Precise visual specification of design patterns

Abstract

Abstract. There has been substantial recent interest in captured design expertise expressed as design patterns. Prevalent descriptions of these design patterns suffer from two demerits. Firstly, they capture specific instances of pattern deployment, rather than the essential pattern itself, thus the spirit of the pattern is often lost in the superfluous details of the specific instances described. Secondly, existing pattern descriptions rely upon relatively informal diagrammatic notations supplemented with natural language annotations. This can result in imprecision and ambiguity. This paper addresses these problems by separating the specification of patterns into three models (role, type, and class). The most abstract (role-centric) model presents patterns in their purest form, capturing their essential spirit without deleterious detail. A role-model is refined by a type-model (adding usuallydomain-specific constraints), which is further refined by a class-model (forming a concrete deployment). We utilise recent advances in visual modelling notation to achieve greater precision without resorting to obtuse mathematical symbols. A set-oriented view of state, operations, and instances is adopted, permitting their abstract presentation in models via this visual notation. This paper utilises these ideas in the unambiguous specification of a selection of prominent design patterns. The expectation is that precise visual pattern specification will firstly enable clear communication between domain experts and pattern writers (and ultimately pattern users), and secondly enable CASE tool support for design patterns, permitting the designer (pattern user) to operate at a higher level of abstraction without ambiguity.

Formal Foundation for Pattern-Based Modelling

“…A distinction between roles, types and classes is used in [8] to decouple representations of roles, at which level the semantics of the pattern is abstractly described by incorporating constraint diagrams into the UML notation, from their refinement as types, and their implementation into classes. This way, the GoF presentation of patterns is shown to be a realization of the abstract level.…”

UML Support for Designing Software Systems as a Composition of Design Patterns

“…al. [20] take a visual specification approach to design patterns. They utilize constraint diagrams that are developed by Kent [19] together with UML diagrams.…”

Formalizing spider diagrams

“…In fact, spider diagrams can be thought of as constraint diagrams without the arrows. Constraint diagrams proved to be an intuitive and useful tool for design, and several extensions of these were proposed, including a variant designed for expressing pre-and post-conditions pairs [9], a three dimensional version for behavioral specification [3], and a version used for metaspecification, i.e., the specification of design patterns [10]. At the same time, constraint diagrams were employed in the software industry to produce informal descriptions of systems.…”