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I 186 Chapter 6 The process of interaction design

I 6.4.1 A simple lifecycle model for interaction design

We see the activities of interaction design as being related as shown in Figure 6.7.
This model incorporates iteration and encourages a user focus. While the outputs
from each activity are not specified in the model, you will see in Chapter 7 that our
description of establishing requirements includes the need to identify specific us-
ability criteria.
The model is not intended to be prescriptive; that is, we are not suggesting
that this is how all interactive products are or should be developed. It is based on
our observations of interaction design and on information we have gleaned in the
research for this book. It has its roots in the software engineering and HCI Iifecy-
cle models described below, and it represents what we believe is practiced in the
field.
Most projects start with identifying needs and requirements. The project may
have arisen because of some evaluation that has been done, but the lifecycle of the
new (or modified) product can be thought of as starting at this point. From this ac-
tivity, some alternative designs are generated in an attempt to meet the needs and
requirements that have been identified. Then interactive versions of the designs
are developed and evaluated. Based on the feedback from the evaluations, the
team may need to return to identifying needs or refining requirements, or it may
go straight into redesigning. It may be that more than one alternative design fol-
lows this iterative cycle in parallel with others, or it may be that one alternative at
a time is considered. Implicit in this cycle is that the final product will emerge in an
evolutionary fashion from a rough initial idea through to the finished product. Ex-
actly how this evolution happens may vary from project to project, and we return
to this issue in Chapter 8. The only factor limiting the number of times through
the cycle is the resources available, but whatever the number is, development ends
with an evaluation activity that ensures the final product meets the prescribed us-
ability criteria.

Final product
Figure 6.7 A simple interaction design model.