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User interface standards for expert systems: Are they appropriate?
Expert Systems With Applications. Vol. 2, pp. 245-250, 1991 Printed in the USA.
0957--4174/91 $3.00 + .00 © 1991 Pergamon Press plc
User Interface Standards for Expert Systems: Are They Appropriate? D I A N N E BERRY University of Oxford, U.K.
ANNA HART Lancashire Polytechnic, Preston, U.K.
Abstract--In recent years there has been a growing debate over whether or not standards should be produced for user system interfaces. Those in favor of standardization argue that standards in this area will result in more usable systems, while those against argue that standardization is neither practical nor desirable. The present paper reviews both sides of this debate in relation to expert systems. It argues that in many areas guidelines are more appropriate than standards for user interface design.
1. I N T R O D U C T I O N
terfaces. It concludes that in many areas guideiines are more appropriate than standards for user interface design. However, particularly in the case of expert systems, much of the necessary fundamental research still has to be carried out before effective guidelines can be produced.
IN RECENT YEARS there has been a growing awareness of the importance of the user interface in expert system development (Berry & Hart, 1990). HCI issues are now often viewed as a primary consideration, rather than as a mere afterthought. Considerable research effort is being expended in this area, both in relation to expert systems and to conventional systems. It has been suggested that user interface design comprises 30-35% of operational software, and of corresponding development effort, in conventional systems. In the case of expert systems the figure will certainly not be lower. In line with the increased emphasis on the importance of the user interface, there has also been a growing debate over whether or not standards should be produced for user system interfaces. Those in favor of standardization argue that standards in this area will result in more consistent, and hence more usable, interfaces. Others, however, argue that standardization is neither practical nor desirable. This paper looks at both sides of this debate, particularly in relation to expert systems. It reviews the current work of the major standards organizations in this area, and discusses the practicality and desirability of standardizing user in-
2. T H E I M P O R T A N C E O F T H E USER INTERFACE In the early days of information systems the emphasis tended to be on the construction of a good database. After some years of experience, developers then started to emphasize the need for effective and helpful interfaces to enable users to access the databases. A similar thing has happened in the history of expert systems. Most of the early research effort went into developing different knowledge representations and inferencing procedures. Considerably less attention was paid to the user interface. In recent years, the crucial importance of the interface has become more and more apparent. One of the clearest lessons learned from the early pioneering expert systems is that excellent decisionmaking performance in itself is not sufficient to guarantee user acceptability. Users must be able to communicate effectively with the complex systems which they are supposed to use. Moreover, in some domains it is not even possible for systems to attain excellent levels of performance, and so, give authoritative advice. Clearly, in such cases the issue of effective h u m a n -
The authors are grateful to Nigel Bevan for providing material on the current activities of the various Standards Organizations. Requests for reprints should be sent to Dianne Berry, Department o f Experimental Psychology, University of Oxford, Oxford, OX 1 3UD, U.K.
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computer interaction (HCI) is of paramount importance. In order that systems can be used effectively, users must have an adequate conceptual model of what the system does, and be able to interact with it. This requires their being able to assess whether or not the system could be used to help with a particular problem, to be able to input any data correctly, to assimilate any output, and to combine system advice with their own knowledge about the problem in order to reach a conclusion. If the task being undertaken is relatively simple then the user may well be able to tolerate some problems with the system interaction; but when the task is complex, proble,ms in the input or output of information or in understanding the way the system is reacting may be ,Jeleterious. In other words, it is desirable for the system to be "natural" to use so that the user can concentrat,~. on the problem being solved rather than on "how to get the system to work." While similar issues arise for both expert systems and information systems, there are differences between. conventional systems and expert systems that have implications as far as the interface is concerned. Expert systems are often designed for assistance with quite complex problems where the information can be imprecise and unreliable. The systems themselves are unlikely to be "correct" or thoroughly testable, and in many cases the users will have to take responsibility for any action or decision, having taken into consideration the system's advice. The need for an adequate conceptual model of what the system does is clearly imperative. In many situations expert systems must be able to support brief interactions and must be able to respond flexibly to the specific and changing needs of the user. Moreover, the background, skills, and needs of expert system users will often be different from those of information system users. There have been numerous examples of expert systems being rejected by users because insufficient attention was paid to ascertaining user needs and developing a system with a corresponding functionality and an appropriate interface to match these needs (Berry & Broadbent, 1987). Kidd and Cooper (1985), for example, developed a system for fault-finding radio equipment, using an early expert system shell. The system was rejected by the user technicians because it asked too many irrelevant questions and was inflexible. There was no adequate volunteer facility and the system would not let them cut corners. Taylor (1985) reports similar problems in relation to an expert system which was developed for partial fault finding of computer terminals. Such problems still occur in industrial system development. Many researchers and practitioners are now aware of these early mistakes and considerable effort is being expended on developing improved methods of user in-
D. Berry and A. Hart
terface design in relation to both expert systems (Berry & Hart, 1990), and conventional systems (Bice & Lewis, 1989). As well as striving for technological advances and proposing development methodologies which recommend user involvement, some writers have suggested that standardization is a way of improving user interface design. The desirability of developing and imposing standards in this area is discussed next. 3. T H E DESIRABILITY O F STANDARDS The arguments which follow are made largely in relation to conventional systems. There is, however, no definite distinction between expert systems and other information systems and the trend is away from standalone systems toward integration. Expert systems technology may be relatively less mature, but in principle, any arguments about interface standards for conventional systems will apply to expert systems as well. Holdaway and Bevan (1989) list four potential benefits of user interface standards. They suggest that standards can provide consistency, enhance usability, improve comfort and well being, and assist in product procurement and evaluation. As far as consistency is concerned, it is suggested that standards can provide consistency in screen and keyboard layout, in terminology and semantics, in user action and syntax, and across and within manufacturers, systems, and applications. Many writers have stressed the importance of user interface consistency (for example, Poison, 1988; Rubinstein & Hersh, 1984; Shneiderman, 1987; and Smith & Mosier, 1986). Smith and Mosier conclude their compendium of guidelines for user interface software, in which over 60 guidelines contain the word "consistent" in the title, by stating that "the single objective on which experts agree is design consistency." The general argument in favor of consistency is that once users have learned how a system operates, it saves both time and effort if other systems work in a similar way. It would be very desirable if users could move from one system to another without having to relearn how each individual system operates. Problems due to inconsistency are certainly well documented in the HCI literature. Many users, for example, have experienced the frustration of deleting a file instead of saving it, due to the inconsistent use of function keys. Proponents of standardization have argued that laying down standards is the most effective way to achieve consistency. They claim that if all interfaces conform to certain standards then differences between systems should be minimized. Although this is undoubtedly true, it must be recognized that total consistency in interface design may be neither achievable (Kellogg, 1987), nor desirable. Grudin (1989) has recently put
User Interface Standards
forward a very coherent argument against the case for user interface consistency. The second stated benefit of standardizing the user interface is enhanced usability and, clearly, this is a vital aspect in relation to any computer system. Within the HCI literature there is a debate over an acceptable definition of the term "usability." The definition currently used by the International Standards Organization's subgroup working in this area is "the usability of a product is defined operationally as the degree to which specific users can achieve specified goals in a particular environment, effectively, efficiently, comfortably and in an acceptable manner." Hence, the usability of a system depends on who is using the system, what they are using it for, and the conditions under which it is being used. Again, those in favor of standardization argue that conformance to standards should result in systems that are more usable and effective. It is claimed that higher quality user interfaces will result from adherence to standards designed to maximize usability. Simply developing standards per se, however, will not necessarily guarantee enhanced usability. As pointed out below, current research is still limited and the dimensions of usability are not well understood. We are far from certain what makes one interface more usable than another; standardizing on the wrong aspects could lead to diminished usability. As far as comfort and well being are concerned, there has been pressure from user groups for standards and laws to protect users. Some of these relate to specific health problems, but there is also a more general fear that a poorly constructed user interface will cause stress and mental anguish to the end user. Again, many believe that standards for user interfaces will ensure that users are free from interface-related health and well being problems. It has been argued, for example, that standards will ensure that the user remains in control in interactions and is not subjected to undesirable system imposed time pressures. Similarly, it has been argued that they will reduce other causes of stress, such as the fear of making mistakes. Finally, there is an increasing belief that user interface standards will be of significant benefit when comparing and purchasing systems. At present different user interfaces are difficult to specify, assess, or compare. By specifying that the product must conform to a certain standard, the buyer could ensure that the system will provide a nominal level of consistency and usability. Moreover, it is argued that if a new product has a "standard interface" employees may be less worried about health and well being. In general, there are several arguments in favor of introducing user interface standards which apply to all types of computer systems. There is also pressure from certain user groups to implement standards. Accordingly, several national and international standards or-
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ganizations are developing standards for the user interface. 4. C U R R E N T STANDARDS ACTIVITIES Within the last decade several standards-producing organizations have turned their attention to the user system interface. As yet, their discussions and outputs have been in relation to computer systems in general, rather than specifically to expert systems. This is not a problem, however, as the particular topics covered tend to be those that are c o m m o n to both conventional and expert systems. Moreover, as discussed below, the features that are more specific to expert systems may not at present, or in the foreseeable future, be amenable to standardization. The initial focus of interest of the standards organizations was on hardware ergonomics, and several standards for this area have been produced (see Abernethy, 1988, for a review). More recently, interest has centered on what Abernethy terms "software ergonomics," and several international and national standards groups are developing standards for the user interface. The activities of the major groups working on this topic are described below (see Abernethy, 1988; Billingsley, 1989; and Holdaway & Bevan, 1989 for more comprehensive reviews).
4.1. ISO TCI59/SC4/WG5: Software Ergonomics and Man Machine Dialogue Technical committee 159 (TC 159) of the International Organization for Standardization (ISO) is responsible for developing standards in the area of ergonomics. Subcommittee 4 (SC4) is working in the area of signal and controls in relation to visual display terminals. There are various working groups within SC4, some of which are concerned with hardware issues. In 1985, working group 5 (WG5) was set up to look at the ergonomics of software. The scope of WG5 is "standardization in the field of human-computer interaction, especially dialogue interfaces, with the aim of enabling users to perform their tasks under ergonomically favorable conditions." To focus their efforts, they are primarily concentrating on activities found in the office environment. Most of the work so far has been in the areas of dialogue interface and software usability. As far as dialogue interface standards are concerned, the objective is to produce standards that facilitate both interface quality and uniformity. The aim is to improve the usability of the user interfaces of all systems and to decrease the differences between user interfaces within and between systems. The objective of the software usability group is to provide a standard which specifies the content of a usability assurance statement. This will contain a statement of what procedures a manu-
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facturer has adopted to assure the usability of a product for particular tasks and groups of users. It can also include the results of an experimental validation of the usability of the product. 4.2. I S O / I E C J T C I / S C 1 8 / W G 9 : User System
Interfaces and Symbols Joint Technical Committee One (JTCI) of ISO/International Electrotechnical Commission (IEC) has responsibility for standards in the area of information technology. Subcommittee 18 (SC18) is responsible for developing standards in the area of text and ottice systems. Within this subcommittee, working group 9 (WG9) is responsible for user system interfaces. The three principal areas being addressed by this working group are keyboard layout, user interface (dialogue interaction), and symbols. The work on keyboards consists of developing a multipart standard that will update, extend, and replace existing standards for keyboard layout. The work of the user interface group covers dialogue techniques, user guidance, and the names of objects and actions c o m m o n in office systems. The symbols group is working on graphic symbols used on equipment such as printer control panels. The latter two groups are also jointly working on symbols used in screen menus. In addition to these two international groups, various national groups are also active in this area. Within the U.S., for example, the H u m a n Factors SocietyHuman Computer Interaction Committee (HFS-HCI) operates under the auspices of the American National Standards Institute (ANSI). Their primary task has been to produce guidelines (which may then be made into standards) in the areas of dialogue interaction techniques, user guidance, and output devices and techniques. Similarly, P1201 is chartered by the IEEE to develop standards that facilitate application and portability in X window-based environments. Within West Germany the Deutsches Institut fiir Normung (DIN) is working in the area of ergonomic dialogue design. Other national bodies are active in France, Sweden, and the U.K. 5. T H E CASE AGAINST STANDARDS Despite the arguments in favor of standards, and the efforts of the various standards organizations, not everyone believes that standardization is a good thing. The principal argument against user interface standards is that there is still a lot to learn about what makes a good user interface. The level of expertise in user interface design does not match the level of precision and rigor required by standards. Much of the relevant research, particularly that on human cognitive processes, has not been carried out. As Landauer (1987) states, at present "there are far too many holes, and too many uncertainties in what principles are relevant
to what tasks." If standards are based on opinion, rather than on a sound body of facts and experimental results, problems are bound to arise. One could argue that this criticism is less valid in the case of hardware ergonomics where more of the basics are known. Smith (1986), for example, has suggested that hardware is more amenable than software to standardization as it is based on physiology, which is considered to be relatively fixed, measured, and understood. Despite this, there have been some criticisms of the way in which hardware standards have been introduced. Abernethy (1988), for example, argues that the technical basis for many existing hardware standards rests on a very uneven scientific foundation. He cites a study by Hellander, Billingsley, and Schurick (1982) which reviews 64 original studies and concludes that each is flawed in one or more aspect of experimental design and analysis. Another criticism which is voiced against standardization is that standards will inhibit technological advances. It is argued that if current interfaces are less than optimal then standardization will simply doom us to inferior interfaces for years to come. As McDonald and Schvaneveldt (1988) point out, "it would be foolish to insist on consistent interface design before learning about good interface design." Standards imply stability and repeatability, but it is necessary to question whether this is a good thing in an area where technology and innovation are expanding dramatically. Standardizing on what is c o m m o n today could prevent the innovative new interfaces of tomorrow. For example, if standards had been laid down 5 or more years ago when systems typically had character-based, command line, scrolling interfaces this may have preempted many features of current object-oriented interfaces. Similarly, if standards are laid down now, who knows what new advances will be preempted? Finally, it can be argued that many standards will not necessarily provide measurable benefits for either the designer or the user. In the case of designers, conformance to standards may actually increase their burden, forcing them to consull large collections of recommendations. The standards may be conflicting, difficult to use (Rogers & Pegden, 1977), and not relevant to particular applications (Hirsch, 1984). Designers may regard standards as either a restrictive hindrance or a useless formality, depending on the degree to which the standards are reinforced. In the case of users, it is difficult to see how some of the standards being discussed at present could have any measurable benefit. Without such benefit, however, standardization will simply result in rigid, inflexible interfaces that cannot accommodate a broad range of users, tasks, and environments. It is clear from the above arguments that it is necessary to consider who standards are aimed at, what specific benefits they should bring, and what is their
User Interface Standards
intended scope and coverage. It should be noted, for example, that although the above criticisms may argue against the use of universally applied standards, they would not necessarily rule out the use of certain inhouse human factors standards. Where standards are introduced, methods of testing and certification need to be decided on and issues of responsibility considered. It is also necessary to think about the appropriate form that any standards should take. Holdaway and Bevan (1989) suggest that we can avoid some of the potential dangers of standardization by finding alternatives to the conventional style of information technology standard, which places explicit requirements on hardware and software. They state that other types of standards, which might be more appropriate when dealing with human behavior, could specify procedures (such as the procedure an organization follows to ensure the quality of a product), or minimum levels of user performance with a product, or the method by which characteristics are measured. Similarly, Smith (1986) has argued that it is the process of design, rather than the product, that is amenable to standardization. He suggests that it is the process of establishing design rules that should be imposed, rather than the rules themselves. 6. ARE GUIDELINES MORE APPROPRIATE?
Standards are by nature specific, prescriptive, and authoritative, and presuppose a thorough understanding of the areas that they address. For interface design, the relevant areas include hardware ergonomics, and both the physical and cognitive aspects of software ergonomics. At present, standardization is infeasible for the more cognitive aspects, where our understanding is far from adequate. This is especially important in knowledge engineering where expert systems can be designed to assist with decision-making tasks that require judgement and that involve uncertain or imprecise information. For these types of application, interfaces may need iterative development taking into account specific tasks, users, and intended environments. Currently, therefore, it would be unwise to try to produce standards covering all aspects of interfaces to expert systems. Where standards can not be drawn up, guidelines may be helpful. In fact, some writers have suggested that guidelines are more appropriate for user interface design in general. Smith (1986), for example, argued that our knowledge supports the development of design guidelines for user interface software, but does not justify the imposition of standards. In making the distinction, he defined standards as a series of generally stated requirements for user interface design, imposed in some formal way, such as by legislation, contract, or management decree, and published in official documents. In contrast, he defined guidelines as a series
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of generally stated recommendations for user interface software, with examples, added explanation, and other commentary, selected for any particular system application, and adopted by agreement among people concerned with interface design. Smith argued that guidelines offer a more flexible and detailed kind of guidance which helps to focus attention on user interface design and the establishment of agreed design objectives. He suggested that they also permit flexible adaptation as knowledge in the area grows, whereas standards are hard to change once established. Although guidelines for user interface design are in many respects more appropriate than standards, it is not necessarily the case that adherence to guidelines will improve interface design. One problem is that although guidelines offer potentially good advice they may be too general to be applied directly. There is a conflict between the need to phrase guidelines generally for broad application and the designer's need for specific rules. Guidelines may be of little use to the front line designer unless they can be translated into specific design rules, that is, into a series of explicit software design specifications for a particular system application. It is also the case that the use of guidelines may not save work for the designer and may rather create more work. Smith (1986) carried out a survey of 130 designers and human factors specialists. He found that guidelines were considered to be generally useful for establishing requirements in advance of design, as a decision aid, and for evaluation purposes. However, various shortcomings were also noted. First, respondents could not always find the relevant information even when it was present. Second, guidelines were sometimes seen as being irrelevant, either too general or too specific. Third, the respondents sometimes had difficulty in determining tradeoffs among conflicting guidelines. Finally, some respondents noted difficulties where new technology was concerned as the guidelines tended to lag behind the times. Some of these criticisms may only apply to the specific guidelines that were consulted by the respondents. The number of sets of guidelines being produced is on the increase and designers must choose which are the most appropriate for their needs. There may be considerable overlap in their content, but there will also be major inconsistencies. Guidelines should be based on established principles and experimental results, rather than on informed opinion. In order to confirm this, designers should check that the guidelines state their source and method of derivation. A good example of this process is given by Marshall, Nelson, and Gardiner (1987). There may also be differences in the areas covered by the guidelines. Many existing collections focus very much on individual screen layouts, rather than on the interaction as a whole. One could, however, readily
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envision a situation where each individual screen display met the appropriate standards, but the interaction as a whole was still unacceptable to users. Designers must, therefore, not be lulled into a false sense of security simply because individual screens are in line with guidelines. In general, the more complex the interface the less plausible it is that guidelines will help. Guidelines are necessarily incomplete and require evaluation and interpretation by the designer. Nonetheless, they can provide a framework within which advice on certain aspects of interface design can be obtained. 7. CONCLUSION Standardization may be appropriate for certain aspects of user interface design, such as those concerning hardware ergonomics and the more physical aspects of software ergonomics. Many areas, however, particularly those concerned with higher level cognitive functions, are not amenable to standardization. Acceptance of standards assumes that due consideration has been given to most, if not all, types of users, tasks, and problem-solving environments, and that the salient features of each have been understood. The trend within expert systems, however, is towards quite diverse applications with many classes of users and environments, which implies that such a complete understanding is not available at present. This does not mean, however, that expert system designers should be left without help or advice. Carefully designed experiments can yield useful generalizations about expert system interfaces. Designers should not be expected to sift through reports of these experiments in order to find results that are relevant to them. Guidelines, although incomplete and despite their disadvantages, can be used to disseminate such experience and findings. A comparison can be made with system development methodologies. Very few people follow methodologies to the letter but most acknowledge the rationale behind them, benefit from them, and in effect learn when to break the rules or tailor them to their own requirements. Guidelines can perform a similar function in interface design. As stated above, however, they must be accompanied by details of their intended application, source, and method of derivation. It is unlikely that such guidelines will translate directly into design rules. In order to use them effectively the designer must be able to interpret and apply them, both sensitively and intelligently. Guidelines cannot, therefore, take the place of experience and designers should not be encouraged to believe that by following guidelines they can be guaranteed to produce optimal designs. Given the complexity of the problem, guidelines can only address certain aspects of interface design. Areas such as adaptive dialogues, explanation facilities, and multimedia in-
teraction still require far more research before we can even think about producing effective guidelines. Clearly, the expert systems community will benefit from guidelines in those areas that have been well researched. While it may be practical to produce such guidelines, it is currently infeasible to aim for comprehensive standards. REFERENCES Abernethy, C.N. (1988). Human-computer interface standards: Origins, organizations and comment. International Reviews of Ergonomics, 2, 31-54. Berry, D.C., & Hart, A.E. (1990). Expert systems: Human issues. London: Chapman and Hall. Berry, D.C., & Broadbent, D.E. (1987). The user interface. Expert
Systems: The International Journal of Knowledge Engineering, 4, 18-27. Bice, K., & Lewis, C. (Eds.). (1989). Human factors in computing systems: Proceedings of CHl 89. New York: ACM Press. Billingsley, P. (1989). The standards factor. SIGCHI Bulletin, 21, 13-16. Grudin, J. (1989). The case against user interface consistency. Communications of the ACM, 32, 1165-1173. Helander, M.G., Billingsley, P.A., & Schurick, J.M. (1982). A critical review of human factors research of visual display terminals (Report No. CRG-TR-82-004). Morristown, NJ: Bell Labs. Hirsch, R.S. (1984). VDTs and the human factors community. Tipping the iceberg. Human Factors Society Bulletin, 27, 1-3. Holdaway, K., & Bevan, N. (1989). User system interaction Standards. Computer Communications, 12, 97-102. Kellogg, W.A. (1987). Conceptual consistency in the user interface. Effects on user performance. In H. J. Bullinger, B. Shackel, & K. Kornwachs (Eds.), Proceedings of INTERACT '87 Conference on Human-Computer Interaction (pp. 389-395). Amsterdam: North Holland. Kidd, A., & Cooper, M.B. (1985). Man-machine interface issues in the construction and use of an expert system. International Journal of Man-Machine Studies, 22, 91-102. Landauer, T.K. (1987). Relations between cognitived psychology and computer system design. In J.M. Carroll (Ed.), Interfacing thought. Cambridge, MA: MIT Press. McDonald, J.E., & Schvaneveldt, R.W. (1988). The application of user knowledge to interface design. In R. Guindon (Ed.), Cognitive
science and its applications for human-computer interaction. Hillsdale, N J: Lawrence Erlbaum. Marshall, C., Nelson, C., & Gardiner, M. (1987). Design guidelines. In M. Gardiner & B. Christie (Eds.), Applying cognitive psychology to user interface design. Chichester, U.K.: Wiley. Poison, P. (1988). The consequences of consistent and inconsistent user interfaces. In R. Guindon (Ed.), Cognitive science and its applications for human-computer interaction. Hillsdale, N J: Lawrence Erlbaum. Rogers, J.G., & Pegden, C.D. (1977). Formatting and organization of a human engineering standard. Human Factors, 19, 55-66. Rubinstein, R., & Hersh, H. (1984). The human factor. Bedford, MA: Digital Press. Shneiderman, B. (1987). Designing the user interface. Reading, MA: Addison-Wesley. Smith, S.L. (1986). Standards versus guidelines for designing user interface software. Behaviour and Information Technology, 5, 4761. Smith, S.L., & Mosier, J.N. (1986). GuidelinesJor designing user interface software (Report 7 MTR-10090, Esd-Tr-86-278). Bedford, MA: MITRE Corporation. Taylor, J.M. (1985). An expert system for terminal fault diagnosis.
Proceedings of the First International Expert Systems Conference on Learned Information. Oxford.
0957--4174/91 $3.00 + .00 © 1991 Pergamon Press plc
User Interface Standards for Expert Systems: Are They Appropriate? D I A N N E BERRY University of Oxford, U.K.
ANNA HART Lancashire Polytechnic, Preston, U.K.
Abstract--In recent years there has been a growing debate over whether or not standards should be produced for user system interfaces. Those in favor of standardization argue that standards in this area will result in more usable systems, while those against argue that standardization is neither practical nor desirable. The present paper reviews both sides of this debate in relation to expert systems. It argues that in many areas guidelines are more appropriate than standards for user interface design.
1. I N T R O D U C T I O N
terfaces. It concludes that in many areas guideiines are more appropriate than standards for user interface design. However, particularly in the case of expert systems, much of the necessary fundamental research still has to be carried out before effective guidelines can be produced.
IN RECENT YEARS there has been a growing awareness of the importance of the user interface in expert system development (Berry & Hart, 1990). HCI issues are now often viewed as a primary consideration, rather than as a mere afterthought. Considerable research effort is being expended in this area, both in relation to expert systems and to conventional systems. It has been suggested that user interface design comprises 30-35% of operational software, and of corresponding development effort, in conventional systems. In the case of expert systems the figure will certainly not be lower. In line with the increased emphasis on the importance of the user interface, there has also been a growing debate over whether or not standards should be produced for user system interfaces. Those in favor of standardization argue that standards in this area will result in more consistent, and hence more usable, interfaces. Others, however, argue that standardization is neither practical nor desirable. This paper looks at both sides of this debate, particularly in relation to expert systems. It reviews the current work of the major standards organizations in this area, and discusses the practicality and desirability of standardizing user in-
2. T H E I M P O R T A N C E O F T H E USER INTERFACE In the early days of information systems the emphasis tended to be on the construction of a good database. After some years of experience, developers then started to emphasize the need for effective and helpful interfaces to enable users to access the databases. A similar thing has happened in the history of expert systems. Most of the early research effort went into developing different knowledge representations and inferencing procedures. Considerably less attention was paid to the user interface. In recent years, the crucial importance of the interface has become more and more apparent. One of the clearest lessons learned from the early pioneering expert systems is that excellent decisionmaking performance in itself is not sufficient to guarantee user acceptability. Users must be able to communicate effectively with the complex systems which they are supposed to use. Moreover, in some domains it is not even possible for systems to attain excellent levels of performance, and so, give authoritative advice. Clearly, in such cases the issue of effective h u m a n -
The authors are grateful to Nigel Bevan for providing material on the current activities of the various Standards Organizations. Requests for reprints should be sent to Dianne Berry, Department o f Experimental Psychology, University of Oxford, Oxford, OX 1 3UD, U.K.
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computer interaction (HCI) is of paramount importance. In order that systems can be used effectively, users must have an adequate conceptual model of what the system does, and be able to interact with it. This requires their being able to assess whether or not the system could be used to help with a particular problem, to be able to input any data correctly, to assimilate any output, and to combine system advice with their own knowledge about the problem in order to reach a conclusion. If the task being undertaken is relatively simple then the user may well be able to tolerate some problems with the system interaction; but when the task is complex, proble,ms in the input or output of information or in understanding the way the system is reacting may be ,Jeleterious. In other words, it is desirable for the system to be "natural" to use so that the user can concentrat,~. on the problem being solved rather than on "how to get the system to work." While similar issues arise for both expert systems and information systems, there are differences between. conventional systems and expert systems that have implications as far as the interface is concerned. Expert systems are often designed for assistance with quite complex problems where the information can be imprecise and unreliable. The systems themselves are unlikely to be "correct" or thoroughly testable, and in many cases the users will have to take responsibility for any action or decision, having taken into consideration the system's advice. The need for an adequate conceptual model of what the system does is clearly imperative. In many situations expert systems must be able to support brief interactions and must be able to respond flexibly to the specific and changing needs of the user. Moreover, the background, skills, and needs of expert system users will often be different from those of information system users. There have been numerous examples of expert systems being rejected by users because insufficient attention was paid to ascertaining user needs and developing a system with a corresponding functionality and an appropriate interface to match these needs (Berry & Broadbent, 1987). Kidd and Cooper (1985), for example, developed a system for fault-finding radio equipment, using an early expert system shell. The system was rejected by the user technicians because it asked too many irrelevant questions and was inflexible. There was no adequate volunteer facility and the system would not let them cut corners. Taylor (1985) reports similar problems in relation to an expert system which was developed for partial fault finding of computer terminals. Such problems still occur in industrial system development. Many researchers and practitioners are now aware of these early mistakes and considerable effort is being expended on developing improved methods of user in-
D. Berry and A. Hart
terface design in relation to both expert systems (Berry & Hart, 1990), and conventional systems (Bice & Lewis, 1989). As well as striving for technological advances and proposing development methodologies which recommend user involvement, some writers have suggested that standardization is a way of improving user interface design. The desirability of developing and imposing standards in this area is discussed next. 3. T H E DESIRABILITY O F STANDARDS The arguments which follow are made largely in relation to conventional systems. There is, however, no definite distinction between expert systems and other information systems and the trend is away from standalone systems toward integration. Expert systems technology may be relatively less mature, but in principle, any arguments about interface standards for conventional systems will apply to expert systems as well. Holdaway and Bevan (1989) list four potential benefits of user interface standards. They suggest that standards can provide consistency, enhance usability, improve comfort and well being, and assist in product procurement and evaluation. As far as consistency is concerned, it is suggested that standards can provide consistency in screen and keyboard layout, in terminology and semantics, in user action and syntax, and across and within manufacturers, systems, and applications. Many writers have stressed the importance of user interface consistency (for example, Poison, 1988; Rubinstein & Hersh, 1984; Shneiderman, 1987; and Smith & Mosier, 1986). Smith and Mosier conclude their compendium of guidelines for user interface software, in which over 60 guidelines contain the word "consistent" in the title, by stating that "the single objective on which experts agree is design consistency." The general argument in favor of consistency is that once users have learned how a system operates, it saves both time and effort if other systems work in a similar way. It would be very desirable if users could move from one system to another without having to relearn how each individual system operates. Problems due to inconsistency are certainly well documented in the HCI literature. Many users, for example, have experienced the frustration of deleting a file instead of saving it, due to the inconsistent use of function keys. Proponents of standardization have argued that laying down standards is the most effective way to achieve consistency. They claim that if all interfaces conform to certain standards then differences between systems should be minimized. Although this is undoubtedly true, it must be recognized that total consistency in interface design may be neither achievable (Kellogg, 1987), nor desirable. Grudin (1989) has recently put
User Interface Standards
forward a very coherent argument against the case for user interface consistency. The second stated benefit of standardizing the user interface is enhanced usability and, clearly, this is a vital aspect in relation to any computer system. Within the HCI literature there is a debate over an acceptable definition of the term "usability." The definition currently used by the International Standards Organization's subgroup working in this area is "the usability of a product is defined operationally as the degree to which specific users can achieve specified goals in a particular environment, effectively, efficiently, comfortably and in an acceptable manner." Hence, the usability of a system depends on who is using the system, what they are using it for, and the conditions under which it is being used. Again, those in favor of standardization argue that conformance to standards should result in systems that are more usable and effective. It is claimed that higher quality user interfaces will result from adherence to standards designed to maximize usability. Simply developing standards per se, however, will not necessarily guarantee enhanced usability. As pointed out below, current research is still limited and the dimensions of usability are not well understood. We are far from certain what makes one interface more usable than another; standardizing on the wrong aspects could lead to diminished usability. As far as comfort and well being are concerned, there has been pressure from user groups for standards and laws to protect users. Some of these relate to specific health problems, but there is also a more general fear that a poorly constructed user interface will cause stress and mental anguish to the end user. Again, many believe that standards for user interfaces will ensure that users are free from interface-related health and well being problems. It has been argued, for example, that standards will ensure that the user remains in control in interactions and is not subjected to undesirable system imposed time pressures. Similarly, it has been argued that they will reduce other causes of stress, such as the fear of making mistakes. Finally, there is an increasing belief that user interface standards will be of significant benefit when comparing and purchasing systems. At present different user interfaces are difficult to specify, assess, or compare. By specifying that the product must conform to a certain standard, the buyer could ensure that the system will provide a nominal level of consistency and usability. Moreover, it is argued that if a new product has a "standard interface" employees may be less worried about health and well being. In general, there are several arguments in favor of introducing user interface standards which apply to all types of computer systems. There is also pressure from certain user groups to implement standards. Accordingly, several national and international standards or-
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ganizations are developing standards for the user interface. 4. C U R R E N T STANDARDS ACTIVITIES Within the last decade several standards-producing organizations have turned their attention to the user system interface. As yet, their discussions and outputs have been in relation to computer systems in general, rather than specifically to expert systems. This is not a problem, however, as the particular topics covered tend to be those that are c o m m o n to both conventional and expert systems. Moreover, as discussed below, the features that are more specific to expert systems may not at present, or in the foreseeable future, be amenable to standardization. The initial focus of interest of the standards organizations was on hardware ergonomics, and several standards for this area have been produced (see Abernethy, 1988, for a review). More recently, interest has centered on what Abernethy terms "software ergonomics," and several international and national standards groups are developing standards for the user interface. The activities of the major groups working on this topic are described below (see Abernethy, 1988; Billingsley, 1989; and Holdaway & Bevan, 1989 for more comprehensive reviews).
4.1. ISO TCI59/SC4/WG5: Software Ergonomics and Man Machine Dialogue Technical committee 159 (TC 159) of the International Organization for Standardization (ISO) is responsible for developing standards in the area of ergonomics. Subcommittee 4 (SC4) is working in the area of signal and controls in relation to visual display terminals. There are various working groups within SC4, some of which are concerned with hardware issues. In 1985, working group 5 (WG5) was set up to look at the ergonomics of software. The scope of WG5 is "standardization in the field of human-computer interaction, especially dialogue interfaces, with the aim of enabling users to perform their tasks under ergonomically favorable conditions." To focus their efforts, they are primarily concentrating on activities found in the office environment. Most of the work so far has been in the areas of dialogue interface and software usability. As far as dialogue interface standards are concerned, the objective is to produce standards that facilitate both interface quality and uniformity. The aim is to improve the usability of the user interfaces of all systems and to decrease the differences between user interfaces within and between systems. The objective of the software usability group is to provide a standard which specifies the content of a usability assurance statement. This will contain a statement of what procedures a manu-
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facturer has adopted to assure the usability of a product for particular tasks and groups of users. It can also include the results of an experimental validation of the usability of the product. 4.2. I S O / I E C J T C I / S C 1 8 / W G 9 : User System
Interfaces and Symbols Joint Technical Committee One (JTCI) of ISO/International Electrotechnical Commission (IEC) has responsibility for standards in the area of information technology. Subcommittee 18 (SC18) is responsible for developing standards in the area of text and ottice systems. Within this subcommittee, working group 9 (WG9) is responsible for user system interfaces. The three principal areas being addressed by this working group are keyboard layout, user interface (dialogue interaction), and symbols. The work on keyboards consists of developing a multipart standard that will update, extend, and replace existing standards for keyboard layout. The work of the user interface group covers dialogue techniques, user guidance, and the names of objects and actions c o m m o n in office systems. The symbols group is working on graphic symbols used on equipment such as printer control panels. The latter two groups are also jointly working on symbols used in screen menus. In addition to these two international groups, various national groups are also active in this area. Within the U.S., for example, the H u m a n Factors SocietyHuman Computer Interaction Committee (HFS-HCI) operates under the auspices of the American National Standards Institute (ANSI). Their primary task has been to produce guidelines (which may then be made into standards) in the areas of dialogue interaction techniques, user guidance, and output devices and techniques. Similarly, P1201 is chartered by the IEEE to develop standards that facilitate application and portability in X window-based environments. Within West Germany the Deutsches Institut fiir Normung (DIN) is working in the area of ergonomic dialogue design. Other national bodies are active in France, Sweden, and the U.K. 5. T H E CASE AGAINST STANDARDS Despite the arguments in favor of standards, and the efforts of the various standards organizations, not everyone believes that standardization is a good thing. The principal argument against user interface standards is that there is still a lot to learn about what makes a good user interface. The level of expertise in user interface design does not match the level of precision and rigor required by standards. Much of the relevant research, particularly that on human cognitive processes, has not been carried out. As Landauer (1987) states, at present "there are far too many holes, and too many uncertainties in what principles are relevant
to what tasks." If standards are based on opinion, rather than on a sound body of facts and experimental results, problems are bound to arise. One could argue that this criticism is less valid in the case of hardware ergonomics where more of the basics are known. Smith (1986), for example, has suggested that hardware is more amenable than software to standardization as it is based on physiology, which is considered to be relatively fixed, measured, and understood. Despite this, there have been some criticisms of the way in which hardware standards have been introduced. Abernethy (1988), for example, argues that the technical basis for many existing hardware standards rests on a very uneven scientific foundation. He cites a study by Hellander, Billingsley, and Schurick (1982) which reviews 64 original studies and concludes that each is flawed in one or more aspect of experimental design and analysis. Another criticism which is voiced against standardization is that standards will inhibit technological advances. It is argued that if current interfaces are less than optimal then standardization will simply doom us to inferior interfaces for years to come. As McDonald and Schvaneveldt (1988) point out, "it would be foolish to insist on consistent interface design before learning about good interface design." Standards imply stability and repeatability, but it is necessary to question whether this is a good thing in an area where technology and innovation are expanding dramatically. Standardizing on what is c o m m o n today could prevent the innovative new interfaces of tomorrow. For example, if standards had been laid down 5 or more years ago when systems typically had character-based, command line, scrolling interfaces this may have preempted many features of current object-oriented interfaces. Similarly, if standards are laid down now, who knows what new advances will be preempted? Finally, it can be argued that many standards will not necessarily provide measurable benefits for either the designer or the user. In the case of designers, conformance to standards may actually increase their burden, forcing them to consull large collections of recommendations. The standards may be conflicting, difficult to use (Rogers & Pegden, 1977), and not relevant to particular applications (Hirsch, 1984). Designers may regard standards as either a restrictive hindrance or a useless formality, depending on the degree to which the standards are reinforced. In the case of users, it is difficult to see how some of the standards being discussed at present could have any measurable benefit. Without such benefit, however, standardization will simply result in rigid, inflexible interfaces that cannot accommodate a broad range of users, tasks, and environments. It is clear from the above arguments that it is necessary to consider who standards are aimed at, what specific benefits they should bring, and what is their
User Interface Standards
intended scope and coverage. It should be noted, for example, that although the above criticisms may argue against the use of universally applied standards, they would not necessarily rule out the use of certain inhouse human factors standards. Where standards are introduced, methods of testing and certification need to be decided on and issues of responsibility considered. It is also necessary to think about the appropriate form that any standards should take. Holdaway and Bevan (1989) suggest that we can avoid some of the potential dangers of standardization by finding alternatives to the conventional style of information technology standard, which places explicit requirements on hardware and software. They state that other types of standards, which might be more appropriate when dealing with human behavior, could specify procedures (such as the procedure an organization follows to ensure the quality of a product), or minimum levels of user performance with a product, or the method by which characteristics are measured. Similarly, Smith (1986) has argued that it is the process of design, rather than the product, that is amenable to standardization. He suggests that it is the process of establishing design rules that should be imposed, rather than the rules themselves. 6. ARE GUIDELINES MORE APPROPRIATE?
Standards are by nature specific, prescriptive, and authoritative, and presuppose a thorough understanding of the areas that they address. For interface design, the relevant areas include hardware ergonomics, and both the physical and cognitive aspects of software ergonomics. At present, standardization is infeasible for the more cognitive aspects, where our understanding is far from adequate. This is especially important in knowledge engineering where expert systems can be designed to assist with decision-making tasks that require judgement and that involve uncertain or imprecise information. For these types of application, interfaces may need iterative development taking into account specific tasks, users, and intended environments. Currently, therefore, it would be unwise to try to produce standards covering all aspects of interfaces to expert systems. Where standards can not be drawn up, guidelines may be helpful. In fact, some writers have suggested that guidelines are more appropriate for user interface design in general. Smith (1986), for example, argued that our knowledge supports the development of design guidelines for user interface software, but does not justify the imposition of standards. In making the distinction, he defined standards as a series of generally stated requirements for user interface design, imposed in some formal way, such as by legislation, contract, or management decree, and published in official documents. In contrast, he defined guidelines as a series
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of generally stated recommendations for user interface software, with examples, added explanation, and other commentary, selected for any particular system application, and adopted by agreement among people concerned with interface design. Smith argued that guidelines offer a more flexible and detailed kind of guidance which helps to focus attention on user interface design and the establishment of agreed design objectives. He suggested that they also permit flexible adaptation as knowledge in the area grows, whereas standards are hard to change once established. Although guidelines for user interface design are in many respects more appropriate than standards, it is not necessarily the case that adherence to guidelines will improve interface design. One problem is that although guidelines offer potentially good advice they may be too general to be applied directly. There is a conflict between the need to phrase guidelines generally for broad application and the designer's need for specific rules. Guidelines may be of little use to the front line designer unless they can be translated into specific design rules, that is, into a series of explicit software design specifications for a particular system application. It is also the case that the use of guidelines may not save work for the designer and may rather create more work. Smith (1986) carried out a survey of 130 designers and human factors specialists. He found that guidelines were considered to be generally useful for establishing requirements in advance of design, as a decision aid, and for evaluation purposes. However, various shortcomings were also noted. First, respondents could not always find the relevant information even when it was present. Second, guidelines were sometimes seen as being irrelevant, either too general or too specific. Third, the respondents sometimes had difficulty in determining tradeoffs among conflicting guidelines. Finally, some respondents noted difficulties where new technology was concerned as the guidelines tended to lag behind the times. Some of these criticisms may only apply to the specific guidelines that were consulted by the respondents. The number of sets of guidelines being produced is on the increase and designers must choose which are the most appropriate for their needs. There may be considerable overlap in their content, but there will also be major inconsistencies. Guidelines should be based on established principles and experimental results, rather than on informed opinion. In order to confirm this, designers should check that the guidelines state their source and method of derivation. A good example of this process is given by Marshall, Nelson, and Gardiner (1987). There may also be differences in the areas covered by the guidelines. Many existing collections focus very much on individual screen layouts, rather than on the interaction as a whole. One could, however, readily
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envision a situation where each individual screen display met the appropriate standards, but the interaction as a whole was still unacceptable to users. Designers must, therefore, not be lulled into a false sense of security simply because individual screens are in line with guidelines. In general, the more complex the interface the less plausible it is that guidelines will help. Guidelines are necessarily incomplete and require evaluation and interpretation by the designer. Nonetheless, they can provide a framework within which advice on certain aspects of interface design can be obtained. 7. CONCLUSION Standardization may be appropriate for certain aspects of user interface design, such as those concerning hardware ergonomics and the more physical aspects of software ergonomics. Many areas, however, particularly those concerned with higher level cognitive functions, are not amenable to standardization. Acceptance of standards assumes that due consideration has been given to most, if not all, types of users, tasks, and problem-solving environments, and that the salient features of each have been understood. The trend within expert systems, however, is towards quite diverse applications with many classes of users and environments, which implies that such a complete understanding is not available at present. This does not mean, however, that expert system designers should be left without help or advice. Carefully designed experiments can yield useful generalizations about expert system interfaces. Designers should not be expected to sift through reports of these experiments in order to find results that are relevant to them. Guidelines, although incomplete and despite their disadvantages, can be used to disseminate such experience and findings. A comparison can be made with system development methodologies. Very few people follow methodologies to the letter but most acknowledge the rationale behind them, benefit from them, and in effect learn when to break the rules or tailor them to their own requirements. Guidelines can perform a similar function in interface design. As stated above, however, they must be accompanied by details of their intended application, source, and method of derivation. It is unlikely that such guidelines will translate directly into design rules. In order to use them effectively the designer must be able to interpret and apply them, both sensitively and intelligently. Guidelines cannot, therefore, take the place of experience and designers should not be encouraged to believe that by following guidelines they can be guaranteed to produce optimal designs. Given the complexity of the problem, guidelines can only address certain aspects of interface design. Areas such as adaptive dialogues, explanation facilities, and multimedia in-
teraction still require far more research before we can even think about producing effective guidelines. Clearly, the expert systems community will benefit from guidelines in those areas that have been well researched. While it may be practical to produce such guidelines, it is currently infeasible to aim for comprehensive standards. REFERENCES Abernethy, C.N. (1988). Human-computer interface standards: Origins, organizations and comment. International Reviews of Ergonomics, 2, 31-54. Berry, D.C., & Hart, A.E. (1990). Expert systems: Human issues. London: Chapman and Hall. Berry, D.C., & Broadbent, D.E. (1987). The user interface. Expert
Systems: The International Journal of Knowledge Engineering, 4, 18-27. Bice, K., & Lewis, C. (Eds.). (1989). Human factors in computing systems: Proceedings of CHl 89. New York: ACM Press. Billingsley, P. (1989). The standards factor. SIGCHI Bulletin, 21, 13-16. Grudin, J. (1989). The case against user interface consistency. Communications of the ACM, 32, 1165-1173. Helander, M.G., Billingsley, P.A., & Schurick, J.M. (1982). A critical review of human factors research of visual display terminals (Report No. CRG-TR-82-004). Morristown, NJ: Bell Labs. Hirsch, R.S. (1984). VDTs and the human factors community. Tipping the iceberg. Human Factors Society Bulletin, 27, 1-3. Holdaway, K., & Bevan, N. (1989). User system interaction Standards. Computer Communications, 12, 97-102. Kellogg, W.A. (1987). Conceptual consistency in the user interface. Effects on user performance. In H. J. Bullinger, B. Shackel, & K. Kornwachs (Eds.), Proceedings of INTERACT '87 Conference on Human-Computer Interaction (pp. 389-395). Amsterdam: North Holland. Kidd, A., & Cooper, M.B. (1985). Man-machine interface issues in the construction and use of an expert system. International Journal of Man-Machine Studies, 22, 91-102. Landauer, T.K. (1987). Relations between cognitived psychology and computer system design. In J.M. Carroll (Ed.), Interfacing thought. Cambridge, MA: MIT Press. McDonald, J.E., & Schvaneveldt, R.W. (1988). The application of user knowledge to interface design. In R. Guindon (Ed.), Cognitive
science and its applications for human-computer interaction. Hillsdale, N J: Lawrence Erlbaum. Marshall, C., Nelson, C., & Gardiner, M. (1987). Design guidelines. In M. Gardiner & B. Christie (Eds.), Applying cognitive psychology to user interface design. Chichester, U.K.: Wiley. Poison, P. (1988). The consequences of consistent and inconsistent user interfaces. In R. Guindon (Ed.), Cognitive science and its applications for human-computer interaction. Hillsdale, N J: Lawrence Erlbaum. Rogers, J.G., & Pegden, C.D. (1977). Formatting and organization of a human engineering standard. Human Factors, 19, 55-66. Rubinstein, R., & Hersh, H. (1984). The human factor. Bedford, MA: Digital Press. Shneiderman, B. (1987). Designing the user interface. Reading, MA: Addison-Wesley. Smith, S.L. (1986). Standards versus guidelines for designing user interface software. Behaviour and Information Technology, 5, 4761. Smith, S.L., & Mosier, J.N. (1986). GuidelinesJor designing user interface software (Report 7 MTR-10090, Esd-Tr-86-278). Bedford, MA: MITRE Corporation. Taylor, J.M. (1985). An expert system for terminal fault diagnosis.
Proceedings of the First International Expert Systems Conference on Learned Information. Oxford.