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]