Conquering Fine-Grained Blends of Design Patterns

The reuse of design patterns in realistic software systems is often a result of blending multiple pattern elements together rather than instantiating them in an isolated manner. Pattern blends can manifest in heterogeneous ways, typically including overlaps and interlaces of inner class members taking part in the patterns implementation. The explicit description of pattern compositions is the key for (i) documenting the structure and the behavior of blended patterns and, (ii) more importantly, supporting the reuse of composite patterns across different software projects. In this context, this paper proposes a fine-grained composition language for describing varying blends of design patterns based on their structural and behavioural semantics. Pattern compositions are specified using an expressive, albeit simple, set of operators that allow for unifying, conjoining, concealing and externalizing pattern elements. The reusability and expressiveness of the proposed language are assessed through its application to 32 compositions of GoF patterns recurrently appearing in three different case studies: the OpenOrb middleware, and the JHotDraw and JUnit frameworks.