Ajax Design Patterns

Appendix C. Patterns and Pattern Languages

ONE SIDE BENEFIT OF THIS PROJECT HAS BEEN TO SEE HOW “PATTERNS” ARE BEING ACCEPTED BY THE development community. Since the Ajax Patterns began to be published, the focus has always been on the “Ajax” and not the “Patterns.” For patterns, this is a good thing, and a welcome change from the late ’90s, when you not only had to explain the concept but also justify its existence. “Ajax” itself is a pattern—one whose popularity is further evidence for the power of “just a name.” For all these reasons, this discussion of patterns and their relationship to Ajax Patterns is kept brief.

Patterns came about in the late 1970s, after Christopher Alexander and colleagues spent years studying the towns and buildings of many diverse cultures. The findings were summarized as 253 distinct patterns, derived from a global pattern describing the division of nations to town-planning patterns such as “Market of Many Shops,” all the way down to building patterns like “Soft Tile and Brick.” Each pattern is a “thing” you often see in good designs, combined with instructions on making the thing.

Patterns have mostly been confined to academia in their original field, but they have really taken off in software design. Their rise over the past decade has been a great boon to the industry, allowing us to learn about design from real examples and not just vague comments about cohesion, coupling, and encapsulation. The pool of real examples to draw upon has itself risen ...