7. design rules


7.2 It has been suggested in this chapter that consistency could be considered a major category of interactive principles, on the same level as learnability, flexibility and robustness. If this had been the case, which principles discussed in this chapter would appear in support of consistency?


The discussion of consistency suggested that it can take many forms, because it is usually referred to in relation to some other feature of the interaction between user and system. Mentioned already in the text we have consistency related to the following principles:

  • Familiarity - consistency with respect to prior real-world experience
  • Generalizability - consistency with respect to experience with the same system or set of applications on the same platform

In addition, we could interpret some other principles as contributors to consistency:

  • Affordance - consistency with understood intrinsic properties of an object, so a soft button on the screen should allow us to always 'push' on it to select some action
  • Predictability - consistency of system response with user's expectation, given the user has some information about past interaction history
  • Substitutivity - consistent permission from system to allow use of equivalent values for input and output
  • Commensurate effort - consistency of effort with respect to doing and undoing tasks
  • Response time stability - consistency of system response for similar actions

Some other principles for consistency from the text and elsewhere:

  • Consistency can be relative to the form of input/output expressions relative to the user's conceptual model of the system. An example in the text involves using keys whose relative positions are similar to commands for the systems (any set of four typewriter keys that form a diagonal to indicate up, down, left and right information for an input command).
  • As discussed in the exercise on colour, consistency can be with respect to social or cultural conventions (e.g., using red to indicate stop or hot, green for go, blue for cool).

Other exercises in this chapter

ex.7.1 (ans), ex.7.2 (ans), ex.7.3 (open), ex.7.4 (ans), ex.7.5 (ans), ex.7.6 (ans), ex.7.7 (tut), ex.7.8 (tut), ex.7.9 (open)

all exercises for this chapter