148 n Interface metaphors and conceptual models(as a container for discarded objects). One of these is to represent the place wheredisk icons are put in order to eject the corresponding disk from the disk drive. Thisimplies that one has to ‘throw away’ a disk in order to retrieve it. Do you think thatthese contradictions can cause conceptual problems, and if so can you suggestanother way of representing this operation at the interface?A counter-argument against conceptual confusion is to treat such problems as actuallearning experiences.For example, Carroll et al. (1988a) describe how theyobserved a user trying to tear off a sheet of paper from a stationery pad icon bydragging the cursor across an icon representing the stationery pad. The interface hadnot been designed to allow this action; sheets of paper could only be selected from amenu option. However, what Carroll et al. noted was that the invalid action enabledthe user to understand better the difference between menu-based and mouse-basedoperations. Accordingly, she developed a more elaborate mental model of theinterface.Paradoxically, it could be the case that the more unexpected and the morebizarre the interface metaphor is, the more likely the user will develop a betterunderstanding of the system. By carrying out inappropriate actions the user isenlightened as to what are the appropriate and permissable operations. Provided theuser is able to experience the ‘ah-ha’ phenomenon relatively easily, and not behumiliated or frustrated in the process, such a strategy may be very effective.However, where the interface metaphor contravenes deep-rooted expectations (cf.the voice mail system and the central heating control models discussed in Chapter 6)users may find it difficult to switch their models and adapt to the new way ofunderstanding how an object works. Furthermore, if the interface metaphor elicitsinappropriate actions that have undesirable consequences, such as unexpectedlydeleting files, the users may be reluctant to experiment further with the interface andhence never learn the full functionality of the system.The dividing line between what consititutes a good or a poor interface metaphoris by no means clear cut. But by being aware of users’ expectations about differentobjects’ behaviour in conjunction with having a thorough understanding of thesystem’s functionality and what aspects users are unlikely to understand about theUbiquitous computingn 149system, designers can begin to have a better understanding of what metaphors aremost appropriate (Erikson, 1990).. . . . . .. . . . .. . . . . . . . . . ..v... . . . ..z.:.:.:.x.:.*: . . . . . . . . . . . . . . . . . . . . . . ,... . . . . . . . .;;:::f 7.3 f Classification of interface metaphors for applications::i. . ._.:::.:: .~..:.~.:.:.~..:.:.:.:.x.:.:.: . . . . . . . . .The desktop metaphor and its composites have been the most successful andpervasive of all interface metaphors. There are other metaphors, however, whichhave been developed for applications other than information systems (see Chapter22). Table 7.1 presents some examples with their associated applications.An important consideration when searching for interface metaphors is theappropriate effect. This is the subjective and emotional impact that differentgraphical representations can convey (Verplank, 1988). The kinds of metaphors likespreadsheets and multi-agents may be very appealing to adults working in officeenvironments, but may be inappropriate for schoolchildren. Imaginary characterslike demons and wizards might be far more attractive. Some sketching techniques forhelping you to explore different metaphors by brainstorming are discussed inChapter 22.Table 7.1 Examples of applications and associated metaphors.Application area Metaphor Familiar knowledgeOperating environmentSpreadsheetsObject-oriented environmentsHypertextLearning environmentsFile storageMultimedia environmentsComputer supportedcooperative workThe desktopLedger sheetPhysical worldNotecardsTravelPilesRooms (each associated with adifferent medium/task)Multi-agentsOffice tasks, file managementColumnar tablesReal-world behaviourFlexible organization ofstructured textTours, guides, navigationCategorizing objects in terms ofurgency, projects and so onSpatial structure of buildingsTravel agents, butlers and otherserving roles::::.:.:.:.:<.:.y,:.:.:.:.:.: . . . . . . . . . . . . . . .. . . . . . . . .,...,.,.. . . . . .. . . ....:z_fg3: .7.4 1 Ubiquitous computing.I.!.y...y<>>; . . . . ,r.:.~,.~..:!:~.:.:.~..~.~~:.~ . . . . . . . . .Ubiquitous computing is a term coined by Weiser (1991) for ‘invisibly enhancingthe world that already exists’ (p. 61). The ultimate aim of ubiquitous computing is tomake the interface metaphor invisible to the user in the same way as computerConceptual models n 151Instead of you having to decide that you need to buy some more milk, or that theheating needs turning up or the trash needs emptying, a ‘society of objects’ in theform of virtual butlers, secretaries and housekeepers will organize and manageeverything for you! However, a problem with such extensive anthropomorphism isthat users may assume that the system is more intelligent than it is. When the virtualagents fail to behave as expected users may get frustrated. There is also the dangerthat designers could mislead users in undesirable ways.Question 7.4What is ubiquitous computing?Conceptual modelsConceptual models is the generic term that describes the various ways in whichsystems are understood by different people. Primarily these consist of (i) the wayusers conceptualize and understand the system and (ii) the way designersconceptualize and view the system.As we said in Chapter 6, whether interacting with devices, machines, computers,people or the physical world, people use their prior knowledge to develop mentalmodels to enable them to understand and predict their behaviour. A highlysuccessful approach in interface design is to capitalize on users’ existing knowledgeand the use of metaphors. However, the problem confronting designers who followthis approach is finding a suitable metaphor. The aim for designers is to help users todevelop accurate mental models of the system. As Donald Norman (1986, p. 46)puts it, ‘The problem is to design the system so that, first, it follows a consistent,coherent conceptualisation - a design model - and, second, so that the user candevelop a mental model of that system -a user model -