Change cases (Bennett
1997) are used to describe new potential
requirements for a system or modifications to existing
requirements. Change cases are modeled in a simple
manner. You describe the potential change to your
existing requirements, indicate the likeliness of that
change occurring, and indicate the potential impact of
that change. Figure 1 presents two change cases, one
potential change that is motivated by technical
this case the use of the Internet-and
a second by a change in your business environment.
Notice how both change cases are short and to the point,
making them easy-to-understand. The name of a change
case should describe the potential change itself.
Registration will occur completely via the Internet.
likelihood within two to three years, very likely
within ten years.
Although registration will be available online
starting in September, we currently expect less than
one quarter of registrations to be made via the
Internet this year. Response time will be an issue
during the peak use periods, which are the two weeks
prior to the beginning of classes each term, as well
as the first week of classes.
Change case: The
university will open a new campus.
Likelihood: Certain. It
has been announced that a new campus will be opened
in two years across town.
Impact: Large. Students
will be able to register in classes at either
campus. Some instructors will teach at both
campuses. Some departments, such as Computer Science
and Philosophy, are slated to move their entire
programs to the new campus. The likelihood is great
that most students will want to schedule courses at
only one of the two campuses, so we will need to
make this easy to support.
Change cases can be identified throughout the course
of your overall development efforts, although I have a
tendency to create them when I'm focusing on
architectural modeling. Change cases are often the
result of brainstorming with your project stakeholders.
Good questions to consider include:
How can the business change?
What is the long-term vision for our organization?
What technology can change?
What legislation can change?
What is your competition doing?
What systems will we need to interact with?
Who else might use the system and how?
My experience is that you can use
change cases in a very agile manner. First, they enable
you to consider long term issues and potential changes
that your system may need to support. This puts you in
a position to make better architectural decisions, such
as choosing one platform over another, and thus increase
the chance that you're taking the best approach. This
in turn reduces your desire to overbuild your system
because you're not as worried about the architectural
choices you've made. Second, change cases provide an
easy way for you to justify architectural decisions that
you've made because you can show that you've considered
a wide range of issues. This can help to reduce the
politics that your team has to endure, allowing you to
spend more time actually building software instead of
attending meetings. Third, if you identify a very
high-likelihood change case you can simply write it up
as a normal requirement(s) with your stakeholders. They
can prioritize the requirement(s) as usual and your team
can then implement it as appropriate. Your architecture
should be based on real requirements, otherwise you risk
goldplating your system with "really cool" features that
your stakeholders don't actually need. Fourth,
they're simple. See the
Change Case Template available for free download.