Compositionality of handlers on intermediate servers in a web service architecture

This research addresses the problem of inter-operability among different components in a Web service architecture on the Internet. "Message Handlers" are pieces of code that intercept the message between clients and services in order to create/modify different pieces of the message, or to perform a processing task. For several reasons, such as management, reusability, optimization, routing, providing value-added services and transformations, it might be desirable to have chains of handlers on intermediate servers on the path between the client and the server; however, automatic selection of the set of handlers to be executed and their order of execution is still a problem. We try to solve this problem based on the type of the messages that are sent by the clients and the expected server input type. We leverage two algorithms based on formal language theory in order to solve the handler composition problem. Our case studies show how our approach could help in solving the problem of schema migration and version incompatibility in a large system such as eBay.Science, Faculty ofComputer Science, Department ofGraduat

Interface Composition for Web Service Intermediaries

Abstract. The use of XML as a format for message exchange makes Web services well suited for composition of heterogeneous components. However, since clients must manage differences in message schemas between services, interoperability is still a significant problem. Interoperability currently can be supported through the use of transformations provided by a Web service intermediary. However, intermediary technologies do not provide a way for clients to reason about the composition of services and intermediaries. We propose an approach to provide clients with an interface composed of schema information from a Web service and an intermediary. Composition is performed by applying rewriting rules, defined by the intermediary, to the server interface schema. This new interface takes into account what transformations are available at an intermediary. The advantage of the approach is that clients can continue to benefit from codegeneration and static type-checking offered by interface definition languages such as WSDL; while still making use of the flexibility offered by intermediary transformations. We provide the algorithmic details of composition, including a proof of correctness and an upper bound on complexity. We demonstrate the approach in the context of a Web service composition of three publicly available Web services.