Giving “The Quality” a Name Precise Specification of Design Patterns: A Second Look at the Manuscripts

We discuss the prospects of precise specification of design patterns. We analyze the manuscript of the GoF patterns catalog, and prove that the essence of many design patterns can be preserved through the translation to some formal language. Contemporary Means of Specification There is widespread interest in design patterns [GoF 95; Coplien & Schmidt 95; Vlissides, Coplien & Kerth 96; Buschmann et. al 96; Pree 94; Martin, Riehle & Buschmann 97], and in the “pattern” form as means of conveying expertise in software design. In particular, the universal applicability of the constructs listed in the GoF [95] catalog took over the industry’s attention and grew to serve as building blocks in the documentation, reasoning, and construction of object oriented software. Design patterns convey regularities, plans, aspects, or abstractions of programs rather than concrete instances. Therefore most design patterns have each an unbounded number of implementations, usually in various programming languages and numerous application domains. In lack of a dedicated specification language, design patterns are invariably communicated through a list of prototypical instances, source code of simplified implementations, and class (or object) diagrams thereof. As specific instances of design patterns cannot account for the generalizations intended, specification manuscripts consist mostly of natural language narrative. As a result, “clients” of design patterns are compelled to project from the given examples or to interpret the designation of the verbal description that should apply to their context of interest. To summarize, the prevalent means of their specification are not sufficiently rigorous to allow unambiguous interpretation. 1 http://www.math.tau.ac.il/~eden/bibliography.html#giving_the_quality_a_name 2 Guest column, June 1998, Journal of Object Oriented Programming. SIGS Publications. 3 Supported in part by a grant from the German-Israeli Foundation for Scientific Research and Development (GIF) and the Israel Ministry of Science and Arts. 4 Department of Computer Science, Schriber School of Mathematics, Tel Aviv University.