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An interaction design project may aim to replace
or update an established system, or it may aim to develop
a totally innovative product with no obvious precedent. There
may be an initial set of requirements, or the project may
have to begin by producing a set of requirements from scratch.
Whatever the initial situation and whatever the aim of the
project, the users' needs, requirements, aspirations, and
expectations have to be discussed, refined, clarified, and
probably rescoped. This requires an understanding of,
among other things, the users and their capabilities, their
current tasks and goals, the conditions under which the product
will be used, and constraints on the product's performance.
As we discussed in Chapter 6, identifying
users' needs is not as straightforward as it sounds. Establishing
requirements is also not simply writing a wish list of features.
Given the iterative nature of interaction design, isolating
requirements activities from design activities and from evaluation
activities is a little artificial, since in practice they
are all intertwined: some design will take place while requirements
are being established, and the design will evolve through
a series of evaluationredesign cycles. However,
each of these activities can be distinguished by its own emphasis
and its own techniques.
This chapter provides a more detailed overview
of identifying needs and establishing requirements. We introduce
different kinds of requirements and explain some useful techniques.
The main aims of this chapter are to:
- Describe different kinds of requirements.
- Enable you to identify examples of
different kinds of requirements from a simple description.
- Explain how different datagathering
techniques may be used, and enable you to choose among them
for a simple description.
- Enable you to develop a "scenario,''
a "use case,'' and an "essential use case'' from
a simple description.
- Enable you to perform hierarchical
task analysis on a simple description.