Visual Syntax of UML Class and Package Diagram Constructs as an Ontology

Diagrams are often studied as visual languages with an abstract and a concrete syntax (concrete syntax is often referred to as visual syntax), where the latter contains the visual representations of the concepts in the former. A formal specification of the concrete syntax is useful in diagram processing applications as well as in achieving unambiguous understanding of diagrams. Unified Modeling Language (UML) is a commonly used modeling language to represent software models using its diagrams. Class and package diagrams are two diagrams of UML. The motivation for this work is twofold; UML lacks a formal visual syntax specification and ontologies are under-explored for visual syntax specifications. The work in this paper, therefore, explores using ontologies for visual syntax specifications by specifying the visual syntax of a set of UML class and package diagram constructs as an ontology in the Web ontology language, OWL. The reasoning features of the ontology reasoners are then used to verify the visual syntax specification. Besides formally encoding the visual syntax of numerous UML constructs, the work also demonstrates the general value of using OWL for visual syntax specifications.