The Use of Metaphors in Iconic Interface Design

Stephen Richards, Philip Barker, Ashok Banerji, Charles Lamont and Karim Manji

Interactive Systems Research Group, Human-Computer Interaction Laboratory School of Computing and Mathematics, University of Teesside, Cleve, and, United Kingdom

Abstract

Much of the success of iconic interfaces has occurred within application domains in which a consistent metaphor can be maintained. However, this approach can prove problematic when icons are designed for cross-cultural applications - where a generic metaphor can often prove elusive. Even when a suitable metaphor can be found the problem remains of developing icons (within a given metaphorical framework) for all the functionality that may be required. Within certain application domains this difficulty has been overcome by means of the parallel use of more than one metaphor. This is certainly true of iconic interfaces to information delivery applications (where 'book' end 'travel' metaphors are relatively common). The universality of the book metaphor within modern culture and its relevance to many of the cognitive tasks involved in information delivery applications have provided the primary I motivation for out adoption of this metaphor in much of our work. However, we have also used multiple metaphor techniques for certain types of application. In this paper we describe the inter-relationship that exists between icons and metaphors and discuss the problems of designing iconic interfaces that embed useful metaphors. Various case studies are used to illustrate the issues raised and some outline conclusions derived from our work in this area are then presented.

 

Introduction

Icons are used extensively for communication purposes. The term icon has been adapted from its Russian origins -'ikon' meaning a religious painting or statue. Within the context of computing the word is used to refer to a small image which embeds 'meaning'. More specifically, an icon is a symbol or graphic representation (on a VDU screen) of a program, resource, state, option or window. As such, icons form an important part of graphical user interfaces (Barker, 1989). Icons used in such interfaces are usually (but not always) 'reactive' - that is, they can be used to initiate various types of process when selected by a user.

Due to the technological improvements that have taken place in computer hardware and software over the last few years (particularly with respect to graphics handling) the use of icons within graphical user interfaces has become extremely popular. The 'hour glass' and the 'trash can', for instance, are now familiar examples to most Windows and Macintosh users. Indeed, as a result of this popularity a number of different types of icon have now been developed. Currently, some of the most popular of the new developments are 'picons', 'micons' and 'earcons'. Picons are essentially icons that embed a picture (as opposed to a symbol). Similarly, micons are composed of moving pictures or video clips. Earcons, or auditory icons, are based upon the use of sounds and are usually embedded in sonic sequences (Gayer, 1989).

Iconic techniques are now used to support a wide range of functionality in a large number of different types of computer-based application. Many of these applications also embed interface metaphors - either by design or by accident. A metaphor can be defined as the use of an idea or object in place of another to suggest a similarity. The importance of metaphors lies in their ability to initiate cognitive transfer from one (familiar) knowledge domain to another less familiar one.

Metaphors are very much part of our everyday lives - so much so that we are often unaware that we are actually using them (Lakoff and Johnson, 1980). An example of this unconscious use of a metaphor can be seen in the following example. If we were to say 'Let's take a look at metaphors in language' (for instance) we would be using a 'seeing' metaphor in the context of describing a concept. It is not surprising then, that the use of metaphors can also become unconsciously embedded in human-computer interfaces. Just as they permeate everyday life - so they also permeate human-computer interfaces (Erickson, 1990).

The overall impact of metaphor use in iconic interfaces can be twofold. First, metaphors can play a part in the development of a functional specification. Indeed, metaphor usage should be made explicit at the design stage of application development so that maximum benefits can be attained. In this way a whole range of functions can be identified for which icons are required. In addition, metaphors can assist interface design by providing ideas for individual icon designs.

Second, the use of metaphors can have a significant impact upon end-users. Within an end-user interface metaphors can provide cues for the recognition of iconic symbolism. Also, the appropriate use of metaphors can provide a framework in which users can identify the functional meanings of icons.

Undoubtedly, one of the most well-known metaphors to be used in the design of iconic humancomputer interfaces has been the 'desktop metaphor'. This was very consciously used in the design of the Apple Macintosh desktop environment. In many other applications, however, the use of metaphors has not had such a high design profile. As a result, many applications make use of metaphors in iconic interfaces in ways which may be inconsistent and inappropriate.

In the remainder of this paper we attempt to illustrate the ubiquitous nature of metaphors within iconic interfaces by means of a number of application case studies. However, before describing these we discuss two other important issues. First, problems associated with designing and using icons. Second, the rationale for using metaphors within humancomputer interface systems. In the final part of the paper we present some outline conclusions derived from our work in this area.

Designing and Using Icons - Some Problems

One of the principal problems encountered with icons is their size. In most situations an icon must be small so as not to intrude on an application's workspace. For example, in the Microsoft Windows 3.1 desktop, the standard size of icons is 32 x 32 pixels. In many environments, the size of the icons is even smaller. This results in a limited message space, reductions in recognition potential, and also severe design constraints.

Another problem arises when trying to develop interfaces, which are internationally acceptable (Nielson, 1990). It can often be extremely difficult to find sets of icons which are useful across a number of different cultures. An example of this problem is provided by the flight of steps 'illusion'. When individuals from some cultures (including our own) view a line drawing of a flight of steps they actually see it as a three dimensional representation of a flight of steps. However, individuals from cultures where stairs are not used will see the drawing as a simple two dimensional design; they do not interpret it as a 'flight of stairs'.

Creating icons for every function can also prove problematic. In many modern computer-based applications system functionality is usually extremely high. The provision of many functions can mean the design of many icons. In addition, the screen space required for the display of a large number of icons can be very demanding thereby necessitating the development of suitable space-saving strategies for their display (such as 'icon grouping').

The way in which metaphors are used within an interface can also cause problems. An inappropriate or badly used metaphor can mislead users into believing that an event has occurred when it has not. Erickson (1990) gives an excellent example of this. He describes how an interface metaphor can, in some situations, suggest an incorrect model of a system and thus create difficulties for users. His example refers to the use of a voice mail system and the utilisation of 'mailboxes in which messages may be left'. The metaphor suggests that messages are transferred directly to a recipient's mailbox from a caller but, in reality, they are not. There can be substantial time delays leading to significant confusion for users if they do not really understand how the system works. Erickson suggests that the use of an 'answering service metaphor' would have avoided many of the problems users experience.

The level of communicativeness of an icon can also cause problems in iconic interfaces (Richards, 1990; Manji, 1990). In particular, when low or poor use is made of interface metaphors icons can be severely restricted in their ability to transmit their meaning, and thereby their function to users. In other words, even after recognition of the pictorial representation, the meaning within the context of the interface still needs to be recognised.

In addition, the communicativeness of icons can have major effects on both their learnability and their memorability. If an icon is highly communicative then it is much more likely to be easy to learn. In addition, icons which are easy to learn will generally be highly memorable. This is particularly true where the icon design is set within an appropriate metaphorical context which provides memory cues or prompts.

Using Metaphors in Iconic Interfaces

In order to use a computer-based application in an effective way it is important that users acquire an appropriate cognitive model relating to that application. The metaphors (and 'myths') that are embedded (either explicitly or implicitly) in an enduser interface to an application are powerful tools for the development of cognitive and conceptual models (Rubenstein and Hersh, 1984; Carroll, Mack and Kellogg, 1988).

Because of their importance we believe that metaphors should be used from the earliest specification and design phases of an application development project. Indeed, many system development methodologies now include metaphor design in their early conceptualisation stage. Of course, in situations where appropriate metaphors can be found and which provide precise system views, interfaces of significant effectiveness can be developed. The greater the precision of the system image produced by a metaphor - the less likely it is that ambiguous or erroneous images of the system will occur.

A comparative example of high-precision and low-precision metaphors can be found in books and documents. The document metaphor is of relatively low-precision since it can be associated with a wide range of target objects varying from a single piece of paper to a series of books. It can be part of a book or a book itself. It is very wide ranging and open to many interpretations. In contrast, the book metaphor is of relatively high-precision. A book is a collection of pages bound within covers. We would generally expect a book to have some form of index and the pages are organised sequentially.

Although the book metaphor is more precise than the document metaphor it should be remembered that sometimes metaphors which are less precise can be useful. For example, a building metaphor and an office metaphor provide significant diversity and scope for the inclusion of more precise metaphors within them. The 'rooms' metaphor described by Henderson and Card (1987) provides a good illustration of this. Wide ranging metaphors can thus provide controls for applications which exhibit a great deal of internal diversity - such as an office. However, it is important to remember that the structure that is provided within the metaphor must be relevant to the problems and tasks which are involved in the application.

Metaphors chosen for interface use must also be easy to represent. It is important that distinctive images which are representative of the desired functionality can be created in a limited presentation area. For example, the book metaphor must, through its metaphorical representation, relay to a user the image of: a book; a series of pages; a front cover; a contents list; and so on (Barker, 1991; Richards, 1993). In other words the metaphor provides a framework for the design of icons.

Understandability is, of course, another important aspect of interface design. Obviously, the interface that is derived from a metaphor must be a suitable one for the target end-user population that is to use it. If users fail to understand the implications of the metaphor (either consciously or unconsciously) then it is of no value. This becomes particularly critical in international iconic interfaces where it is even more diffficult to identify a useful metaphor.

Extensibility is another aspect of good metaphors for iconic interface design. The use of a good metaphor can provide ideas for improving the existing design. Extensions to the existing system may be suggested by properties of the metaphor which are appropriate to the system being designed. In addition, the parts of the metaphor which go beyond the current implementation can provide for additional functionality in the future.

With the complexity and high functionality which is a key aspect of many modern applications, a single metaphor may not support all the facilities which are needed. In such circumstances multiple metaphors can be used (Richards, 1993). One example could be a book and a travel metaphor that are embedded within an implementation of a hypermedia electronic book. This approach provides a user with several strategies for navigating through and retrieving information from a complex hypermedia knowledge corpus.

An area which can have a critical impact on the usability of future iconic interfaces is the idea of standards. Sets of recommended, tried and tested icons, based upon particularly useful, and culturally relatively common metaphors, could be produced. When such a metaphor is appropriate for a particular application, these tried and tested icons can be 'taken off the shelf' and used. In this way, similar functionality across a wide range of applications can be represented by a standard icon. Further, sets of standard icons would be used in different applications based upon the same metaphor. In this way, user experience would be highly transportable between different computer applications.

One strategy which can be used when a large number of icons is required is 'grouping'. This refers to a technique where icons are grouped together under a parent icon. When the parent icon is selected the group of icons attached to that particular parent icon become available. A good example of this strategy is provided by Publishers PaintBrush for Windows. When certain icons are selected a pop-up icon bar becomes available in a way similar to a pop-up menu. This system also uses a small cut-out in the comer of an icon to signify that it is functioning as a group icon.

Sometimes, the meaning of icons used to support a particular metaphor can be ambiguous and difficult to decode unless considerable care is taken in designing them. Therefore, one of the principle methods used for enhancing the meaning of icons is to use multiple modality. Text is the form of augmentation that is most frequently used to support the meaning of an icon. Two basic types of textual support can be used: permanent (or static) labels; and dynamic labels. Pemmanent labels are usually found attached to the base of an icon - as can be seen in both the Apple Macintosh and the Microsoft Windows desktops. Dynamic labels are less common; in this case the textual augmentation only appears once the mouse pointer is moved over its host icon. As well as textual augmentation, audio augmentation may also take place.

Of course, serious problems can arise from the use of textual and audio augmentation - particularly, with respect to international interface designs. Obviously, if an interface is intended for international use then any textual labels which have been attached to it must be dynamically switchable between the target languages.

Some Case Studies

In order to illustrate some of the concepts which have been discussed earlier in this paper several case studies are presented. These are based upon four commercially available products that are published on three different optical disc delivery technologies. The first of these products uses Compact Disc ReadOnly Memory (CD-ROM). The second uses 'Photo CD' and the third and fourth employ Compact Disc - Interactive (CD-I).

The most common digital optical storage and delivery technologies are based on a variety of CDROM standards. Undoubtedly, to date the most popular of these has been the ISO 9660 standard. However, others are becoming available. Of course, ISO 9660, Photo CD and CD-I are only three examples of the many different CD-ROM formats that are now available. The ISO 9660 standard is often referred to as 'CD-ROM' (a convention followed in this paper); other extended formats tend to be referred to by other acronyms such as CDROM XA, CDTV, and so on.

Case 1: Book Metaphors on Compact Disc

A large number of applications which embed book metaphors are available on CD-ROM. These are often referred to as 'electronic books'. They employ a wide range of end-user interfaces, including the use of icons. Book related icons are therefore becoming well established as a generic class. One application which makes use of such iconic interfaces is the Active Library on Corrosion (Bogaerts and Agema, 1992). The Active Library on Corrosion (ALC) is a hypermedia reading and reference resource which makes use of library and book related metaphors.

The software which underlies the Library on Corrosion is the Active Library System which is written in Guide (Brown, 1986). The idea behind this software is that it should provide a shell into which any number of different libraries can be loaded. ALC is an example of just one of many possible libraries that can be delivered using such a shell.

As well as using page numbering, a chapter structure, indexes, bookshelves, and so on, ALC uses a number of icons which are drawn from library and book metaphors. These include icons for page layout, for activating various books on the bookshelf, and page turning icons.

In addition, ALC also makes use of travel metaphors -however, to a much lesser degree. Travel-based metaphors are used in ALC for the provision of 'backtracking' and 'trail' facilities. The backtrack icon provides a facility whereby users can travel backwards and forwards through the information nodes which they have already visited. The fact that this is a hypertext system, where users can visit nodes, or pages, in any order makes this an important part of the interface.

The trail facility is represented by an icon depicting a 'country scene'. This relates to the idea of following predetermined paths through the environment. Of course, there can be many paths in the countryside, and even the opportunity to make new paths. Similarly, both facilities are provided in the electronic trail. A number of predetermined 'built-in' trails are provided with the system. In addition, users may also create their own trails through the information space. This is achieved by selecting nodes for inclusion in a personal trail which can be saved, reloaded, and followed again at a later date.

Another interesting feature of the ALC interface is the use of both local and global icons. Global icons refer to those which are available throughout the entire application, whilst local icons refer to those which only become visible within a particular context. In ALC a 'toolbar' consisting of a number of global icons is placed down the right-hand edge of the screen. These are always available and allow access to controls at the book level. Global book functions include: backtracking, trails, search, returning to the top level, a notepad facility, and a quit option. Local icons are provided on the individual pages as and when necessary. These provide control at the page level including page turning and picture display.

Case 2: Slide Show Metaphors on Photo CD

Photo CD is one of the latest optical disc technologies to emerge from research into new publication media (Kodak, 1991). It is targeted primarily at the mass consumer market. The idea behind Photo CD is that users are able to take photographs on their own standard 35 mm cameras and have these placed onto a compact disc. Along with the high resolution images (3000 x 2000), each compact disc also has stored on it the software necessary for Photo CD image retrieval. This software embeds an iconic interface within a 'slide show' metaphor. However, Barker argues that this application embeds two parallel metaphors - one based on a 'static picture books and the other based upon a slide show.

As with the use of metaphors in language, the use of the slide show metaphor in Photo CD is transparent. When using this technology users do not need to be consciously aware of the underlying metaphor. In this way, users are able to use the application in an 'almost' intuitive fashion - because the iconic controls are generally consistent with the metaphor.

In a traditional slide show a carousel of slides is loaded onto a slide projector. The user can then display all the slides in sequence in either direction. They may re-view the previous slide, or continue to the next slide. Slides can be removed from the slide show, or even reoriented so that they are displayed on their side or upside-down. A user determined sequence can be placed in consecutive slots in the carousel thereby providing the user with control over the order in which slides are viewed. All this functionality is mirrored in the Photo CD interface.

Many of the icons (which in this application utilise the graphic channel only) are used for the provision of facilities which are consistent with a slide projector, or slide show metaphor. Perhaps the most obvious example of consistency is the use of the standard icons which can be found on any information delivery device (for example: slide projectors; audio and video tape recorders and compact disc players). Arguably, these icons predate such delivery devices; however, the use of icons which are consistent with the icons frequently used in the environment from which the metaphor originates, assists the user in transferring ideas from an established to a new environment.

Unlike a slide show delivered from a traditional slide projector, however, in Photo CD the organisation and orientation of 'slides' is achieved using software tools rather than by the physical manipulation of the slides. In order to provide this functionality a comprehensive set of icons is provided. The design of some of these icons has arisen directly from the underlying interface metaphor. One of the best examples of the use of the metaphor in the design of this iconic interface can be seen in the icon which initiates the creation of customised slide shows. This icon literally looks like a set of slides placed one after another. When a user selects this icon the tools for selecting slides and placing them in a new presentation order become available.

In addition to the traditional features of slide shows, however, the functionality of Photo CD extends beyond the facilities provided by the underlying metaphor. Perhaps the best example of this development (beyond a slide show) is the 'zoom' facility. When a user selects this icon a white rectangle appears on the screen; this can be moved over the underlying picture using the system's pointing device. When the rectangle is anchored, the area within it is enlarged to full-screen. This provides a facility whereby a user can focus in on areas of particular interest.

Case 3: Museum Metaphors on CD-I

CD-I is a new way of using compact disc storage which overcomes many of the limitations of conventional CD-ROM. Like Photo CD, CD-I is aimed primarily at the consumer market (Philips IMS, 1992). However, unlike Photo CD, CD-I is a technology that allows the implementation of a wide range of products each of which can embed multiple metaphors. In order to illustrate this variety, two products have been chosen which illustrate two very different metaphors and styles of iconic interface. The first of these,'Treasures of the Smithsonian' is discussed in this section while the other,'Stamps: Windows on the World', is described in the following section. Details of the CD-I discs are given at the end of the reference section of the paper.

Treasures of the Smithsonian is a CD-I production which, through the use of a museum metaphor, allows users to explore the highlights of the 13 museums and the National Zoo which make up this famous American institution. The end-user interface allows users to browse through multiple subject areas and museums, explore links between objects and even 'walk around' statues.

As with many modern museums, Treasures of the Smithsonian provides a wide range of additional information in a variety of media forms. For instance, most museums provide a plaque containing textual information about each exhibit. In addition, some museums also provide audio facilities which allow visitors to access multi-lingual audio narrations which provide further information. In a similar fashion, Treasures of the Smithsonian also provides similar multiple channels of information provision.

When entering the Smithsonian, within the first two screens the user is immediately exposed to all the icon types (although not all the icons) which are used within the application. The first type of icon to be encountered is the dynamic 'mixed form' icon. When first viewed, icons in this class appear to be of the more traditional single graphic type. However, when the cursor is moved over an icon of this type it changes its form - from graphic to textual. This transition is used to provide further information about the individual function of the icon.

The second screen, which projects the myth of being in the entrance hall of the museum, uses picture icons to provide access mechanisms to the exhibits in the museum. The picons embedded in the mythical museum entrance are not made explicitly obvious to users until the screen cursor is moved into one of their areas of definition. That is, each picon appears to be just a part of the entrance hall until the cursor is moved within its physical boundary. When this happens the reactive area of the host picon then becomes highlighted, thus making it visible as an actual icon. Once again, textual augmentation takes place in order to provide further information as to the functional nature of the picon that has been selected.

One of the advantages of picons over traditional icons is their communicative power. In situations where only very few icons are required, and their size will not interfere with the working area, picons can be used to good effect. In the entrance hall of the museum the icons themselves act as a major part of the communication strategy. This means that rather than detracting from the working area, the picons form an integral part of the entrance hall myth associated with the museum metaphor.

Case 4: Book Metaphors on CD-I

The second CD-I product discussed in this paper is Stamps: Windows on the World. This electronic book provides access to information on over 300 stamps from 40 nations. The electronic medium, however, allows the information to be presented in a variety of ways including text, pictures, audio, and video stills.

In addition to a variety of presentation media, delivery from within an electronic book also allows the information to be organised and accessed in many different ways. In this 'electronic' stamp book the information is organised into five categories. These are made available through five stamp-like icons presented at the beginning of the book. Two buttons are also available on this page, one of which provides access to the introduction, whilst the other allows users to exit from the application.

The five icons at the start of the book are multiple mode icons, that is, they embed both a graphical and a textual element. The two icons labelled 'Features' and 'Collecting Tips' provide general background information about stamps and stamp collecting. Within these sections the book metaphor is reinforced by the use of a chapter style organisation of information, the use of page numbers, and a library or book-shelf backdrop.

The remaining three icons are more interesting in that they provide access to three different ways of organising information on the stamps held within the book. The icons are labelled, 'Theme View', 'World View' and 'Stamp View'. When one of these is selected an appropriate top-level 'entry menu' (consisting of picons) is presented to users. The nature of this entry menu is designed in a way that reinforces the particular access method that it represents. Within a given view, information is accessed by means of a 'standard' set of icons embedded within an 'icon bar' at the base of the screen.

An interesting feature of these icons is the implementation of two different metaphors: book and mail. The book metaphor is characterised by the index and page turning icons, whilst the mail metaphor manifests itself through a mail-box icon. This icon is interesting because it is both dynamic and culture specific (the stamp book was produced in the USA and the design makes use of a US style mail-box). As we are not so familiar with US mail-boxes, it took us (the research team) a long time before we realised what the icon represented. Even though UK culture has absorbed a great deal of US culture, particularly through the influence of mass media, the mail-box metaphor in this instance was used to design a culturally specific icon. Once it was realised that a mail-box metaphor was being used, however, its operation was consistent with our expectations of the mail-box metaphor.

The mail-box icon only becomes available when a stamp has been selected for 'close up' viewing.
Subsequently, when it is selected it toggles between open and closed. In other words, if the mail-box was closed when selected, then the act of selecting it would cause it to become open - and vice versa. Not only did the icon itself change appearance, but it also caused the central control facilities within the iconic menu bar to change both in form and in function. When the mail-box is closed the central menu bar allows browsing from stamp to stamp within a given page. Further information about a stamp can only be obtained by 'opening' the mail-box. That is, when the mail-box is open a number of additional items become available for the currently selected stamp. As many as three 'packages' can be held in the metaphorical mail-box: screen-based text; an audio narration; and (sometimes) a 'letter' containing further information -usually in the form of an audio sequence and a still video image.

Conclusions

We have spent a considerable amount of time researching and evaluating the iconic interfaces associated with a wide range of different computer based products. Primarily, our interest has been inclined towards identifying useful metaphors and examples of good practice. As a result of the substantial experience we have gained during our exploration of the relationship between icons and metaphors, we are now in a position to suggest some 'ad hoc' guidelines that summarise our findings. These are detailed in the remainder of this section.

As yet standard metaphors have not been formally identified although some 'de facto' standards are emerging. For example: desktops, electronic books, office metaphors, and so on. Because of their widespread appeal and acceptance such metaphors should, if they are acceptable, be used in situations where they are appropriate - thereby building on established knowledge.

We need sets of doff-the-shelf, tried and tested icons' which relate to particular interface metaphors. When implementing an application based upon a particular metaphor, a new interface can then incorporate these standard icons - thus allowing skills, knowledge and experience developed in one domain to be directly transferred to other application domains.

The extent of implementation of a metaphor can vary considerably. An incomplete implementation can sometimes lead to confusion, frustration and the development of poorly formed cognitive structures for an application. Metaphors should therefore be implemented to the full extent whenever this is appropriate. For example, electronic books should use the book metaphor to its fullest extent. Many so-called electronic books fail to provide even such basic aspects of the book metaphor as page numbers, headers and footers, indexes, and so on.

As we have mentioned previously, it is often convenient to employ two or more metaphors simultaneously within a given application. Of course, when using this approach it is important to ensure that the different metaphors that are used are clear and distinct from each other. Obviously, similar metaphors are likely to cause confusion in situations where they produce icons which might be equally applicable under either metaphor -especially when the functionality of the icons is different.

We believe that metaphors are important in the context of both iconic interface design and in enduser interaction. Unfortunately, when discussing the idea of interface metaphors, people sometimes make comments such as: 'As they are implicit in interfaces anyway, there is no need to be aware of them when designing iconic interfaces. 'We have already illustrated some of the kinds of problem that such an attitude can produce. We would suggest that this is a shortsighted point of view which can lead to a variety of complications and inconsistencies within the enduser interface. It is our belief, therefore, that the use of appropriate metaphors during iconic interface design can ensure that these problems are effectively circumvented.

Metaphors are tools to facilitate interface design and end-user interaction with an application. Despite their usefulness it is possible to overuse them. Overuse can lead to complicated interfaces as a result of introducing too much conceptual and cognitive complexity. It is therefore important not to use a metaphor(s) to such an extreme that it detracts from the interface usability. Indeed, we strongly recommend the identification of an optimally useful strategy when employing metaphors for iconic interface design.

Because metaphors are a 'likeness' and not 'the real thin"' they are bound to have limitations. Therefore, a metaphor will often 'break down'. It is thus imperative that a metaphor is not used or 'pushed' beyond its limitations. However, we would hope that by the time a metaphorical likeness breaks down, users will know enough about the underlying application to enable them to overcome the limitations of the metaphor.

Acknowledgements

The authors are indebted to the University of Teesside for providing facilities to enable this work to be undertaken. They also wish to express their gratitude to the UK's Science and Engineering Research Council (SERC) , A. P. Chesters & Associates, Dean Associates and the European Community's DELTA Project for financial support.

References

Barker, P.G., (1989). Basic Principles of HumanComputer Interface Design, CenturyHutchinson, London.

Barker, P.G., (1991). Electronic Books, Special Edition of Educational and Training Technology International, 28(4), 269-368.

Bogaerts, W.F. and Agema, K.S., (1992). Active Library on Corrosion, Elsevier, Amsterdam, The Netherlands.

Brown, P.J., (1986). Interactive Documentation, Software Practice and Experience,16(3),291-299.

Carroll,J.M., Mack, R.L. and Kellogg,W.A., (1988). Interface Metaphors and User Interface Design, 67-85 (Chapter 3) in Handbook of HumanComputer Interaction, (edited by M. Helander), Elsevier Science Publishers, BV, (North-Holland), Amsterdam, The Netherlands.

Erickson, T., (1990). Working With Interface Metaphors, 65-73, edited by B. Laurel, The Art of Human-Computer Interface Design, AddisonWesley Publishing Company Inc, Reading, Massachusetts, USA.

Gaver,W.W., (1989). The Sonic Finder: an Interface that uses Auditory Icons, Human-Computer Interaction, 4, 67-94.

Henderson, D.A. and Card, S.K., (1987). Rooms: The Use of Virtual Workspaces to Reduce Space Contention in a Windows-based Graphical Interface, ACM Transactions on Graphics, 5(3), 211 -243.

Lackoff, G. and Johnson, J., (1980). Metaphors We Live By, University of Chicago Press, Chicago, USA.

Manji, K.A., (1990). Pictorial Communication with Computers, PhD Thesis, Interactive Systems Research Group, School of Computing and Mathematics, University of Teesside, Cleveland, UK.

Nielson,J., (1990). Designing User Interfaces for International Use, Volume 13 in 'Advances in Human Factors/Ergonomics', Elsevier, Amsterdam, The Netherlands.

Philips IMS, (1992). Introducing CD-I, AddisonWesley Publishing Company, Wokingham, England, UK.

Richards, S.M., (1990). Guidelines for Electronic Book Production, MScThesis, Interactive Systems Research Group, School of Computing and Mathematics, University of Teesside, Cleveland, UK.

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Rubenstein, R. and Hersh, H., (1984).The Human Factor -Designing Computer Systems for People, Digital Press, Burlington, MA, USA.

Details of CD-I Products used in this Research: (1) Treasures of the Smithsonian, produced by the Smithsonian Institute, Philips CD-I Catalogue No 690-0 1 0-2.

(2) Stamps:Windows on theWorld, produced by the Smithsonian Institute, Philips CD-I Catalogue No 690-01 1-2.

Authors

Philip Barker is Professor of Applied Computing and Research Director of the Interactive Systems Research Group within the Human-Computer Interaction Laboratory at the University of Teesside. Karim Manji is a Senior Lecturer in the School of Computing and Mathematics and Ashok Banerji is a Research Assistant who is currently completing his PhD research.When the work described in this paper was originally undertaken Stephen Richards and Charles Lamont were both SERC CASE Research Students studying for their PhD awards. Currently, Stephen Richards is a Research Associate in the Department of Psychology at the University of Newcastle-upon-Tyne and Charles Lamont is a Lecturer in Computing at Cleveland College, Redcar.