AND/OR Graph and Search Algorithm for Discovering Composite Web Services

This paper presents a formalization of the Web Service composition problem as a search problem in an AND/OR graph, and a search algorithm for searching the graph to identify composite service(s) that satisfies a Web Service request. Given a service request that only can be satisfied by a composition of Web Services, we identify the service categories that are relevant to the request and dynamically construct an AND/OR graph to capture the input/output dependencies among the Web Services of these service categories. The graph is modified, based on the information provided in a service request. The search algorithm then is used to search the modified AND/OR graph for a minimal and complete composite service template that satisfies the service request. The algorithm can be applied repeatedly to the graph to search for alternative templates until the result is approved by the service requester. We have evaluated the algorithm both analytically and experimentally, and the experiment results are presented.