Supporting adaptive Web-service orchestration with an agent conversation framework

Service-oriented architecture is emerging as a compelling paradigm for developing Web-based software applications. In this style, the functional components of the system are implemented in various programming languages as network-accessible "services" declaratively specified (in WSDL) and declaratively composed in workflows (using BPEL4WS). Despite this fundamentally distributed conceptualization of service composition, most current middleware assumes that the specification of the service composition is interpreted at run time by a central middleware node. This implies inflexible composition evolution: all parties must be updated concurrently to avoid interaction failures. This paper introduces an intelligent-agent framework that wraps Web services in a conversation layer and is capable of a simple workflow-adaptation function. The conversation layer implements protocols and consults globally shared, declarative policy specifications to resolve conversation failures. Two case studies illustrate this approach.