On the definition of visual languages and their editors

Different diagrammatic languages are concrete variants of a core metamodel which specifies the way in which to express relations, and which is the basis for a semantic interpretation. In this paper, we identify families of diagrammatic languages exploiting the notion of metamodel as introduced in UML, i.e. through an abstract syntax, given as a class diagram, and a set of constraints in a logical language. The abstract syntax constrains the types of expressable relations and the types and multiplicities of the participating entities. The constraints express contextual and global properties of the relations and their participants. We propose a set of metamodels describing common types of diagrammatic languages. The advantages of this proposal are manifold: the analysis of constraints in the metamodel can be used to assess the adequacy of a type of language to a domain semantics and it is possible to check whether a concrete notation or syntax complies with the metamodel or introduces unforeseen constraints. Finally, we discuss how this characterisation allows the definition of flexible editors for concrete diagrammatic languages, where a specific editor results from the specialisation of some high-level construction primitives for the relevant family of languages.