Pattern Language - Aggregation in An Associative Network ("pattern Language")

Aggregation in An Associative Network ("pattern Language")

A pattern language, as thought by Alexander, contains links from one pattern to another, so when trying to apply one pattern in a project, a designer is pushed to other patterns that are considered helpful in its context.

In Alexander's book, such links are collected in the "references" part, and echoed in the linked pattern's "context" part - thus the overall structure is a directed graph. A pattern that is linked to in the "references" usually addresses a problem of lower scale, that is suggested as a part of the higher-scale problem. For instance, the "PUBLIC OUTDOOR ROOM" pattern has a reference to "STAIR SEATS".

Even without the pattern description, these links, along with meaningful names, carry a message: When building a place outside where people can spend time ("PUBLIC OUTDOOR ROOM"), consider to surround it by stairs where people can sit ("STAIR SEATS"). If you are planning an office ("WORKSHOPS AND OFFICES"), consider to arrange workspaces in small groups ("SMALL WORKING GROUPS"). Alexander argues that the connections in the network can be considered even more meaningful than the text of the patterns themselves.

The links in Alexander's book clearly result in a hierarchic network. Alexander draws a parallel to the hierarchy of a grammar - that is one argument for him to speak of a pattern language.

The idea of linking is generally accepted among pattern authors, though the semantic rationale behind the links may vary. Some authors, however, like Gamma et al. in Design Patterns, make only little use of pattern linking - possibly because it did not make that much sense for their collection of patterns. In such a case we would speak of a pattern catalogue rather than a pattern language.