Industry is looking to create a market in reliable “plug-and-play” components. To model components in a modular style it would be useful to combine event-based and state-based reasoning. One of the first steps in building an event-based model is to decide upon a set of atomic actions. This choice will depend on the formalism used, and may restrict in quite unexpected ways what we are able to formalise. In this paper we illustrate some limits to developing real world processes using existing formalisms, and we define a new notion of refinement, vertical refinement, which addresses some of these limitations. We show that using vertical refinement we can rewrite a specification into a different formalism, allowing us to move between handshake processes, broadcast processes and abstract data types.
