Precise Notation for Design Patterns

LePUS is a formal, visual notation proposed for the specification of design patterns a-la GoF. It is described through the diagrams of several patterns. This article is the 1 of two, focusing on the fundamentals of LePUS. The upcoming 2 article will discuss relations between sets of entities and a PROLOG implementation. The Need for a Notation for Design Patterns Is it possible at all to give a formal specification to design patterns? Isn’t the lack of precision in their description inherent to their very nature? As suitable abstractions were not coined in English, patterns are approximated using several pages of lengthy narratives, accompanied by source code samples and incomplete diagrams depicting special cases. Yet the fuzziness of the specification of patterns is often viewed not as an unfortunate impediment but rather as a reflection of their fundamentally nebulous nature. It is inevitable, as this argument goes, that the specification language shall be imprecise, as a pattern is an abstraction that cannot be captured other than by inexact approximations and special cases. Beyond their unsound specification media, it is given that precise and coherent definitions are missing for even the most fundamental elements of design patterns, such as “inheritance” or even “class”, nonetheless language independent interpretations as needed for language independent creatures such as design patterns are intended. In the absence of a suitable specification language, the authors of the [GoF 95] catalog, like all other authors of the genre, resort to verbal narratives and case studies. Nevertheless, a careful investigation of this primary publication of design patterns reveals that much of the verbal descriptions has definite interpretations, at least in the context of a particular programming lani Available from http://www.math.tau.ac.il/~eden/bibliography.html#precise_notation_ for_design_patterns ii To be submitted to Journal of Object Oriented Programming. SIGS Publications. iii 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. iv Behind which stands a “quality without a name”, some add.