Specifying structural properties and their constraints formally, visually and modularly using VCL

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).