Experimental adaptive
interface
M V Mason and R C Thomas

Software often has to interact with end users. It is thus o finterest to software designers to consider the incorporationo f useful man-machine interface techniques into theirsystems. The present article seeks to transfer knowledgeo f adaptable interfaces to the information retrieval com­munity. An experiment at Leeds University into adaptive
interfaces fo r the online UNIX* manual is described,
together with an overview o f some o f the design issues.
The relevance o f dialogue monitoring as a source o f data
fo r determining the model o f user behaviour is discussed
as is the design o f dialogue generating programs that canmodify their output to suit the user model.
Keywords: computer software, man-machine interface,
information retrieval

IN T R O D U C T IO N
For any human-computer system to enjoy success, thedesign of an effective man-machine interface (MMI) is an
essential prerequisite. A wide range of information systems
including expert systems, database systems and electronic
publishing systems need to make use of appropriate inter­face engineering principles in order to produce a systemthat is acceptable to users.
An example where considerable effort has been spenton interface design for database applications is the
ROBOT system1, which features a natural language
query interface. The BCS Query Languages Group 2 also
discusses techniques for effective query language design.
Many of these reported techniques are standard MMI
approaches, for example menu selection, which arewidely used in non-database systems3.
Given the need in all information systems, including
databases, to engineer high-quality interfaces and that to
do so requires effective use of MMI design principles, thisDepartment of Computer Studies, University of Leeds, UK•U N IX is a trademark of Bell Laboratories

162

article seeks to introduce to the information retrieval
community some techniques concerned with the design ofadaptable/adaptive interfaces. Design issues relevant tothe construction of this form of interface will be discussed
in relation to our experiments on the provision of an
adaptive interface to die online U N IX manual. Prior to
the discussion, however, we briefly review work on elec­
tronic reference book systems as it provides the context
for our experiment.
E L E C T R O N IC R E F E R E N C E B O O KSY ST E M S
There is some discussion in the literature concernedwith the implementation of electronic books. Opportunities
in this area range from the simulation of paper books inelectronic fo rn rto the exploitation of the computer-based
media to manipulate book information in hitherto imposs­ible ways5.
We are particularly concerned with the discovery ofgeneral engineering principles required in the design ofelectronic reference books. In particular, our research
efforts concentrate on examination of the applicability ofthe electronic medium to online software manuals.
Authors such as Sohr6 and Maynard 7point out that for
many software systems, paper reference manuals ideallyneed to meet a variety of differing information needs (e.g.,some users require reference information only, whilst
others require detailed help information). Invariably, anattempt to satisfy all user needs fails — in essence paper
software manuals cannot be ‘all things to all men’. Prelim­
inary investigations into the use of the online U N IX
manual at Leeds University suggested that this basic
problem of paper software manuals also existed in thatelectronic manual (see section on monitoring data).
W hat is ideally required is a manual that can alter its
characteristics to suit the particular needs of users con­sulting it. We refer to such a manual as an adaptablemanual.

0144-817X /84/030162-06$03.00 © 1984 Butterworth & Co (Publishers) Ltd

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It is proposed that the construction of a fully adaptablemanual will need to incorporate mechanisms which:• automatically adapt information search methods,• automatically tailor knowledge in the book according
to specific information needs (e.g., the level of detail in
displays of reference information changes to suit users
with widely different levels of technical knowledge),• permit users to organize the layout of information
displayed on the screen as they require.
The technology of adaptable/adaptive interfaces provides
some of the tools needed to build an adaptable manual, butthere are other research issues such as appropriate
knowledge representation formalisms and text generation
mechanisms that lie outside the scope of the current
project.
We now examine some of the key concepts in m anmachine interface work that have proved useful in the
project.
A N O V E R V IE W O F A D A P T A T IO N A T T H E
IN T E R F A C E
A central concept to the study of the man-machine inter­face is that of the user model. In this context, the term‘user model’ refers not to some scheme for user categoriz­
ation, e.g., casual or dedicated user, but rather to theuser’s conceptualization or personal image of the systemwith which he is interacting8.
Authors such as Nickerson 9 and Young10point out thatwell formulated user models, where the user has a clear
conceptualization of the interactive system, positively
assist him during interaction, and that conversely he isactually hindered by poorly formulated models. Indeed,
M oran 11 believes that during the interface design process
the system designer should construct a conceptual modelof the system for the user to learn. The interface should
possess features such as an adequate degree of interactive
feedback that will allow the user to assimilate an appro­
priate conceptual model of the system as easily and aseffortlessly as possible.
Sometimes a poor user model can have disastrous
consequences as exemplified by Weizenbaum’s 12 famous
program ELIZA, which was capable of simulating thetype of dialogue that might occur between patient andpsychiatrist using keyword-based rules to transform
input sentences. The resulting dialogue was so convincing
that, despite the fact that ELIZA did not attempt to‘understand’ user responses, many users conceptualized
the system as being intelligent and capable of appreciating
their feelings.
The user’s conceptualization of a computer system is
not static but changes, for example, as the user gains
greater experience of the system. Furthermore, manysystems have a number of users, each with varying
degrees of knowledge, experience and requirements andthus with different user models.
For the purposes of this paper, we wish to distinguishthree approaches to adaptation at the interface:• Adaptable interfaces which provide programmablefacilities so that the user can alter the interface tosuit himself.
• Adaptive (or self-adaptive) interfaces which are capableof changing themselves automatically in an appropriate
fashion. Typically they need to formulate some model

vol 3 no 3 1984of the user which might simply consist of a descriptive
set of variables which is sufficient to discriminate
between individual users or user types. In a more
complicated approach, which is suitable for dialogues
with relatively few interactions between user and com­puter, Rich 13,14 has built a user-modelling system that
embodies stereotypical knowledge concerning humancharacteristics.
• Adaptive dialogue design in the sense that the interface
evolves gradually via the production of a number ofsystem prototypes. For example, when Alsberget a /.15
built a database interface driven by a microcomputer
and touch-sensitive display, they found that, eventhough the system was easy to use, there were some
subtle requirements that simply could not be predictedby the designer.

O V ER V IEW O F T H E C U R R E N T
E X P E R IM E N T
In this section we describe the major features of our system.
Justification for our approach can be gained fromexamination of the issues presented in the literature
review above.
Current system
The information in the existing online Unix manual isorganized into eight major sections. For example, section
one contains information on the general commands avail­able to users, while section eight has system maintenancecommands. The manual information is retrieved when auser invokes the Unix man command. So, for example,
man pcretrieves the manual article on the pascal compiler called‘pc’. The user may specify an appropriate section number
if desired. Thus
man 5 termcap
retrieves the manual article on the system’s terminal
capability database (termcap) in section 5, which isdenoted by termcap(5). Note though thatman termcap
retrieves the termcap(3) article. If a section number is not
specified, then the manual searches progressively throughits sections in order.
Consistent with the Unix philosophy of modifying acommand’s behaviour by the setting of flags, man offers anumber of options. For example, the -k flag performs a
simple keyword search so if the user types
man -k pascal compilerthen references to all manual articles with the keywords
pascal or compiler in the name field will be listed. The
implicit inclusive OR has the drawback that references toall compilers are listed.
Other flags enable the user to obtain brief details ofcommand usage and one line descriptions of systemcommands.
The current interface can be criticized for:• its lack of cues to help the user conceptualize the struc­ture of the manual as an electronic book with sections,163• its lack of indexing features,• its poor keyword search,• its rather incomprehensible article style,• poor facilities for browsing through a selected article,
sometimes called page flipping.

First experim ental version
Features
The philosophy of the system prototyping approach todesign has been used so that our basic design strategy forthe first version has been to implement a small, but one
hopes useful, set of features with the intention that this will
motivate users into suggesting new facilities that theywould find useful. There is some evidence that this is startingto happen.
The first version of the pilot adaptable manual isupward compatible from the old manual in that the samefeatures (such as keyword search) are still available.
However, the new interface has been designed to assist theuser in conceptualizing the system as an electronic bookas well as possessing new features, which include:• Page flipping. Users can flip backwards and forwards
within and between articles.
• Command prompting. When a normal article is displayed,
the terminal screen is divided into two windows. The
top window displays one page of manual text whilst thebottom window displays a set of command prompts. As
the user’s experience of the system increases (as judged
by the user-modelling mechanism) the command prompt
window decreases in size (allowing more manual text
to be displayed). In addition, the nature of the prompts
changes such that prompts for sophisticated commands
are displayed to the more experienced users.
• Indexes. An index for each section of the manual has
been provided as another means of locating relevant
information. An adaptive dialogue assists the user insearching these indexes. It includes explanation of thescreen layout and terms, a prompt window, and theability to use a menu or flag driven dialogue.
• Glossary. If the user does not know the meaning of aphrase in the window, he can request an explanationfrom the built-in glossary by simply placing the cursor
on the word and pressing ‘g\ Any requests which cannot
be answered are stored so that the relevant glossary
entry can be added later.
• Cross referencing. While reading an article, the user can
ask for any manual information on material by placing
the cursor on the word and pressing ‘m’. If a suitable
article exists, it will be displayed once the user has
finished reading the current item.
• Help. While viewing a manual article a user canrequest information without needing entirely to abandon
the currently displayed article (unlike in the existing
manual). The help information given depends on thesystem’s model of the user, i.e., the help system
dialogue is adaptive. There may be some advantage inpresenting help information on the use of the adaptablemanual in the same way as information on U N IX ispresented by the manual. This gives a recursive flavour
to the electronic book system. This ‘recursive architec­
ture’ could conceivably map naturally into systems
providing many levels of help information.

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Provision of adaptation
The manual’s adaptive processes are driven by a simple
model of the user that attempts to quantify the user’s
experience at using the system. Currently such usermodelling is based on a combination of rules and weightingof a set of user-descriptive variables.
For example, to select the appropriate article display,users are graded into classes from TYPE1 through to
TYPE4. The TYPE1 user is given explanation materialand substantial prompting from the system. On the other
hand, the TYPE4 user is immediately presented with thetext and given only the prompt ‘For help type h’. The usermodeller initially classifies the user according to a set of
hypotheses. An example of such an hypothesis is:
Hypothesis: ‘The TYPE2 user should be upgraded
to TYPE3’
VI: the user has used the system more than twice(w = 0.25)
V2: commands x andy used in last retrieval (w = 0.20)
V3: help not used more than once in last retrieval(w = 0.25)
V4: the user has used the system within 5 days
(w = 0.30)
Variables Vi have values of either 1 or —1 depending onwhether or not the condition is true or false. A weighted
result is calculated (in this case the sum of the wi times Vi)
and tested against some prespecified threshold figure. If
the result is greater than or equal to the threshold then theuser is upgraded; if the result is less than the threshold thenthe user classification remains unaltered.
M onitoring data
This section gives a brief comparison of the data obtained
from monitoring the usage of the standard manual (here­
after referred to as the ‘standard manual’) with thatobtained from monitoring the adaptable manual. In bothcases two records were made:• ‘Log of Manual Transactions’. Each transaction
record comprised three fields:
o user name,O time at which the command was invoked,
O command arguments.
• ‘Accounting Information’. A log of all systemcommands permitting the context in which the manual
was invoked to be analysed.
Overall manual usage
The usage of the standard manual was recorded over a five
week period (i.e. 25 working days) in the first term of the
1983-1984 session. During this period there were 1709
manual consultations with a total of 85 different users
making use of the system. The usage of the adaptablemanual was also recorded over a five week period in thesecond term of the session. In this case 3329 consultations
took place and the system was used by 134 users.
In terms of the proportion of the U N IX user populationthat made use of the man command, the mean daily percen­
tage use of the standard manual was 30.9 per cent (standard
deviation: 2.9 per cent) whilst the corresponding statistic
for the adaptable manual was 40.6 per cent (standard
deviation: 6.4 per cent).

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These results should be interpreted with great caution.
Before the adaptable manual was installed, there were twosimilar commands: man and help. The latter had two func­
tions: a simple two page help message, and also as anentry into the manual. Thus some manual usage may havebeen disguised as help usage. When the adaptable manual
was installed, the' help command was removed. The
figures for help were mean of 17.5 per cent (standard
deviation: 4.6 per cent).
Unsuccessful transactions
In assessing any interactive system one typical area ofinterest is the frequency of unsuccessful transactions.
These occur either because of a user syntax error or
because, even though the syntax is correct, the requested
information is not in the database.
For example, consider the command line:$ man pascal compiler
The standard manual simply informs the user that thearticle ‘pascal compiler’ does not exist and then quits. The
adaptable manual, on the other hand, automatically
invokes the keyword search facility prompting the user
with the line:
pc ( 1) — pascal compiler
The mean daily percentage of unsuccessful transactions
from the standard manual was 12.9 per cent (standard
deviation: 6.2 per cent) and for the adaptable manual was
13.5 per cent (standard deviation: 4.5 per cent). The
increase for the adaptable manual does not appear to besignificant and similar types of unsuccessful transaction
occurred in both systems. However, the adaptable manual
does deal with unsuccessful transactions in a somewhat
different fashion from the standard manual.
SearchA significant difference between the manual versions wasthat the number of transactions devoted to searching forarticles increased in the adaptable manual. In the standard
manual keyword searching only was available and themean daily percentage of transactions concerned with thisfacility was 4.9 per cent (standard deviation: 4.5 per cent).
For the adaptable manual, however, as previously stated,
an index search facility was included. In this case die mean
daily percentage of keyword search transactions was 3.4
per cent (standard deviation: 2.3 per cent) and thecorresponding figure for index searching was 7.3 per cent(standard deviation: 3.3 per cent). Indeed, searching byindex proved to be a quite popular facility.
Anecdotal evidence
User comments were recorded via the mail system andalso noted from informal conversations. It became
clear that users were generally not prepared to spend agreat deal of time learning how to use the system (after allusers consult the manual to facilitate the completion ofsome main computing task), but they did expect thesystem to possess many of the features that they had
encountered in sophisticated text editors. Typicalexamples of suggested facilities were cursor motion byword, bookmarking facilities and within-text searching
using regular expressions to specify patterns. This

vol 3 no 3 1984

undoubtedly causes something of a paradox as users
typically invest a substantial amount of time and effort inlearning how to use text editors that possess a comparable
set of functions. The problems caused by this paradox areof current research interest. However, although users
were given no training nor in-depth documentation on how
to use the existing adaptable manual there were few
reported difficulties concerning system use. In this respect,
it seems that the adaptive interface has made a significant
contribution and this can be seen as a sign of encourage­
ment in the design of a future adaptable manual system.

D E S IG N IS S U E SThis section provides an overview of some of the design
issues found to be relevant to the adaptable manualsystem.
D ialogue m onitoring
The recording of the interactive exchanges between userand system by dialogue-monitoring software has contributed
significantly to the design of the adaptable manual. For
accounts of approaches to and benefits from dialogue
monitoring in other systems see Abrams et a h 16 andGainer et al. 17.
A dialogue monitor can be used for:• Obtaining information on the use of some existing
system in a manner akin to the systems analysis
technique of observation. Moreover, insight can begained into whether or not the user population ishomogeneous or heterogeneous in nature and hence
indicate the justification for building an adaptive(in the heterogeneous case) or non-adaptive (in thehomogeneous case) interface.
• Obtaining evaluation information useful in checking
the design of the interface.
• Obtaining feedback information which is required if asystem prototyping approach to design is being used.
D evelopm ent m ethodology
The intention is that the adaptable manual should be selfadaptive, although the system is also being developed via
a system-prototyping strategy (as discussed in the section
on adaptation at the interface) in order to obtain smoothinteraction at all levels of dialogue.
D ialogue-generating programs
Dialogue design typically involves the specification andimplementation of a set of production rules (equivalent to
the rewriting of formal grammars) or alternatively a finite
state transition network that defines the dialogue.
Guest 18has investigated the use of two dialogue-design
tools at Leicester Polytechnic, one of which relies on a
production rule input to generate an interactive dialogue,
while the other requires a transition network representationof the interface. From this study there seems to be someevidence to suggest that the network formalism is a some­what easier approach to interface design. Certainly, all165

dialogues in the adaptable manual have been designed interms of state transition networks.
The use of state transition networks for dialogue design
have been reported by a number of researchers such as
Pam as19, Denert 20 and Edmonds21. Given certain slightnotational differences between the network schemes
recommended by different researchers, the state transition
network is essentially a collection of arcs and nodes
forming a directed graph. At each node, relevant output
text is generated by the system. The corresponding
response from the user causes the selection of an arc(which the designer has specified as being uniquely
associated with the particular form of the input given by
the user) emanating from the current node. Subsequently,
an arc transition occurs and a fresh set of output text is
displayed when the next node in the network is reached.
This process is repeated so that the progression of the
man-computer dialogue involves successive transitions
from node to node in the network.
In the first version of the adaptable manual the interface
to each facility is implemented as an individual dialogue­
generating program (thus the complete system consists ofa collection of such programs). The ability of programs tobranch from one to another permits dialogue transition
from facility to facility. A t the highest level, therefore, theinterface to the manual can be regarded conceptually as a
virtual transition network with transition arcs connecting
the dialogue-generating programs together. Indeed, thelatter essentially form subnets of the top level virtual
network. The representation of these subnets is explicit
and has been implemented in the C programming
language.
Currently, the manual facilities which generate adaptive
dialogues possess their own individual user-modelling orclassifying mechanisms. The attraction of this approach
was seen as minimizing the degree of coupling between
programs, and making each facility as highly cohesive as
possible, as well as being a simple way of managing
adaptation (a user may be expert at using one facility but anovice using another).
Given some particular manual facility with an adaptive
interface, immediately prior to the user interacting withthis facility, the user is inferred as belonging to someappropriate user class. Relevant arcs are then enabled or
disabled on the transition network (representing the
dialogue for the facility) in order to provide an interface
appropriate for that user. During the subsequent interaction
further adaptation may be required and this is achieved by
the use of a number of rules that use knowledge of thecurrent user class and the network topology to reclassify
the user if appropriate.

Perform ance
The construction of an adaptive interface naturally
requires additional processing. This overhead may affectthe performance characteristics of the system.
For the adaptable manual system, the additional
processing costs can possibly be reduced by restructuring
the organization of the manual information. It is likely thatsome manual articles are more frequently retrieved byusers than others. If this can be established from thedialogue-monitoring statistics, then the manual information
storage scheme can be recognized to promote particularly
speedy retrieval of popular articles.

166

The other major problem with performance is that theuser may perceive the manual to be slow, when in fact it isdoing the work of several transactions in the old version.
Overall, therefore, it may not be as slow as users some­times believe.

Terminals
We believe that the electronic book medium should be
upward compatible from the paper book medium. One
argument to support this is that the user’s conceptualizationof a system into a user model is partly based on previous
experiences and prior ways of thinking. Therefore, it canbe expected that there will be a tendency for electronic
books to be conceptualized in terms of previous ‘natural’(i.e., paper based) ways of reading texts in books. This
basic book model provides a convenient foundation onwhich the engineering of computer-based books can belaid. It is envisaged that the technology of adaptable/
adaptive interfaces allows the user’s view of the electronic
book to be gently modified (at a pace appropriate to theuser) such that the user initially interacts with an electronic
simulation of a paper book and is gradually revealed new
text manipulation and information retrieval facilities thatare realizable only in very powerful forms of electronicbook.
Given that the initial user view of an electronic book is
to be analogous to the paper book the interface should
reinforce this conceptualization of the system. To thisend, systems such as the ICL PERQ, which have highresolution displays capable of simulating sheets of paper,
seem ideal for electronic book application, barring their
physical size.
Our experiences in electronic book design also indicatethat direct input devices such as the mouse or touchsensitive keyboards as well as the ability to organize thedisplay screen into a number of windows are also desirable
features for this application area.

C O N C L U S IO N S
It has been pointed out that the system designer of any
information system must take particular care in designing
the interface. This, in turn, requires the effective utilizationof well established MMI techniques.
This article has introduced one particular MMI
approach which introduces the notion of adaptation at
the man-computer interface. In relation to the task ofretrieving information from an online software manual,
this adaptive approach appears to have potential andprovides opportunities for implementing an enhanced
interface that is superior to the existing system.
Interface adaptation seems well suited to complex
systems where users vary in their expertise at using thesystem. Indeed, a system that possesses a static interface
initially requires the user to adapt to the rigid propertiesof the system and this places a considerable workload on
the user (which is uncomfortable). Adaptation at the inter­
face, however, allows the distribution of this workload
between system and user (both system and user adapt toeach other) and, as such, should promote more comfortable
and smoother human-computer interaction.

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