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Abstract:

The specification and development of a large, complex system might involve the construction of a variety of models, each of which might address a di#erent aspect of design. Where two or more models are proposed for the same component, it is useful to be able to compare them, and check that the views they present are consistent. If the models are constructed in the same language, this comparison is a question of refinement. If di#erent languages are employed, then some translation is required. This thesis investigates the problem of translation between two kinds of model: those in which systems are described in terms of states, and transformations upon them; and those in which systems are described in terms of the occurrence and availability of events. It shows how models constructed in the former, state-based approach can be translated into, and thus compared within, an event-based framework. The notation chosen for state-based models is that of Z; the event-based framework is derived from the theory of Communicating Sequential Processes (CSP). A theory of event-based refinement, using a new semantic model for CSP, is developed to match the theory of refinement for abstract data types written in Z: in this model, process refinement corresponds exactly to data refinement. The resulting theory of refinement can be used to show consistency and refinement of object-oriented specifications. The thesis shows how both state-based and event-based descriptions, written in the graphical language UML might be translated into either Z or CSP, and compared using the theory of data refinement. ii

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