Towards a formal foundation of the specification and description language SDL

A formal model is described for the CCITT specification and description language SDL which provides a graphical concept for representing designs of systems interacting by signals. The model is based on functional descriptions of interactive systems using the concept of streams and stream processing functions. The foundations for this functional modelling of interactive systems are introduced. The graphical constructs of SDL are related to this model. In particular it is shown how the meaning of SDL graphical forms can be represented by specifications in the form of conditional equations or by functional programs. Based on the functional formal model the application of specification and verification methods for SDL is demonstrated. Small examples are treated. A number of tools are discussed that can be based on that model. This study does not define a semantic model for the specification and design language SDL, but it gives An introduction to the functional modelling of distributed systems An explanation of how to translate SDL designs into functional descriptions An extended example for the translation of an SDL design A discussion of the possibilities of supporting SDL designs by such a semantic foundation