Methodology I: Task Analysis - Foundations for Designing User-Centered Systems - page 303

development when TA will be used, and then ask four interrelated questions for
each of the identified stages:
1. What knowledge do you want the TA to provide? Frequently this is not an easy
question to answer and your answer may need to be refined as you start to learn
more and uncover interesting issues.
2. What format should the output of the TA take? The output from a TA may not
map directly onto software engineering representations, so the contribution of a
TA may sometimes be indirect, e.g., building models of the world through TA
can improve the models that are used in software engineering.
3. What data can be collected? Data can be collected using several methods such
as observing performance, interviews, document analysis, training program
analysis, and analysis of existing systems.
4. Which method should be used? The choice should be based on knowledge
about the input data and the desired output data, rather than familiarity with a
particular method.
The results of a TA can be prescriptive or descriptive, depending on the aims of
the analyst. Prescriptive analyses show how the user should carry out the task, and
hence are associated with normative behavior. Prescriptive analyses can be used to
help create safety procedures, and standard operating procedures, which prescribe
how the user should carry out particular tasks. In contrast, descriptive analyses
show how users really carry out the task, and are hence associated with actual
behavior. Descriptive analyses are usually more situation specific than prescriptive
analyses. It is important to be able to distinguish between the two, however. A
prescriptive analysis of car driving, for example, would not include anything about
driving above the speed limit; a descriptive analysis would be more likely to
include details about people driving faster than the speed limit (perhaps only for
particular sections of the road network).
When thinking about the different types of TA that are available, it is important
to remember that there may be some slight differences in the way they use terms
such as goals, tasks, and actions. In general, goals are achieved by carrying out
tasks. These tasks are usually performed as a series of actions on some object.
In the rest of the chapter we first provide some examples of how task analysis
can be used before describing four approaches to TA. The different approaches
should be seen as complementary, as each has its own particular strengths and
weaknesses. Although the approaches are similar in several respects, such as the
need to apply them systematically, they also differ in many respects, such as the
types of development activities they can support, and the level of detail that they
can provide. For each of the different TA approaches we provide examples of how
they can be used, and note some of their strengths and weaknesses. We finish by
noting some of the limitations of TA.