Conversation Protocols: A Formalism for Specification and Verification of Reactive Electronic Services

Abstract

This paper focuses on the realizability problem of a framework for modeling and specifying the global behavior of reactive electronic services (e-services). In this framework, Web accessible programs (peers) communicate by asynchronous message passing, and a virtual global watcher listens silently to the network. The global behavior is characterized by a conversation, which is the infinite sequence of messages observed by the watcher. We show that given a Büchi automaton specifying the desired set of conversations, called a conversation protocol, it is possible to implement it using a set of finite state peers if three realizability conditions are satisfied. In particular, the synthesized peers will conform to the protocol by generating only those conversations specified by the protocol. Our results enable a top-down verification strategy where: (1) A conversation protocol is specified by a realizable Büchi automaton, (2) The properties of the protocol are verified on the Büchi automaton specification, (3) The peer implementations are synthesized from the protocol via projection.

Contract Compliance and Choreography Conformance in the Presence of Message Queues

“…In particular, in [FuBS05] the authors present a technique to establish satisfaction of a given property on service conversations from the specifications of the involved services and in [FuBS04] the authors study, given a specification of possible conversations, whether there exists or not a set of services realizing them.…”

Interoperation in Protocol Enactment

“…Fu et al [9] propose conditions for the realizability of protocols-a protocol can be realized if a set of finite agents can generate exactly the conversations in the protocol. Realizability of a protocol is orthogonal to interoperability between agents.…”

Consistency of Service Composition

“…A limitation of this approach is that it is based on a (synchronous) method-invocation model of interaction: as argued in [13], web-service composition languages such BPEL (the Business Process Execution Language [20]) rely on an (asynchronous) message-passing model, which is more adequate for interactions that need to run in a loosely-coupled operating environment. An example of an asynchronous framework is the class of automata-based models proposed in [5,7,11], which is used for addressing a number of questions that arise in choreography, namely the realisability of conversation protocols among a fixed number of peers in terms of the local behaviour generated by implementations of the peers. Our interest is instead in how dependencies on external services that need to be discovered can be reflected in the interface of a peer and in determining properties of such interfaces that can guarantee that the orchestration of the peer can bind to that of a discovered service in a way that ensures consistency of the joint behaviour.…”