Specifying Structural Properties and Their Constraints Formally, Visually and Modularly Using VCL

Abstract

Abstract. The value of visual representations in software engineering is widely recognised. This paper addresses the problem of formality and rigour in visual-based descriptions of software systems. It proposes a new language, VCL, designed to be visual, formal and modular, targeting abstract specification at level of requirements, and that aims at expressing visually what is not visually expressible using mainstream visual languages, such as UML. This paper presents and illustrates VCL's approach to structural modelling based on the VCL notations of structural and constraint diagrams with a case study. VCL's contributions lie in its modularity mechanisms, and the support for two alternative styles of visual constraint modelling (one closer to set theory expressions and based on Euler diagrams, the other closer to predicate calculus and based on object graphs).

Modular Design by Contract Visually and Formally Using VCL

“…It introduces the notations of behavioural and contract diagrams. Work presented here, together with VCL's approach to structural modelling presented in [6], and VCL's coarse-grained modularity approach based on packages presented in [4] makes design of overall VCL, a language designed for modular abstract specification of software systems at level of requirements.…”

“…Usability. As discussed in [6], VCL has been designed to be well matched to meaning and to enable users to infer meaning from patterns, following usability guidelines. This can be observed in declarations, pre-conditions and post-condition compartments of contract diagrams, which closely mimic underlying structure of operations.…”

“…The 1.8% that could not be expressed visually corresponds to invariant TotalBalIsPositive (see Fig. 1) that could not be expressed visually and was expressed directly in Z by embedding the Z text into a CntD (see [6], [4]). …”

“…These claims are to be subject to empirical rigorous validation (future work). Currently, we are developing tool support for VCL 3 [6] to further enhance VCL's practical value.…”

“…This is why UML is accompanied by the textual Object Constraint Language (OCL). To address these problems, this paper proposes the Visual Contract Language (VCL) [4], [5], [6], a visual language for abstract specification of software systems at level of requirements (or high-level designs). It presents the design of VCL, outlining syntax and semantics of VCL notations of structural, behavioural, constraint, and contract diagrams, together with VCL's approach to behavioural modelling based on design by contract [7].…”