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Overview of WSMO-Lite: Service Semantics and Technical Solutions for Lightweight Web Services

This lecture outlines the core principles and technical solutions of WSMO-Lite, a lightweight framework for service semantics. It focuses on SAWSDL and its new W3C standards, emphasizing a modularized WSMO approach. The presentation covers key aspects of service semantics including functional, nonfunctional, and behavioral semantics, detailing how these can automate discovery, selection, and composition of web services. Examples illustrate the integration of service models using RDF and OWL, and the effective mapping of services to semantic representations to enhance interoperability in web environments.

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Overview of WSMO-Lite: Service Semantics and Technical Solutions for Lightweight Web Services

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  1. Semantic Web Services Lightweight SWS: WSMO-Lite, MicroWSMO Lecture X – 4th June 2009 Dieter Fensel slides from Jacek Kopecký

  2. Where are we?

  3. Overview Motivation Technical solutions WSMO­Lite Service semantics SAWSDL, WSMO­Lite hRESTS, MicroWSMO 3

  4. Motivation

  5. Motivation • SAWSDL • New W3C standard • Building on SAWSDL, URIs • Assuming RDF, OWL • Lightweight approach • WSMO modularized • Key pieces of service semantics • Simple semantic representation 5

  6. Technical Solutions

  7. WSMO-Lite Ontology: Service Semantics

  8. Overview • WSDL-based service model • SAWSDL-based annotations • Four types of semantics • Expressed in RDF(S) • Attached to the service model

  9. WSDL Simplified Web service input Operation 1 output input Operation 2 output . . . input Operation N output

  10. Service Model in RDFS Service a rdfs:Class . hasOperation a rdf:Property . Operation a rdfs:Class . hasInputMessage a rdf:Property . hasOutputMessage a rdf:Property . hasInputFault a rdf:Property . hasOutputFault a rdf:Property . Message a rdfs:Class .

  11. SAWSDL Properties • On elements of the service model. • modelReference • Pointers to semantics • liftingSchemaMapping • Mapping from WS on-the-wire messages to KR (RDF) • loweringSchemaMapping • Mapping from KR to WS messages

  12. SAWSDL Lifting/Lowering Semanticlevel: Syntacticlevel:

  13. Service Semantics For automation of: • Discovery • Ranking, selection • Composition • Invocation • etc.

  14. Functional What the service does Information model For handling data Incl. lifting/lowering Behavioral How the client talks to the service Nonfunctional Policies, QoS, price, location etc. Types of Service Semantics

  15. Semantics in Service Model F N B I Web service input Operation 1 output input Operation 2 . output . . input Operation N output

  16. Functional Semantics F • For service discovery, composition • Category • Functionality categorization • E.g. eCl@ss, UDDI • Or tagging, folksonomies • Capability • Precondition, Effect • Using WSML rule languages

  17. ex:eCommerceService Category Example wl:FunctionalityClassificationRoot type subclasses ex:TravelReservationService ex:AccommodationReservationService

  18. Category Example (RDF) ex:eCommerceService rdf:type wl:FunctionalityClassificationRoot . ex:TravelReservationService rdfs:subClassOf ex:eCommerceService . ex:AccommodationReservationService rdfs:subClassOf ex:eCommerceService . …

  19. Capability Example ex:RomaHotelReservationPrecondition rdf:type wl:Precondition ; rdf:value """ ?request [ numberOfGuests hasValue ?guests and city hasValue ?city ] memberOf ReservationData and ?guests <= 10 and ?city = 'Roma' """^^wsml:AxiomLiteral .

  20. Nonfunctional Semantics N • For ranking and selection • Not constrained, any ontologies • Example: ex:PriceSpecification rdfs:subClassOf wl:NonFunctionalParameter . ex:ReservationFee rdf:type ex:PriceSpecification ; rdf:value "15"^^ex:euroAmount .

  21. Behavioral Semantics B • For invocation, composition, process mediation • Functionalities on operations • Capabilities, categories • Client selects operation to invoke next • Instead of being strictly guided by an explicit process • Example functional category for operations: WebArch interaction safety

  22. Information Semantics I • For invocation, composition,data mediation • Not constrained, any ontologies • Refer to course Semantic Web (WS)

  23. Service Semantics Summary wl:Ontology wl:FunctionalityClassificationRoot wl:Precondition wl:Effect wl:NonFunctionalParameter Different types of semantics on one component: • E.g. functionality and nonfunc. property on a service > together form a Capability

  24. WSMO-Lite in SAWSDL

  25. WSDL

  26. SAWSDL But: no predefined semantics!

  27. WSMO-Lite in SAWSDL I B F N

  28. WSMO-Lite Example <wsdl:description> <wsdl:types> <xs:schema> <xs:elementname="ReservationRequest" sawsdl:modelReference="&ex;Reservation" sawsdl:loweringSchemaMapping="&ex;ResMapping.xsparql" … /> </xs:schema> </wsdl:types> <wsdl:interfacename="HotelReservations" sawsdl:modelReference= "&ex;AccommodationReservationService"> <wsdl:operation name="searchForRooms" sawsdl:modelReference="&wsdlx;SafeInteraction"> … </wsdl:operation> … </wsdl:interface> <wsdl:service name="RomaHotels" interface="HotelReservations" sawsdl:modelReference="&ex;RomaHotelReservationPrecondition &ex;ReservationFee" … /> </wsdl:description> I I F B F N

  29. hRESTS & MicroWSMO

  30. Recap: RESTful WS • A RESTful Web service is: • A set of Web resources • Interlinked • Data­centric, not functionality­centric • Machine­oriented

  31. Hotel booking service hotel info search results service description payment my bookings confirmation RESTful Web Services

  32. Hypermedia  Operations search(date, city)  list of hotels & rates getHotelDetails(hotel) reserve(rate, creditCard)  confirmationID getConfirmationDetails(confID) listMyBookings()  list of confirmationIDs nouns vs. verbs

  33. hRESTS • "There's usually an HTML page" • There's no WSDL for Web apps • APIs described mostly in text • Identifying machine-readable parts • Service, its operations • Resource address, HTTP method • Input/output data format • hRESTS microformat

  34. Example Description Description of the ACME Hotels service: The operation getHotelDetails is invoked using the method GET at http://example.com/h/{id}, with the ID of the particular hotel replacing the parameter id. It returns the hotel details in an ex:hotelInformation document.

  35. Example HTML <p>Description of the ACME Hotels service:</p> <p> The operation <code>getHotelDetails</code> is invoked using the method <span>GET</span> at <code>http://example.com/h/{id}</code>, with the ID of the particular hotel replacing the parameter <code>id</code>. It returns the hotel details in an <code>ex:hotelInformation</code> document. </p>

  36. Example hRESTS <div class="service"id="svc"> <p>Description of the <span class="label">ACME Hotels</span> service:</p> <div class="operation" id="op1"> <p> The operation <code class="label">getHotelDetails</code> is invoked using the method <spanclass="method">GET</span> at <code class="address">http://example.com/h/{id}</code>, with <span class="input">the ID of the particular hotel replacing the parameter <code>id</code>.</span> It returns <span class="output">the hotel details in an <code>ex:hotelInformation</code> document.</span> </p></div> </div>

  37. Example w/o hRESTS <div class="service" id="svc"> <p>Description of the <span class="label">ACME Hotels</span> service:</p> <div class="operation" id="op1"> <p> The operation <code class="label">getHotelDetails</code> is invoked using the method <span class="method">GET</span> at <code class="address">http://example.com/h/{id}</code>, with <span class="input">the ID of the particular hotel replacing the parameter <code>id</code>.</span> It returns <span class="output">the hotel details in an <code>ex:hotelInformation</code> document.</span> </p></div> </div>

  38. hRESTS • HTML for RESTful Service Description • Introduces the service model structure • service (+ label) • operations (+ address, method) • input, output • Can also be in RDFa • Basis for extensions: • MicroWSMO adds semantic annotations

  39. MicroWSMO • Extends hRESTS • model for model references • lifting, lowering • Applies WSMO-Lite semantics

  40. MicroWSMO <div class="service" id="svc"> <p><span class="label">ACME Hotels</span> is a <a rel="model"href="…/ecommerce/hotelReservation"> hotel reservation</a> service.</p> … <div class="operation" id="op1"><p> … <span class="input">A particular hotel ID replaces the param <a rel="model"href="…/onto.owl#Hotel"><code>id</code></a> (<arel="lowering"href="…/hotelID.xslt">lowering</a>). </span>. … </p></div> </div>

  41. Semantics Implied in Web • Hypermedia  behavioral semantics • Links become available through interaction • Uniform interface  functional semantics • GET, PUT, DELETE have known effects • GET is safe, PUT and DELETE idempotent • Self-description  information model • Operation output data can specify what it is • GRDDL, other semantic annotations

  42. Conclusions

  43. Conclusions • Building on SAWSDL • Both for WS-* and RESTful services • Bottom-up annotations • Based on tech already known by WS people • Modular descriptions • Only use what you need

  44. Further Developments • Adding WSMO-Lite and MicroWSMO support to WSMX • Tool support for service annotation • Standardization of WSMO-Lite

  45. References • SAWSDL: http://w3.org/TR/sawsdl • WSMO-Lite: http://cms-wg.sti2.org/TR/d11 • hRESTS & MicroWSMO: http://cms-wg.sti2.org/TR/d12 • RDF: http://w3.org/TR/rdf-primer • RDFS: http://w3.org/TR/rdf-schema • REST: http://en.wikipedia.org/wiki/REST • Includes RESTful Web services • eCl@ss: http://www.eclass-online.com

  46. Next Lecture

  47. Questions?

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