UML14 — Design patterns and collaboration templates.

The current UML definition of design pattern is oversimplifying the situation. The relationship between a design pattern and collaboration template is 1 to n. For any given design pattern, you can find any number of templates as formal abstract specifications of specific collaboration specifications.

The structure diagram in the GOF book illustrates one common abstract form of the design pattern, but certainly not the only one. Other variants, typically more complex ones, are hidden in the implementation section. The reason for this: in the opinion of its fathers, design patterns can not be formalized.

The best way to escape the debate of whether to formalize or not is to distinguish between a non-formalizable pattern and formalizable templates. This is also how people do it in practice, if you take a look at the many different abstract descriptions (= templates) of, say, the Observer pattern.

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