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166 Chapter 6 The process of interaction design

were introduced in Chapter 1. We also introduce a lifecycle model of interaction
design that captures these activities and characteristics.
The main aims of this chapter are to:
Consider what 'doing' interaction design involves.
Ask and provide answers for some important questions about the interaction
design process.
Introduce the idea of a lifecycle model to represent a set of activities and
how they are related.
Describe some lifecycle models from software engineering and HCI and dis-
cuss how they relate to the process of interaction design.
Present a lifecycle model of interaction design.

6.2 What is interaction design about?
There are many fields of design, for example graphic design, architectural design,
industrial and software design. Each discipline has its own interpretation of "de-
signing." We are not going to debate these different interpretations here, as we are
focussing on interaction design, but a general definition of "design" is informative
in beginning to understand what it's about. The definition of design from the Ox-
ford English Dictionary captures the essence of design very well: "(design is) a plan
or scheme conceived in the mind and intended for subsequent execution." The act
of designing therefore involves the development of such a plan or scheme. For the
plan or scheme to have a hope of ultimate execution, it has to be informed with
knowledge about its use and the target domain, together with practical constraints
such as materials, cost, and feasibility. For example, if we conceived of a plan for
building multi-level roads in order to overcome traffic congestion, before the plan
could be executed we would have to consider drivers' attitudes to using such a con-
struction, the viability of the structure, engineering constraints affecting its feasibil-
ity, and cost concerns.
In interaction design, we investigate the artifact's use and target domain by
taking a user-centered ap'proach to development. This means that users' concerns
direct the development rather than technical concerns.
Design is also about trade-offs, about balancing conflicting requirements. If we
take the roads plan again, there may be very strong environmental arguments for
stacking roads higher (less countryside would be destroyed), but these must be bal-
anced against engineering and financial limitations that make the proposition less
attractive. Getting the balance right requires experience, but it also requires the de-
velopment and evaluation of alternative solutions. Generating alternatives is a key
principle in most design disciplines, and one that should be encouraged in interac-
tion design. As Marc Rettig suggested: "To get a good idea, get lots of ideas" (Ret-
tig, 1994). However, this is not necessarily easy, and unlike many design disciplines,
interaction designers are not generally trained to generate alternative designs.
However, the ability to brainstorm and contribute alternative ideas can be learned,
and techniques from other design disciplines can be successfully used in interaction