Actors and their Composition

Abstract.

Modern environments for modelling and designing concurrent computational systems increasingly support heterogeneous system models, which are characterised by different coordination mechanisms governing the interaction between concurrent components in different parts or at different levels of the model. These interaction semantics, also called models of computation, pose a major challenge to the definition of the meaning of heterogeneous models, especially if such a definition is to be independent of any specific set of models of computation, ways of describing actors, or notations for describing models. This paper makes three main contributions. (1) It presents a framework for describing the semantics of actors and models of computation. Its central notion is the concept of a model of computation as a program transformation that composes actor descriptions into a description of a composite actor. This framework is entirely independent of any specific syntax for describing actors, or any particular modelling language. (2) It uses this framework to describe properties of actor compositions and models of computation, and to classify and analyse them. (3) Finally, it discusses the implications of this theory for the design of languages for describing actors and models of computation.