Design Patterns Explained

Alexander's Steps Discussion
Identify patterns
Start with context
patterns
Then, work inward
from the context
Refine the design
Implement
Chapter 11 • How Do Experts Design? 193
Identify the patterns that are present in your
problem. Think about your problem in terms of
the patterns that are present. Remember, the
purpose of the pattern is to define relationships
among entities.
Identify the patterns that create the context for the
other patterns. These should be your starting
point.
Look at the remaining patterns and at any other
patterns that you might have uncovered. From
this set, pick the patterns that define the context
for the patterns that would remain. Repeat.
As you refine, always consider the context implied
by the patterns.
The implementation incorporates the details dictated
by the patterns.
Using Alexander in software design: a
personal observation.
The first time I used Alexander's approach, I took his words too
literally. His concepts— rooted in architecture— do not usua lly
translate directly to software design (or other kinds of design). In
some ways, I was lucky in my early experiences in using design
patterns in that the problems I solved had the patterns follow
pretty well-defined orders of context. However, this also worked
against me in that I naively assumed that this method would
work in general (it does not).