SWORD: A Developer Toolkit for Web Service Composition

The formidable problem of automatic or semi-automatic composition of existing Web services is the subject of much current attention. We address a particular subset of this problem with SWORD, a set of tools for the composition of a class of web services including ``information-providing'' services. In SWORD, a service is represented by a rule that expresses that given certain inputs, the service is capable of producing particular outputs. A rule-based expert system is then used to automatically determine whether a desired composite service can be realized using existing services. If so, this derivation is used to construct a plan that when executed instantiates the composite service. As our working prototype and examples demonstrate, SWORD does not require (but could benefit from) wider deployment of emerging service-description standards such as WSDL, SOAP, RDF and DAML. We also distinguish SWORD from some other plausible existing approaches, especially information integration. We show that although SWORD's expressive capabilities are weaker, the abstractions it exposes capture more appropriately the limited kinds of queries supported by typical Web services and thus result in simplicity and efficiency. [Word Count: 7950 words]