This position paper represents my attempt to clarify what constraints on emergent web services technology would benifit the semantic web. The "position" presented here proposes design constraints that benefit many other communities as well, by encouraging a clear specification of the underlying model. I hope that web services leverage off semantic web experience in describing models.
For the purposes of data availability and re-use, the semantic web and others would benifit from a well-described data model and vocabulary. It would be ideal if an emergent activity or working group kept serialization orthogonal to the abstract data structures. Uche Ogbuji's article Supercharging WSDL with RDF Managing structured Web service metadata desribes a serialization of the wsdl model in RDF and motivations to do so. I naturally support this, but feel that a rigorously described model, regardless of serialization, will promote use of this data in RDF as well as other protocols and model serializers.
Defining a data structure requires defining the members of the structure and the relationships between them. Many XML protocols leverage off namespaces to uniquely define the tags in an XML document. RDF goes a step furthur to use the URIs in namespaces and elements to define the semantics these tags represent. A useful web services framework will define its underlying data structure in terms of URIs for greatest portability and encapsulatability.
If a web services protocol does not rely on the service description to be a single document, auxilliary documents could be used to extend the service after the initial description has been published. These could be used by the initial service architect to revise the protocol, or by third parties to re-use and extend the service.
Versatile applications could publish multiple descriptions, similar to Java classes advertising multiple interfaces. Distributed service descriptions enable an service provider to reference multiple descriptions, leveraging off infrastructure designed to work with any of the descriptions.
Web service protocols will likely express relationships between classes of services, including that one services is an extension of another. The semantic web languages express these semantics in predicates that are supported by the infrastructure. This frees applications from implementing these details and assures that the applications may depend on other parties to support hierarchy, even if these parties are not aware of the web services protocols.