Pattern Language

A pattern language, a term coined by architect Christopher Alexander, is a structured method of describing good design practices within a field of expertise. Advocates of this design approach claim that ordinary people can use it to successfully solve very large, complex design problems.

Like all languages, a pattern language has vocabulary, syntax, and grammar; but a pattern language is applied to some complex activity other than communication. In pattern languages used for design, the parts break down in this way:

• The language description, the vocabulary, is a collection of named, described solutions to problems in a field of interest. These are called "design patterns." So, for example, the language for architecture would describe items like: settlements, buildings, rooms, windows, latches, etc.
• Each solution includes "syntax," a description that shows where the solution fits in a larger, more comprehensive or more abstract design. This automatically links the solution into a web of other needed solutions. For example, rooms have ways to get light, and ways to get people in and out.
• The solution includes "grammar" that describes how the solution solves a problem or gets a benefit. So, if the benefit is not needed, the solution is not used. Perhaps that part of the design can be left empty to save money or other resources. So, if people do not need to wait to enter a room, instead of a waiting room, perhaps you can use a simple doorway.
• In the language description, the grammar and syntax cross index (often with a literal alphabetic index of pattern names) to other named solutions, so the designer can quickly think from one solution to related, needed solutions, and document them in a logical way. In Alexander's book, the patterns are in decreasing order by size, with a separate alphabetic index.
• The web of relationships in the index of the language allows for many different paths through the design process. This simplifies the designer's life, because the design process can start from any part of the problem that the designer understands, and work toward the unknown parts. At the same time, if the pattern language has worked well for many projects, there is reason to believe that even though the designer may not completely understand the design problems at first, the process will complete, and the resulting design will be usable. For example, skiers coming inside will need to shed snow and store equipment. The messy snow and boot cleaners should stay outside. The equipment needs care, so the racks should be inside. etc.
• It really is a language: There is even an analogy to spelling or phonology, in the documentation standards for the designs and patterns. Without these, the people building the design won't be able to read the design.