Overview

Design in the object-oriented world has taken an odd turn in recent years. The usual course of design in the software world is revolution upon revolution. Every new generation of designer ignores what came before and builds a new way of doing what needs doing. The evolution of programming languages over the last 30 years reflects this revolutionary way of thinking, to the consternation of experienced language designers.

In the OO world, designers have begun to accept that there are aspects of design that should not change, or should change very little. Much of the rationale for this thinking comes from the fact that OO designers emphasize reusability. Once OO thinking moved beyond programming, designers realized that some of the lessons of architectural design thinking and philosophy could apply just as well to software design. These software architects adapted the work of Christopher Alexander, the great architectural philosopher, to software design through the concept of the pattern:

Design patterns capture solutions that have developed and evolved over time. Hence they aren't the designs people tend to generate initially. They reflect untold redesign and recoding as developers have struggled for greater reuse and flexibility in their software. Design patterns capture these solutions in a succinct and easily applied form. [Gamma et al. 1995, p. xi]

The essence of a pattern is tradition. The tradition is the core of the solution. The funny thing about traditions is that they constantly...