Integrating structured and formal methods: A visual approach to VDM

Two barriers to the widespread industrialisation of formal methods are a lack of methodology, and the use of mathematical notations that are not easily understood by the non-specialist. The work presented in this paper addresses these problems by defining diagrams which may be used to visualise aspects of formal specifications. The diagrams used are adaptations of classical approaches such as entity-relationship and state-transition diagrams. The approach described imposes a methodology on the early stages of system specification, and provides the analyst with a choice of notations, visual and non-visual, while maintaining an underlying formality. During the process of analysis, the notation most appropriate for the expression and communication of the concepts required can be selected. Two sorts of diagram are discussed: Entity-Structure Diagrams, and Operation-State Diagrams, the former in detail, the latter in sketch form. A tool is envisaged that assists the analyst in moving between diagrams and VDM. Each diagram can be mapped onto parts of a common VDM specification, which forms the central underlying system description. Consistency can then be checked by a VDM type-checker.