Composite service discovery, description and invocation

Web Services Technology is an enabling technology which allows heterogeneous software and application systems to interoperate and enables organizations to share data, software and hardware resources over the Internet. The functionalities of heterogeneous software and application systems can be published uniformly as Web services and registered with a service registry. Standard protocols are provided to Internet users to find and invoke registered services. Registered Web services will have limited use unless they can be automatically or semi-automatically combined to form composite services that meet more complex service needs of users. This research investigates several research issues related to service composition and introduces a semi-automatic approach to composite service discovery, description and invocation. It extends the existing Web services model by introducing an Intelligent Service Registry, which interacts with and assists a service requestor through a user interface to specify his/her service requirements, and searches the registered Web services under the service categories selected by the requestor to construct a composite service template(s) for the requestor evaluation and approval. The operations in the discovered and approved template are bound to registered service operations. The resulting composite service is specified in the Web Services Flow Language and used by a Composite Service Processor to invoke the service operations provided by various service providers. In this work, a Service Dependency Graph (SDG) is introduced to capture the input and output relationships among registered Web service operations. It is formally represented as an And-Or graph. An And-Or graph search algorithm is used to construct the composite service template(s) that satisfies a requestor's composite service requirements. The major contributions of this work include (a) an extended Web services model for composite service discovery, description and invocation, (b) the formalization of Service Dependency Graph as an And-Or Graph, (c) an And-Or graph search algorithm for dynamically discovering composite Web services and its performance analysis, (d) an extended WSFL (Web Service Flow Language) for composite service description with constraint specifications, and (e) the architecture and implementation of the Intelligent Service Registry and its integration with an execution engine for the enactment of composite Web services.