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interactive systems. A detailed description of these factors follows; for each factor a
description of the associated criteria for their evaluation is also proposed.
The productivity and learnability factors
. The aim of the productivity factor is to
assess the level of effectiveness achieved in relation to the resources consumed by
the user and the system within a specific context of use. This factor is very similar to
the efficiency and effectiveness factors but the difference is that it focuses on the
number of useful outputs without considering unproductive actions.
2
The learnability factor, instead, studies the extent to which the features of an
interactive environment are easily understood and managed within a specific
context of use. Table
13.5
reports a list of usability factors and related criteria.
For example, the productivity criteria are: time behavior, resource utilization, and
loading time.
Several measures have been proposed to evaluate the criteria of each factor. For
example, for the time behavior criterion, the model proposes to calculate the time
spent on performing each productive task; for the loading time criterion it
Table 13.5 The relations among criteria and usability factors
Productivity Learnability Accessibility Universality Acceptability Usefulness
Accuracy
X
Appropriateness
X
Attractiveness
X
Consistency
X
X
X
Controllability
X
X
X
Dependability
X
Discretion
X
Familiarity
X
fault-Tolerance
X
Flexibility
X
X
X
Loading time
X
X
X
Minimal action
X
X
Minimal memory
load
X
X
X
X
Navigability
X
X
Nonobtrusiveness
X
Operability
X
X
Privacy
X
X
Readability
X
Resource utilization X
X
Safety
X
Security
X
Self-descriptiveness
X
X
X
Simplicity
X
X
X
Time behavior
X
Trustworthiness
X
Understandably
X
User guidance
X
X
X
2
Unproductive actions mean actions that do not directly or indirectly contribute to the task output
(i.e. help actions, search actions, undo actions).
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