTRAINT PROCESSING

The computer aids available for efficient constraint processing can

again be discussed at the three levels used previously.

33
Provision Level

Two direct uses can be made of the decision table representation of

specification provisions. First, decision tables can be used directly

as a programming language; efficient preprocessors exist which convert

decision tables to procedural language statements using the strategies

discussed in Section 5.2, thereby significantly reducing programming

costs (17) . Alternatively, the decision tables can be used as data by a

general -purpose interpretive program (8) , thereby providing great

flexibility in experimenting with alternate specification provisions,

as only the data would have to be changed.

Second, wherever specification provision deals with several entities, or

allows designer choices or alternatives, and a particular organization

knows a priori which of these entities or choices it intends to use, the

application programs can be drastically reduced in size by the systematic

elimination of options not wanted. As an example, Table 2, introduced

previously, could be systematically reduced to the following programs:

o compression members only (one condition, two rules)

o all tension members (five conditions, six rules)

o tension members with slenderness check (five conditions, five

rules)

o tension members without check (table eliminated altogether)

.

Information Network

The two strategies, direct and conditional execution, discussed in

Section 5.2. are directly applicable to constraint processing. Conditional

execution begins with the particular constraint to be evaluated, tests

whether it can be evaluated directly from its ingredients, and proceeds

34
with the evaluation of ingredient data only when some are unknown.

Direct execution begins with the known input quantities, and proceeds to

evaluate all higher level data starting with the data directly dependent

on the input.

Conditional execution is appropriate when the computer is used to check

only a few of the possible constraints where a criterion applies; this

is the usual mode of use in design and in review. Direct execution is

suitable when substantially all derived properties are needed for the

given values of the input data. This may occur in certain large volume,

low- level design and detailing applications, and in review for some

types of specifications. Systematic approaches to efficient data

processing for both strategies are briefly discussed below.

For conditional execution, we have developed a single general operator,

called SEEK (23, 6), which uses the information network and the status

indicator discussed in the preceding section to recursively computer

only the ingredients actually needed and set their status to valid.

Another elemental activity in design is to change the value of a design

variable. Use of the information network allows a recursive WARN

procedure (23) to set to void the status of each datum which would be

affected by the change. It would be possible to reevaluate the affected

data immediately. However, if a number of data are to be altered,

immediate reevaluation would be wasteful. When data are needed again,

SEEK is used to selectively reevaluate only the data affected by the

changes

.

35
When the number of criteria to be evaluated can be restricted to a relatively small number defined in advance, it is entirely feasible to

develop an efficient constraint processor using direct execution. The

order of computation may be generated directly by expressing the global

information network of the required portions of the specification in

post order (11) . Then, using the subscripted ingredience relationships

defined above, computations may be carried out systematically to evaluate

all dependents, rising in the information network from the input data to

the highest level criteria.

Organizational Level

In constraint processing, the organizational level acts as a switching

network or directory to lead the process to the execution of the

appropriate constraints. In conditional execution, especially in an

interactive (time-shared) environment, the user can specify the node(s)

of the argument trees where he intends to begin constraint processing.

For direct execution, the argument trees are used directly to sequence

the computations for efficient processing. As with the other two

levels, the application programs can be substantially improved in size

and speed by pre -specifying the subtrees comprising the criteria to be

incorporated into the programs.

36
7. SUMMARY AND CONCLUSIONS

We have presented an abstract representational model of design specifications, and have identified the formal properties of completeness,

uniqueness, and correctness which every design specification should

possess. The formal representation consists of decision tables or

derived decision trees for the provisions, an information network for

interrelated provisions, definitions and evaluation procedures, and

argument trees for organizing and outlining. We have identified methods

for formulating specifications, and tools for checking them for the

requisite properties. We described a number of strategies for expressing

specifications in textual form, and the relative advantages of each.

Finally, we have shown the extensions necessary to apply the procedures

discussed to the generation of computer aids for processing project

design data against the specifications for design and conformance

checking

.

Our study demonstrates that the concepts of performance and limit states

need to be an integral part of specification development to insure that

the users know the intent of the specification and can correctly apply

its writers' intentions. We have indicated how the formal representation

may be used to generate alternate formats for distinct users, say, for

experienced designers, students, and building officials. We have shown

how computer aids may be used in formulation and expression to reduce

the cost and uncertainties in specification developments. While the

prime use of these tools is in the synthesis of new specifications, the

37
benefits accrued from the formal representation and purposeful expression

may be great enough to warrant review and clarification of existing

specifications without major changes in scope or technical content. We

have also demonstrated that the generation of computer aids based on the

specifications can and should be made an integral part of specification

development.

The methods presented have been tested in the analysis of a number of

diverse specifications and are considered reliable. There is need,

however, for further systematic studies in formulation and expression of

specifications, especially in the evaluation of the strategies of expression

described.

It is our hope that through the methods presented, specification

development can become a much more integral part of the transmission and

implementation of research results, and that design specifications will

no longer be looked upon by designers as a necessary evil, but as a

constructive aid in achieving design objectives.

38
STRESS TYPE: TENSION. COMPRESSION

MEMBER TYPE: MAIN. SECONDARY

MEMBER DETAILS: ROD. PINHOLE, STIFFENER. WEB

DESIGN OPTION. SLENDERNESS CHECK DESIRED

TENSILE STRENGTH

YIELD STRESS

MODULUS OF ELASTICITY

EFFECTIVE LENGTH FACTOR

LENGTH

RADIUS OF GYRATION

Figure 1. Information Network for Allowable Stress

and Slenderness Ratio Criteria

39
TYPICAL SUBNETWORKS

Figure 2. Schematic Information Network for Tension

and Compression Member Criteria

40
I SYSTEM )

-( MAIN

J—(SECONDARY]

b ) PERFORMANCE ATTRIBUTES AND LIMIT STATES

Figure 3. Argument Trees

41
Figure 4. Decision Tree for Maximum Slenderness Ratio Criterion

42
ACKNOWLEDGMENTS

The work reported herein has benefited from the contribution and

comments of many people. We wish to acknowledge specifically our

colleagues, Professors E. H. Gaylord, Jr., J. W. Melin, R. L. Tavis,

and Mr. R. J. Kapsch, and our former students, Drs. S. K. Goel and

D. J. Nyman. The American Institute of Steel Construction provided the

initial financial support and practical perspectives to this work. The

University of Illinois, Carnegie-Mellon University, and the Center for

Building Technology of the National Bureau of Standards also have

supported these studies.

43
REFERENCES

1) Allen, D. E. , "Limit State Design - A Unified Procedure for the

Design of Structures," The Engineering Journal , Vol. 53, No. 2 (Canada: np, 1970), pp 18-25.

2) Building Code Requirements for Reinforced Concrete , ACI 318-71

(Detroit: American Concrete Institute, 1971).

3) Building Officials and Code Administrators Basic Building Code

(Chicago : Building Officials and Code Administrators, Inc., 1975)

.

4) Commentary on the Specification for the Design, Fabrication and

Erection of Structural Steel for Buildings (New York: American

Institute of Steel Construction, 1969)

.

5) Fenves, S. J., "Tabular Decision Logic for Structural Design,"

Journal of the Structural Division , Vol. 92, No. ST6 (New York:

American Society of Civil Engineers, 1966), pp. 473-490.

6) Fenves, S. J., "Representation of the Computer -Aided Design Process

by a Network of Decision Tables," Computer and Structures , Vol. 3,

No. 5 (1973), pp. 1099-1107.

7) Fenves, S. J., Gaylord, E. H. , Jr., and Goel, S. K., "Decision

Table Formulation of the 1969 American Institute of Steel Construction

Specification," Civil Engineering Studies , No. SRS 347 (Urbana:

University of Illinois, 1969).

8) Goel, S. K. , and Fenves, S. J., "Computer-Aided Processing of

Design Specifications," Journal of the Structural Division , Vol. 97, No. ST1 (New York: American Society of Civil Engineers,

1971), pp. 463-479.

9) Guide Criteria for the Evaluation and Design of Operation BREAKTHROUGH

Housing Systems , Report 10200, 4 Volumes (Washington, D.C.: National

Bureau of Standards, 1970).

10) HUD Minimum Property Standards (One and Two Family Dwellings (No.

4900.1), and Multifamily Housing (No. 4910.1)) (Washington, D.C.:

U.S. Department of Housing and Urban Development, 1973).

11) Knuth, D. E., The Art of Computer Programming, Vol. I: Fundamental

Algorithms (New York: Addison-Wesley, 1968)

.

kU
12) Noland, J. L. , and Feng, C. C, "American Concrete Institute

Building Code in Decision Logic Table Format," Journal of the

Structural Division , Vol. 101, No. ST4 (New York: American Society

of Civil Engineers, 1975), pp. 677-696.

13) Nyman, D. J. , and Fenves, S. J., "An Organizational Model for

Design Specifications," Report R73-4 (Pittsburgh: Carnegie-Mellon

University, 1973)

.

14) Nyman, D. J., and Fenves, S. J., "An Organization Model for Design

Specifications," Journal of the Structural Division , Vol. 101, No.

ST4 (New York: American Society of Civil Engineers, 1975), pp.

697-716.

15) Nyman, D. J., Fenves, S. J., and Wright, R. N. , "Restructuring Study

of the American Institute of Steel Construction Specifications,"

Civil Engineering Studies , No. SRS 393 (Urbana: University of

Illinois, 1973).

16) One and Two Family Dwelling Code (Promulgated by Building Officials

and Code Administrators, American Insurance Association, Southern

Building Code Congress, and International Congress of Building

Officials) (1971).

17) Pollock, S. L. , Decision Tables: Theory and Practice (New York:

Wiley- Interscience, 1971).

18) Seeberg, P. , "Decision Table Formulation of the Specification for

the Design of Cold-Formed Steel Structural Members" (Milwaukee:

University of Wisconsin, 1971)

.

19) Siess, C. P., "Research, Building Codes, and Engineering Practice,"

Journal of the American Concrete Institute , Vol. 31, No. 11 (May

1960), pp. 1105-1122.

20) Specification for the Design, Fabrication and Erection of Structural

Steel for Buildings (New York: American Institute of Steel Construction,

1969).

21) Ventre, F. T. , Social Control of Technological Innovation: The

Regulation of Building Construction (Unpublished doctoral dissertation)

(Cambridge: Massachusetts Institute of Technology, 1973).

22) Wright, J. R. , "Performance Criteria in Buildings," Scientific

American, Vol. 224, No. 3 (March 1971), pp. 16-25.

45
23) Wright, R. N. , Boyer, L. T., and Melin, J. W., "Constraint Processing

in Design," Journal of the Structural Division , Vol. 98, No. ST1

(New York: American Society of Civil Engineers, 1971), pp. 481-

494.

24) Wright, R. N. , Nyman, D. J., and Fenves, S. J., "Restructuring

Study of American Institute of Steel Construction Specification"

(Unpublished progress report) (Urbana: University of Illinois,

1971).

25) Yang, J. M. , and Fenves, S. J., "Representation of Information in

the Design- Construction Process," Report R74-1 (Pittsburgh: CarnegieMellon University, 1974)

.

46
NBS-114A (HEV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSTN 940

2. Gov't Accession

No.

4. TITLE AND SUBTITLE

The Representation and Use of Design Specifications

3. Recipient's Accession No.

5. Publication Date June 1977

6. Performing Organization Code

7. AUTHOR(S)

S.J. Fenves and R.N. Wright

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiect/Task/Work Unit No. 4600900

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Design specifica

tool for the des

completeness, un performance and

tions are emphas

levels: decision

for related prov

idealized proces

the representati

gies for textual

computer aids fo

is described.

tions are presented as the primary communication and control

ign and construction industry. Requisite properties of

iqueness and correctness are identified, and the role of

limit state concepts in specifying intent of the specificaized. Formal representation methods are presented at three

tables for specification provisions, an information network

isions, and argument trees for organizing and outlining. An

s for specification development is presented, and the use of

onal tools for checking specifications and providing strateexpression is described and illustrated. Development of

r specification processing in design and conformance checking

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first, key word unless a proper name; separated by semicolons) Building codes; computer programming; decision tables;

graph theory; performance specifications; standards.

18. AVAILABILITY DC Unlimited

_j For Official Distribution. Do Not Release to NTIS

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NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. It is published in two

sections, available separately:

• Physics and Chemistry (Section A) <jl' Papers of interest primarily to scier' »,, orking in these fields. This section covers a br ^^ .ige of physical and chemical research, wit v ^-^ jr emphasis on

standards of physical measu*- y* , fundamental constants, and properties of mr ^'.dsued six times a year. Annual subscription: D- e \

0>>-, $17.00; Foreign, $21.25. • Mathematical Sci' vp^v Section B)

Studies and comr %* .is designed mainly for the mathematician and .qC dtical physicist. Topics in mathematical statis* ' .c^.ieory of experiment design, numerical

analysi r ^^retical physics and chemistry, logical design a<* programming of computers and computer syst

r Kr*_,nort numerical tables. Issued quarterly. Annual

stocription: Domestic, $9.00; Foreign, $11.25.

DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews

such issues as energy research, fire protection, building

technology, metric conversion, pollution abatement,

health and safety, and consumer product performance.

In addition, it reports the results of Bureau programs

in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing.

Annual subscription: Domestic, $12.50; Foreign, $15.65.

N0NPERI0DICALS

Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. . Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such

as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396).

NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

Reference Data (JPCRD) published quarterly for NBS

by the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements available from ACS, 1155 Sixteenth

St. N.W., Wash. D. C. 20056. Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental

functions and the durability and safety characteristics

of building elements and systems.

Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under proce- dures published by the Department of Commerce in Part

10, Title 15, of the Code of Federal Regulations. The

purpose of the standards is to establish nationally rec- ognized requirements for products, and to provide all concerned interests with a basis for common understanding of the characteristics of the products. NBS

administers this program as a supplement to the activities of the private sector standardizing organizations.

Consumer Information Series—Practical information,

based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order above NBS publications from: Superintendent

of Documents, Government Printing Office, Washington,

D.C. 20402. Order following NBS publications—NBSIR's and FIPS

from the National Technical Information Services,

Springfield, Va. 22161. Federal Information Processing Standards Publications

(FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Services (Springfield, Va. 22161) in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A

literature survey issued biweekly. Annual subscription: Domestic, 825.00 ; Foreign, 830.00'. Liquified Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: 830.00 . Send subscription orders and remittances for the pre- ceding bibliographic services to National Bureau of Standards, Cryogenic Data Center (275.02) Boulder,

Colorado 80302.
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