Abstract
Coordination in Reo emerges from the composition of the behavioural constraints of primitives, such as channels, in a component connector. Understanding and implementing Reo, however, has been challenging due to the interaction of the channel metaphor, which is an inherently local notion, and the non-local nature of the constraints imposed by composition. In this paper, the channel metaphor takes a back seat. We focus on the behavioural constraints imposed by the composition of primitives and phrase the semantics of Reo as a constraint satisfaction problem. Not only does this provide a clear description of the behaviour of Reo connectors in terms of synchronisation and data flow constraints, it also paves the way for new implementation techniques based on constraint satisfaction. We also demonstrate that this approach is more efficient than the existing techniques based on connector colouring.

Abstract

Abstract

Abstract
Orc and Reo are two complementary approaches to the problem of coordinating components or services. On one hand, Orc is highly asynchronous, naturally dynamic, and based on ephemeral connections to services. On the other hand, Reo is based on the interplay between synchronization and mutual exclusion, is more static, and establishes more continuous connections between components (services). The question of how Orc and Reo relate to each other naturally arises. In this paper, we present a detailed comparison between the two models. We demonstrate that embedding non-recursive Orc expressions into Reo connectors is straightforward, whereas recursive Orc expressions require an extension to the Reo model. For the other direction, we argue that embedding Reo into Orc would require significantly more effort. We conclude with some general observations and comparisons between the two approaches.

Abstract

Abstract
Coordination in R eo emerges from the composition of the behavioural constraints of the primitives, such as channels, in a component connector. Understanding and implementing R eo, however, has been challenging due to interaction of the channel metaphor, which is an inherently local notion, and the non-local nature of constraint propagation imposed by composition. In this paper, the channel metaphor takes a back seat, and we focus on the behavioural constraints imposed by the composition of primitives, and phrase the semantics of R eo as a constraint satisfaction problem. Not only does this provide a clear intensional description of the behaviour of R eo connectors in terms of synchronisation and data flow constraints, it also paves the way for new implementation techniques based on constraint propagation and satisfaction. In fact, decomposing R eo into constraints provides a new computational model for connectors, which we extend to model interaction with an unknown external world beyond what is currently possible in R eo.