Automata for Analysing Service Contracts

Abstract

Abstract. A novel approach to the formal description of service contracts is presented in terms of automata. We focus on the basic property of guaranteeing that in the multi-party composition of principals each individual gets his requests satisfied, so that the overall composition reaches its goal. Depending on whether requests are satisfied synchronously or asynchronously, we construct an orchestrator that at static time either yields composed services enjoying the required properties or detects the individuals responsible for possible violations. To do that in the asynchronous case we resort to techniques from Operational Research.

Relating two automata-based models of orchestration and choreography

“…In a choreographed model, the distributed components autonomously execute and interact with each other on the basis of a local control flow expected to comply with their role as specified in the "global viewpoint". Here we investigate the relations between two models of distributed coordination: contract automata [3] and communicating machines [4].…”

“…For this purpose, we first introduce the notion of strong agreement on contract automata, that requires the fulfilment of all offers and requests, differently than previously introduced notions [3], that we will deal with later on. We then introduce strongly safe contract automata, that only accept computations that are in strong agreement.…”

“…It should be noted that a given contract automaton can always be transformed into one that is strongly safe, called its (most permissive) controller, by adapting standard constructions from the supervisory control theory for discrete event systems [8], as done in [3].…”

“…Later on, we recall the notion of agreement on contract automata [3], that only requires the fulfilment of all requests. In a sense, this notion allows a contract automaton to be compositionally placed in an unknown environment that may accept the unmatched offers of the automaton.…”

“…Besides Section 2 on related work, the main new parts concern the notion of agreement just mentioned above, and the new correspondence results for communicating machines with the general semantics, both included in Section 6. Although most of the technicalities on contract automata are inherited from [3], the notion of strong agreement has been introduced here. Finally, we have also revised and simplified some proofs.…”