Conversation Errors in Web Service Coordination Run-time Detection and Repair.pdf

Conversation Errors in Web Service Coordination: Run-time Detection and Repair Warren Blanchet, Renée Elio, and Eleni Stroulia Department of Computing Science University of Alberta {blanchet, ree, stroulia}@cs.ualberta.ca Abstract Organizations that own web services participating in a workflow composition may evolve their components independently. Service coordination can fail when previously legal messages between independently changing, distributed components become illegal because their respective workflow models are no longer synchronized. This paper presents an intelligent-agent framework that wraps a web service in a conversation layer and a simple workflow-adaptation function. The conversation layer implements protocols and consults globally shared, declarative policy specifications to resolve interaction failures. The framework allows agents to resolves various model mismatches that cause interaction errors, including changes to required preconditions, partners, and expected message ordering. Implications of this distributed approach to web service coordination are also discussed. 1. Introduction One of the appealing elements of web service composition is its distributed conceptualization: functional components of a system are implemented as network-accessible “services” declaratively specified (in WSDL) and declaratively composed (in BPEL4WS). However, most of the available middleware environments that support this composition assume that the coordination specification, which defines conversation controllers, is interpreted by a central middleware node. This poses some interesting issues for bottom-up Enterprise Application Integration, in which the various organizations that own the services participating in the workflow may evolve their services independently. The question then becomes “how should a composition evolve with its independently changing, constituent services?”. For example, suppose that Organization A adds new preconditions that must be satis