EXERCISE 7.2
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?
answer
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).
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