Software Design 2e - DIM

Table 4.1The cognitive dimensions73DimensionAbstractionHidden dependenciesPremature commitmentSecondary notationViscosityVisibilityCloseness of mappingConsistencyDiffusenessError-pronenessHard mental operationsProgressive evaluationProvisionalityRole-expressivenessInterpretationTypes and availability of abstraction mechanismsImportant links between entities are not visibleConstraints on the order of doing thingsExtra information provided via means other than formal syntaxResistance to changeAbility to view components easilyCloseness of representation to domainSimilar semantics are expressed in similar syntactic formsVerbosity of languageNotation invites mistakesHigh demand on cognitive resourcesWork-to-date can be checked at any timeDegree of commitment to actions or marksThe purpose of a component is readily inferredAssessing design qualityWhile the ideas concerned have been couched largely in the terminology of HCIand of the more visual aspects of systems, they have nevertheless something useful tooffer to the more general process of design. In this section, therefore, we briefly reviewsome of the more directly relevant dimensions and suggest where they may be able tooffer some particularly useful insight.Table 4.1 summarizes the cognitive dimensions and their meanings. (For a fullerdiscussion of the complete framework, readers should consult the above references andalso the website at http://www.cl.cam.ac.uk/~afb21/CognitiveDimensions/.)As concepts, many of these provide a rather different insight into the issue of howwe might think about and assess a design, although clearly not all are directly relevantto the current discussion. To explain how these might help with thinking about designquality and attributes, it may be useful to consider some small examples that illustratesome of the more relevant dimensions.Premature commitment (and enforced lookahead)This arises when an early design decision which was made before proper informationwas available has the effect of constraining later ones. It may be unavoidable (informationmay not be available within a practical timescale), but it may also arise throughthe use of procedural design practices such as design methods that encourage a particularordering in the decision-making process. (As a simple example, a spoken telephonemenu system, especially one using a hierarchy of menus, tends to encourage this characteristic.Each set of choices is presented in turn and the user must make a decisionwhile lacking a full knowledge of what other choices will be available later.)Although intended as a ‘measure’ that can be applied to HCI designs, for ourpurposes, this concept can provide a ‘measure’ of the quality of the design process,rather than of the design product, although obviously the consequences are likely to beexhibited in the latter. A life-cycle which allows design decisions to be revisited mayhelp, as will a design process which recognizes the need to make several iterationsthrough the decision-making steps.