Using Virtual Services to Bridge the Semantic Gap

In cloud computing, data, software, and hardware are wrapped as services, which are made available on demand. Given a demand, the associated services need to interact with each other to fulfill the task. As a result, service reuse and composition are inevitable. The current prevailing Web service composition paradigms follow the bottom-up manner, i.e., the concrete services are physically constructed first. Then, some mechanisms are applied to raise the level of abstraction so that the service composition process can be performed at a higher level. However, such paradigms are very fragile. In the event that some semantic contents are missing, the composition will fail even though the majority of services may be available. In this paper, we present a service composition approach that is a combination of the bottom-up and top-down strategies. In terms of bottom-up, our approach follows the current service composition methods and tries to use existing Web services to meet the given demand. If the composition process fails, virtual services are proposed by the composer to bridge the semantic gap so that the composition process will continue. Virtual services may not have physical counterparts and may exist only conceptually. However, it provides a high-level specification for a service that is missing. This is a typical top-down manner, i.e., by following the specification, developers and designers will have clear ideas regarding what to develop to meet the given demand. Therefore, our approach can further improve the level of service reuse.