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Semantic Descriptions for RESTful ServicesSA-REST by Knoesis Service Research Lab
Tomas [email protected]
WSMO Phone ConferenceJanuary 09, 2008
Tomas Vitvarhttp://www.vitvar.com
REST, mashups
• REpresentational State Transfer (REST) services -- great success in web content integration (mashups)o RESTful -- XML messaging and HTTPo no service contracts (when not used in combination with
WSDL)• RESTful services -- basis for mashups
o hard to create mashups manually o frameworks (mashup editors) supporting mashups
development: Yahoo! pipes, IBM QEDwiki, Google Mashup Editor (-) limited to internal company services (-) limited to output of RSS or Atom (-) data integration problem
Semantics in Services
• Two layers1.Semantic Model - WSMO, WSMO-Lite, OWL-S, ...2.Linking of the semantic model with technology for
communication and invocation (e.g. WSMO grounding, SAWSDL annotations)
• What we haveo WSMO + WSMO grounding for WSDL (D24.2)o WSMO-Lite + SAWSDL for WSDL (D11)
Representation of RESTful services
• no service contracts (when not specified using WSDL)• description usually embedded in web pages in HTML• Challenge: how to annotate RESTful services available in
HTML -> obvious solution: RDFa, GRDDL (adding meta-data to a human readable text so that a machine can glean semantics)
• What SA-REST proposes[1, 2, 3]o any semantic model (but mostly ontology) (encourages
OWL or RDF) + RDFa or GRDDLo building on the idea of WSDL-S (and SAWSDL) --
borrowing the modelReference annotation (linking non-semantic and semantic concepts)
SA-REST mechanism (RDFa)
• semantic annotations in RDFa in HTML describing the service
• Triple: o subject -- the URL at which the service is invokedo predicate -- sarest:input, sarest:output, sarest:operation,
sarest:lifting, sarest:lowering, sarest:fault (sarest prefix is the alias for the sarest namespace)
o object -- URI or URL of a resource (semantic concept, etc.) depending on the predicate
SA-REST example (RDFa)
SA-REST document for a Web service to search for houses on craigslist.com
SA-REST and GRDDL
• SA-REST allows to use GRDDL to attach annotations• Basic steps
o annotate the HTML page with microformato add GRDDL profile attribute to <head> (it tells the agent
the page is annotated with GRDDL)o link to <head> element pointing to translation document
URL
• Requirement: the resulting data from GRDDL transformation must conform to the RDF triples described by RDFa annotation.
Conclusions
• SA-REST is the first step in using RDFa/GRDDL for enhancing RESTful services with semantics
• SA-REST does not preclude any semantic model (in this way it is very similar approach to SAWSDL/WSDL-S)
• SA-REST recommends to use standard languages (OWL, RDF), plus RDFa, GRDDL
• SA-REST is "just" an annotation mechanism (like SAWSDL)• WSMO-Lite/WSMO can be used as the semantic model on
top of SA-REST (would require more specifications)• Relevant work: Semantic Web Pipes (work done by Axel in
DERI Galway)• Discussion in W3C SWS-testbed XG
References
SA-REST done by Knoesis Service Research Lab:
[1] http://knoesis.wright.edu/research/srl/standards/sa-rest/
[2] http://dx.doi.org/10.1109/ICOSC.2007.4338383
[3] http://doi.ieeecomputersociety.org/10.1109/MIC.2007.133
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