Design Patterns Explained

Thinking in Patterns
Chapter 12 • Solving the CAD/CAM Problem with Patterns 199
You have learned several patterns and have seen Alexander's phi- The steps to thinking
losophy of design: start with the big picture and add details. To in patterns
accomplish this on a software project, I use the following steps:
1. Find the patterns I have in my problem domain. This is the set
of patterns to be analyzed.
2. For the set of patterns to be analyzed, do the following:
a. Pick the pattern that provides the most context for the other
patterns.
b. Apply this pattern to my highest conceptual design.
c. Identify any additional patterns that might have come up.
Add them to the set of patterns to be analyzed.
d. Repeat for the sets of patterns that have not yet been
analyzed.
3. Add detail as needed to the design. Expand the method and class
definitions.
Admittedly this works only when you can understand the entire
problem domain in terms of patterns. Unfortunately, this does not
happen all the time. Design patterns give you the way to get
started and then you have to fill in the rest by identifying relationships
amongst the concepts in the problem domain. The method
for doing this uses commonality/variability ana lysis and is outside
the scope of this book. However, you can get more information
about CVA on this book's Web site at http://www.netobjectives.com/
dpexplained.
Thinking in Patterns: Step 1
In the previous chapters, I identified four patterns in the CAD/CAM 1. Identify the
problem. They are: patterns