Design Patterns Explained

that it shared its patterns with other comparable things;
specific in the sense that it is unique, according to its circumstances.
The language is a sequence of these operators, in which
each one further differentiates the image, which is the
product of the previous differentiations. 6
Chapter 11 • How Do Experts Design? 191
Alexander asserts that design should start with a simple statement
of the problem, then make it more detailed (complex) by injecting
information into the statement. This information takes the form of a
pattern. To Alexander, a pattern defines relationships between the
entities in his problem domain.
For example, consider the Courtyard pattern discussed in Chapter 5,
"An Introduction to Design Patterns." The pattern must describe the
entities that are involved in a courtyard and how they relate. Entities
such as
• The open spaces of the courtyard
• The crossing paths
• The views outward
• And even the people who are going to use the courtyard
Thinking in terms of how these entities need to relate to each
other gives us a considerable amount of information with which to
design the courtyard. We refine the design of the courtyard by
thinking about the other patterns that would exist in the context of
the courtyard pattern, such as porches or verandas facing the
courtyard.
6. ibid, pp. 372-373.