 |
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
innovation¾in
this case the use of the Internet¾and
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.
|
|
Figure 1. Change cases.
|
Change case:
Registration will occur completely via the Internet.
Likelihood: Medium
likelihood within two to three years, very likely
within ten years.
Impact: Unknown.
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.
This artifact description is excerpted from Chapter 10
of
The Object Primer 3rd Edition: Agile Model Driven
Development with UML 2.
 |
|
This is the classic text on change cases, and frankly
it's a pretty good read for anyone interested in system
architecture. |
 |
|
The Object Primer 3rd Edition: Agile Model Driven
Development with UML 2 is an
important reference book for agile modelers,
describing how to develop 35
types of agile
models including all 13
UML 2 diagrams.
Furthermore, this book describes the techniques
of the
Full Lifecycle Object Oriented Testing
(FLOOT) methodology to give you the fundamental
testing skills which you require to succeed at
agile software development. The book also
shows how to move from your agile models to
source code (Java examples are provided) as well
as how to succeed at implementation techniques
such as
refactoring and
test-driven development
(TDD). The Object Primer also includes a
chapter overviewing the critical database
development techniques (database refactoring,
object/relational mapping,
legacy analysis, and
database access coding) from my award-winning
Agile Database Techniques
book. |
 |
|
Agile Modeling: Effective Practices for Extreme
Programming and the Unified Process is the seminal
book describing how agile software developers approach
modeling and
documentation. It describes principles and
practices which you can tailor into your existing
software process, such as
XP, the
Rational Unified Process (RUP), or the
Agile Unified Process (AUP), to streamline your
modeling and documentation efforts. Modeling and
documentation are important aspects of any software
project, including agile projects, and this book
describes in detail how to
elicit requirements,
architect, and then
design your system in an agile manner. |
 |
|
The Elements of UML 2.0 Style describes a collection
of standards, conventions, and
guidelines
for creating effective
UML diagrams. They are based on sound, proven
software engineering principles that lead to diagrams
that are easier to understand and work with. These
conventions exist as a collection of simple, concise
guidelines that if applied consistently, represent an
important first step in increasing your productivity as
a modeler. This book is oriented towards
intermediate to advanced UML modelers, although there
are numerous examples throughout the book it would not
be a good way to learn the UML (instead, consider
The Object Primer). The book is a brief 188
pages long and is conveniently pocket-sized so it's easy
to carry around. |
Translations
We actively work with clients around the world to
improve their information technology (IT) practices,
typically in the role of mentor/coach, team lead, or trainer. A full
description of what we do, and how to contact us, can be
found at Scott W.
Ambler + Associates.
 
|
