Deconstructing Reo

Abstract

Coordination in Reo emerges from the composition of the behavioural constraints of the primitives, such as channels, in a component connector. Understanding and implementing Reo, 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 Reo as a constraint satisfaction problem. Not only does this provide a clear intensional 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 propagation and satisfaction. In fact, decomposing Reo 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 Reo. de•con•struct verb [trans.]analyze (a text or linguistic or conceptual system) by deconstruction, typically in order to expose its hidden assumptions and contradictions and subvert its significance or unity.

Offer semantics: Achieving compositionality, flattening and full expressiveness for the glue operators in BIP

“…A formula in B[P , Ṗ ] defines the constraints on the firing of ports, based on their activation: in a given global state of the system, the valuations of the activation variables are determined by the enabled transitions of the components; a valuation of the firing variables that complements the valuation of the activation ones in such a manner, that the overall valuation satisfies the formula, defines an admissible interaction (for formal presentation, see [14]). Obviously, a port cannot participate in an interaction if it is not active, justifying axiom (26).…”

“…The comprehensive presentation of the key properties, required from a component-based framework for the design of concurrent software and systems, could be of relevance to other hierarchical frameworks, such as, for instance, Sofa [22], Koala [23] or rCos [24], and for languages implementing the Fractal specification [25]. The approach we used in [13] for the Boolean encoding of connectors is close to that used for computing flows in Reo connectors in [26], where it is further extended to data flow. In [27], the authors discuss the extension of the colouring semantics of Reo [28] from the 2-colouring to the 3-colouring model.…”

“…The only difference is that, in CR(P ∪Ṗ ∪ P ) we introduce the following additional axiom: ṗ ⇒ p, for all p ∈ P (cf. the discussion leading up to (26)). The first consequence of this extension is that, rather than extending the existing graphical representation of connectors, it can be used as is to express priorities and activation conditions (the use of the offer predicate in the positive premises of the rule (30)) by adding a trivalued attribute to ports: firing, activation and negative.…”

Extended Connectors: Structuring Glue Operators in BIP

“…Axiom 1(c) is a consequence of Lemma 4.7. In the Axiom 1(d), both pairs p and p, andṗ and p produce conflicting premises in the rule (13) and, therefore, do not generate any transitions. For the Axiom 5, we have…”

Program Components & Abstract Behavioral Types

“…Connector's simplest types are channels (Fig.:2). Channels as a set of simplest glue code was firstly defined in REO by Dr. Fahrad Arbab [1], [2], [3], [8], [9]. There is no requirement in channels to have defined a source and a sink end.…”