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RDF primer text for 5.15: RDF mapping

From: Jacek Kopecky <jacek.kopecky@deri.org>
Date: Thu, 24 Mar 2005 17:27:27 +0100
To: WS-Description WG <www-ws-desc@w3.org>
Cc: David Booth <dbooth@w3.org>
Message-Id: <1111681647.3379.71.camel@Kalb>
Hi all, 
below is a first cut of the text for primer section 5.15 - Mapping to
RDF and Semantic Web, created by me and Bijan.
Jacek

5.15 Mapping to RDF and Semantic Web

WSDL is a language designed primarily with XML syntax. While XML is
almost universally understood, it has several issues: 


      * Composing two XML files into one depends on the languages: we
        can be able to merge two WSDL files with the same
        targetNamespace into one (as long as there are no conflicts),
        but WSDL doesn't provide for composing two different documents
        in different namespaces into a single XML document. 
      * Extending XML languages with other XML languages depends on the
        languages again. WSDL is extremely extensible, but the meaning
        of every single extension in WSDL has to be defined - putting a
        piece of XMI (XML format for UML) as extension in WSDL may have
        different meaning from putting XMI into an XHTML document.
        Therefore XML-based extensibility has very high cost if many
        languages are involved. 
      * Similarly, extending another XML language with pieces of WSDL,
        while possible, has to be defined for all the possible
        destinations. Putting a WSDL interface element into a UDDI
        registry may mean a different thing from putting that interface
        element into an XHTML document. 
      * Finally, the meaning of pieces of WSDL is undefined by the WSDL
        specification; while an interface element can form a single XML
        document, it is not a WSDL document and the meaning of such an
        element is largely undefined. 


Application that require such levels of composability (or
decomposability) are increasingly being based on RDF, a graph-based
knowledge representation language, and Web Ontology Language (OWL),
which can be thought of as an advanced schema language for RDF. The
Semantic Web is envisioned as an interlinked collection of such
applications, together working on the whole scale of the World Wide
Web. 

The document WSDL 2.0: Mapping to RDF describes how WSDL constructs are
expressed in RDF using classes of resources (described with an ontology
expressed in OWL) and assertions over individual resources. Effectively,
a WSDL document represented in RDF can be easier extended with arbitrary
RDF assertions and the WSDL information can easier be ascribed to
arbitrary other knowledge. 



5.15.1 RDF representation of WSDL

As RDF represents knowledge using resources and relationships between
them, we need to turn WSDL concepts into this model. 


     1. First, all components in WSDL (like Interfaces, Operations,
        Bindings, Services, Endpoints etc., including extensions) are
        turned into resources identified with the appropriate URIs
        created according to Appendix C. 
     2. Further things are represented as resources: 
             1. Element declarations gathered from XML Schema (or
                similarly, other components from other type systems)
             2. Message content models
             3. Message exchange patterns (the URI identifying the MEP
                is the URI of the resource) 
             4. Operation styles (similarly to MEPs, the URI of an
                operation style is the URI of the resource) 
     3. All the resources above are given the appropriate types using
        rdf:type stataments (an interface will belong to the class
        Interface and an operation within an interface will belong to
        the class InterfaceOperation, for example) 
     4. All relationships in WSDL (like Operation belonging to an
        Interface and having a given operation style) are turned into
        RDF statements using the appropriate properties (here, operation
        and operationStyle) 


todo: as an example, an RDF translation of a (snippet of a) simple WSDL
file from earlier in the primer 
Received on Thursday, 24 March 2005 16:28:04 GMT

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