Design Patterns Explained

Chapter 21 • Design Patterns Reviewed 3O9
lem domain into the main set of responsibilities I always use (the
ConcreteComponent) and the variations I optionally have— my
decorators. Strategies decompose my problem into an object that
uses rules and the rules themselves.
Relationships Within a Pattern
I must admit, in my courses, I have some fun with a certain quote
from Alexander. After I have been talking about how great patterns
are for two-thirds of a day, I pick up Alexander's Timeless Way of
Building, turn to the end, and say
This book is 549 pages long. On page 545, which, I think
you will agree, is pretty close to the end, Alexander says,
"At this final stage, the patterns are no longer impor tant: ... " 1
I pause to say, "I wish he'd have told me this at the beginning and I
could have saved myself some time!" Then I continue to quote from
him: "The patterns have taught you to be receptive to what is real. " 2
I finish with, "If you read Alexander's book, you will know what is
real— the relationships and forces described by the patterns."
The patterns give us a way to talk about these. However, it is not
the patterns themselves that are important. This is true for software
patterns as well.
Patterns aren 't
really the important
thing
A pattern describes the forces, motivations, and relationships about Software patterns
a particular problem in a particular context and provides us with an are multidimen-
approach to addressing these issues. The Bridge pattern, for exam- sional descriptions
pie, is about the relationship between the derived classes of an
1. Alexander, C., Ishikawa, S., Silverstein, M., The Timeless Way of Building, New
York: Oxford University Press, 1979, p. 545.
2. ibid, p, 545.