Software Components: a Formal Semantics Based on Coloured Petri Nets

Abstract

This paper proposes a component model compliant with the current practice of Software Engineering, yet provided with a sound formal semantics based on Coloured Petri nets. Our proposal is structured as follows: 1) Define a component model. We have chosen a component model inspired by the CORBA Component Model (CCM), yet simpler and more precise. 2) Propose a notation to formally specify the internal behaviour of a software component. Our formal approach is based on Coloured Petri nets which makes it well suited to the modelling of concurrent, distributed or event-driven systems, and amenable to formal verification. 3) Define a mapping from the constructs of the component model (facets, receptacles, event sources and sinks) to the constructs of the Petri-net based behavioural specification (e.g. places, transitions, etc.). 4) Provide a formal definition of inter-components communication primitives, (invocation of methods, event-based communication). This definition is also given in terms of Petri nets. 5) Provide a denotational semantics of an assembly of components, in order to define the behaviour of such a system in terms of the individual behaviour of each component and of the formal definition of inter-component communication primitives.The expected benefits of such an approach are threefold: 1) Offer a convenient notation for describing the internal behaviour of concurrent and distributed software components, 2) Provide a formal, unambiguous semantics of component features such as event multicast or service invocation, 3) And, with the previous two being necessary conditions, offer some means to reason about assemblies of components designed with this approach, in particular to mathematically verify properties on them.