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6.4 Lifecycle models: showing how the activities relate 195

0 UETask

T Development Task
() Decision Point
Documentation
+ Complex Applications
- -t Simple Applications
(e.g. websites)
I
Figure 6.14 (continued).

Mayhew herself says, "I did not invent the concept of a Usability Engineering Life-
cycle. Nor did I invent any of the Usability Engineering tasks included in the lifecy-
cle . . . .". However, what her lifecycle does provide is a holistic view of usability
engineering and a detailed description of how to perform usability tasks, and it
specifies how usability tasks can be integrated into traditional software develop-
ment lifecycles. It is therefore particularly helpful for those with little or no exper-
tise in usability to see how the tasks may be performed alongside more traditional
software engineering activities. For example, Mayhew has linked the stages with a
general development approach (rapid prototyping) and a specific method (object-
oriented software engineering (OOSE, Jacobson et al, 1992)) that have arisen from
software engineering.
The lifecycle itself has essentially three tasks: requirements analysis, design1
testingldevelopment, and installation, with the middle stage being the largest and
involving many subtasks (see Figure 6.14). Note the production of a set of usability
goals in the first task. Mayhew suggests that these goals be captured in a style guide
that is then used throughout the project to help ensure that the usability goals are
adhered to.
This lifecycle follows a similar thread to our interaction design model but in-
cludes considerably more detail. It includes stages of identifying requirements, de-
signing, evaluating, and building prototypes. It also explicitly includes the style
guide as a mechanism for capturing and disseminating the usability goals of the
project. Recognizing that some projects will not require the level of structure pre-
sented in the full lifecycle, Mayhew suggests that some substeps can be skipped if
they are unnecessarily complex for the system being developed.

Study the usability engineering lifecycle and identify how this model differs from our inter-
action design model described in Section 6.4.1, in terms of the iterations it supports.

Comment One of the main differences between Mayhew's model and ours is that in the former the it-
eration between design and evaluation is contained within the second phase. Iteration be-
tween the design/testldevelopment phase and the requirements analysis phase occurs only
after the conceptual model and the detailed designs have been developed, prototyped, and