Executable Specifications with Data-flow Diagrams

Specifications of information systems applications are often based on the use of entity–relationship (ER) and data-flow diagrams (DFD), which cover, respectively, the conceptual modelling of data and funtions. This paper introduces VLP: an executable visual language for formal specifications and prototyping which integrates ER and DFD diagrams in a semantically rigorous and clear way. Unlike existing commercial products (so-called CASE tools), which can support goodquality documentation, simple forms of consistency checking and bookkeeping, VLP also supports executable specifications, which provide a prototype of the desired application. After reviewing the principles of VLP, the paper outlines the structure of the ECASET environment in which VLP is embedded. In particular, it shows how the environment supports the stepwise derivation of specifications, from informal to formal, and how it supports specification-in-the-large.