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6.2 What is interaction design about? 169

sign. During this time, prototypes may be built or perspectives may be drawn to
give clients a better indication of the design being developed. Detail design speci-
fies all components, and working drawings are produced. Finally, the job arrives on
site and building commences.
We will be expanding on each of the basic activities of interaction design in the
next two chapters. Here we give only a brief introduction to each.

Identifying needs and establishing requirements
In order to design something to support people, we must know who our target
users are and what kind of support an interactive product could usefully provide.
These needs form the basis of the product's requirements and underpin subsequent
design and development. This activity is fundamental to a user-centered approach,
and is very important in interaction design; it is discussed further in Chapter 7.

Developing alternative designs
This is the core activity of designing: actually suggesting ideas for meeting the re-
quirements. This activity can be broken up into two sub-activities: conceptual design
and physical design. Conceptual design involves producing the conceptual model for
the ~roduct, and a conceptual model describes what the product should do, behave
and look like. Physical design considers the detail of the product including the col-
ors, sounds, and images to use, menu design, and icon design. Alternatives are con-
sidered at every point. You met some of the ideas for conceptual design in Chapter
2; we go into more detail about conceptual and physical design in Chapter 8.

Building interactive versions of the designs
Interaction design involves designing interactive products. The most sensible way
for users to evaluate such designs, then, is to interact with them. This requires an
interactive version of the designs to be built, but that does not mean that a software
version is required. There are different techniques for achieving "interaction," not
all of which require a working piece of software. For example, paper-based proto-
types are very quick and cheap to build and are very effective for identifying prob-
lems in the early stages of design, and through role-playing users can get a real
sense of what it will be like to interact with the product. This aspect is also covered
in Chapter 8.

Evaluating designs
Evaluation is the process of determining the usability and acceptability of the prod-
uct or design that is measured in terms of a variety of criteria including the number of
errors users make using it, how appealing it is, how well it matches the requirements,
and so on. Interaction design requires a high level of user involvement throughout
development, and this enhances the chances of an acceptable product being deliv-
ered. In most design situations you will find a number of activities concerned with