Composition of interacting computations

Abstract

The field of programming has been concerned with software composition since its very inception. Our models for software composition have brought us up to a new plateau of software complexity and composition. To tackle the challenges of composition at this level requires new models for software composition centered on interaction as a first-class concept. Interaction has been studied as an inseparable concern within concurrency theory. Curiously, however, interaction has not been seriously considered as a first-class concept in constructive models of computation. Composition of systems out of autonomous subsystems pivots on coordination concerns that center on interaction. Coordination models and languages represent a recent approach to design and development of concurrent systems. In this chapter, we present a brief overview of coordination models and languages, followed by a framework for their classification. We then focus on a specific coordination language, called Reo, and demonstrate how it provides a powerful and expressive model for flexible composition of behavior through interaction. Reo serves as a good example of a constructive model of computation that treats interaction as a (in fact, the only) first-class concept. It uniquely focuses on the compositional construction of connectors that enable and coordinate the interactions among the constituents in a concurrent system, without their knowledge. We show how Reo allows complex behavior in a system to emerge as a composition of primitive interactions. © 2006 Springer-Verlag Berlin Heidelberg.