Information Technology Reference
In-Depth Information
consumed 80 percent of the budget.”). Finally, how the project manager
would see variety in a project ultimately determines the management and
control mechanisms that will be put in place. Good managers choose
sufficient variety to control what needs controlling, as per Ashby's law.
However, this is easier said than done, as we will see.
Variety Is Relative
Although it may appear simple, in theory, to determine the variety in any
system, it is not so easy in practice. Various estimation approaches such as
COCOMO, FPA, and ESTIMACS have been proposed and are used selectively
by software managers. Ashby's law, in a way, simplifies the model because
the regulation of variety focuses on “relative” parameters of complexity
rather than “absolute” ones. For example, if you add new functionality to
your application, it must be met with increased variety on the Quality
Assurance (QA) side. QA acts as the control system for Engineering, deciding
whether or not the delivered code is acceptable for release. For example,
if your application must be enhanced to work with mobile phones, your
test plans must be enhanced to test that it works with mobile phones. If
you increase the variety in Development, then you have to increase corre-
sponding variety on the QA side. If such action to “destroy variety” is not
taken, then the QA system will fail to uncover some problems due to lack
of proper testing. This seems obvious to any development team that takes
it for granted that they would introduce new functionality with correspond-
ing changes to their testing plans. The reason we do that, or need to do
that, is explained by Ashby's Law of Requisite Variety.
Matching Variety
In information processing terms, the Law of Requisite Variety also implies
that a system's information processing capacity should match its informa-
tion processing requirements. If the information processing capacity is
less than the processing requirements, then crucial information may be
left unprocessed. Conversely, if an organization's information processing
capacity far exceeds its requirements, the organization has room to meet
new needs.
Any regulation can be attempted, or achieved, in two ways: (1) either
the variety of the environment can be reduced or (2) the variety of the
controller can be increased. Both approaches can be applied to software
design and development. Using the first approach, one can decrease
the external information processing requirements to match the available
