Pattern language

A pattern language is a method of describing good design practices within a field of expertise. The term was coined by architect Christopher Alexander and popularized by his book A Pattern Language. A pattern language is an attempt to express the deeper wisdom of what brings aliveness within a particular field of human endeavor, through a set of interconnected expressions arising from that wisdom. Aliveness is one placeholder term for ""the quality that has no name"": a sense of wholeness, spirit, or grace, that while of varying form, is precise and empirically verifiable. Some 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 applies to some complex activity other than communication. In pattern languages 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 describes 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 produces a benefit. So, if the benefit is unneeded, the solution is not used. Perhaps that part of the design can be left empty to save money or other resources; if people do not need to wait to enter a room, a simple doorway can replace a waiting room. In the language description, 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 provides many paths through the design process.This simplifies the design work because designers can start the process from any part of the problem they understand 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 a designer who does not completely understand the design problem at first will complete the design process, and the result will be usable. For example, skiers coming inside must shed snow and store equipment. The messy snow and boot cleaners should stay outside. The equipment needs care, so the racks should be inside. 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.