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A Web service, as defined by the W3C Web Services Architecture Working Group, is "a software application identified by a URI, whose interfaces and bindings are capable of being defined, described, and discovered as XML artifacts. A Web service supports direct interactions with other software agents using XML-based messages exchanged via Internet-based protocols." 1 Others refine this definition further by requiring the description be a Web Services Description Language (WSDL) document and the protocol be SOAP.
Ferris et al. (Sun,) studied this question.