June 2010 Edition
Computer Science Department, University of Cape Town
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Although unintuitive the actions for case 1 are consistent. In case 2, there is an inconsistency as an insert operation is present under 'delete' and 'create'. In case 3 a number of characteristics are inherited from case 1, however, access to insert functionality is not consistent. Although no option is ideal, on balance, case 1 would be preferred, case 2 is the least desirable.
A consistent interface is one where similar interactive situations are presented in a similar fashion and exhibits similar behaviours.
Consistency provides a firm foundation for a dialogue to proceed - if a designer ignores the principle of consistency, the user's ability to learn the system and operate effectively will be reduced dramatically.
You should read up more on this topic, but the following table may serve as a starting point.
| Common terminology | Standard measures of usability or performance mean that designers and user know that they are discussing the same concept. |
| Maintainability and evolveability | Standard implementation techniques facilitate program maintenance, because all programs can be expected to have a shared style and structure. |
| Common identity | House or industry standards for display style or screen layout ensure that all systems have the same "look and feel and are easily recognisable. |
| Less training | Knowledge can be transferred more easily from one system to another if standard command keys and other interaction techniques are adopted by interactive system designers. |
| Health and safety | Users are less likely to be surprised by unexpected system behaviour if standard controls and warnings are used. Unfriendly systems can be a source of stress. |
Five of these can be classified as design principles: 3, 4, 6, 7 and 9. The rest 1, 2, 5 and 8 can be considered design rules.
Three main elements of style which need to be considered when developing a corporate style guide are:
Which style is to be used?
How should colour, graphics and other overlays be applied?
Which interface components should be used and for which purpose , e.g. when should a button be used, when should a check box be used and so on?
Two learnability design principles, familiarity and predictability are contravened. One would not immediately associate the shut down operation with the start button and without prior knowledge one would not have any indication how to shut down the system. However, this is a minor criticism as once the route to the shut down option is learned it is easily accessed again in the future.
People have different ways of working A system preemptive approach may enforce a way of working that is not natural for all users. However, a system preemptive approach may be necessary to control certain processes such as a logon procedure before allowing access to an application. It would not be sensible to allow access to a system before verifying logon details. A system-guided approach may also preferred when a task is performed for the first time or for rarely performed tasks
New and novice users of an application are likely to initially need support when using a system. As they become more proficient they may develop specialised requirements or find certain features more useful, initial configuration cumbersome.
A customisable interface can be adapted to cater for on going and changing requirements. The danger of customisability is that a system may not be configured adequately for a particular user or a user could be presented with several configurations at different points in time, which may be confusing.
First reason is to ensure consistency across all product lines within the organisation and the second reason might be to speed up the design process; if fewer design choices are open to designers, it should take less time to produce a good design.
These guidelines are high level principles because they require further interpretation before being applied. (You may wish to refer to Activity 3).
Mistakes (some of which may be safety-critical), cognitive overload and, stress.
Guidelines may be based on psychological theory, however many are formulated from experience.
If there is no observable effect when an action is performed it will not be apparent that anything has happened. If an action cannot be performed a clear explanation as to why should be provided and the status of a long running task should also be displayed.
Not withstanding the advances in Artificial Intelligence, computer systems do not always handle situations sensibly. It is thus advisable to offer an option to allow system made changes to be reviewed and deemed appropriate, undone.