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WSMO-Lite: Lightweight Descriptions of Services on the Web


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WSMO-Lite: Lightweight Descriptions of Services on the Web

  1. 1. WSMO-Lite: Lightweight Semantic Descriptions for Services on the Web Tomas Vitvar, Jacek Kopecký, Maciej Zaremba, Dieter Fensel <> Maciej Zaremba maciej . zaremba The 5 th IEEE European Conference on Web Services (E COWS 2007) November 26 - 28 , 2007, Halle , Germany
  2. 2. Problem statement <ul><li>Semantic Web Services (SWS) automation </li></ul><ul><ul><li>needs semantic descriptions of Web services </li></ul></ul><ul><li>WSMO, OWL-S etc... </li></ul><ul><ul><li>top-down models </li></ul></ul><ul><ul><li>independent from... Web services </li></ul></ul><ul><ul><li>grounding as a link to WSDL </li></ul></ul><ul><li>W3C has SAWSDL </li></ul><ul><ul><li>making WSDL the base for SWS descriptions </li></ul></ul><ul><li>WSMO-Lite </li></ul><ul><ul><li>lightweight semantic descriptions for Web services </li></ul></ul><ul><ul><li>based on analysis of the required semantics </li></ul></ul>
  3. 3. To refresh: WSDL structure <ul><ul><li>Interface is a set of operations </li></ul></ul><ul><ul><li>Operation represents a single simple message exchange </li></ul></ul><ul><ul><li>Message is an XML element </li></ul></ul><ul><ul><li>Binding says how messages go on the wire </li></ul></ul><ul><ul><li>Service has a number of endpoints and a single interface </li></ul></ul><ul><ul><li>Endpoint says where the service lives and specifies a binding </li></ul></ul>
  4. 4. SAWSDL in a picture
  5. 5. SAWSDL in a few words <ul><li>Extends WSDL with pointers to semantics </li></ul><ul><li>Model references point to semantic concepts </li></ul><ul><li>Schema mappings point to data transformations for lifting, lowering: </li></ul>
  6. 6. What semantics are needed? <ul><li>Information </li></ul><ul><ul><li>to understand service inputs and outputs </li></ul></ul><ul><li>Functional </li></ul><ul><ul><li>to know what a service does </li></ul></ul><ul><li>Non-functional </li></ul><ul><ul><li>any other semantics useful for ranking </li></ul></ul><ul><li>Behavioral </li></ul><ul><ul><li>to know how to communicate with the service </li></ul></ul>
  7. 7. Information semantics <ul><li>C — set of classes </li></ul><ul><ul><li>unary relations </li></ul></ul><ul><li>R — set of relations </li></ul><ul><ul><li>binary and higher arity </li></ul></ul><ul><li>Represented as RDFS/OWL ontologies </li></ul><ul><li>E — extensional definitions </li></ul><ul><ul><li>explicit instances of classes, relations </li></ul></ul><ul><li>I — intensional definitions </li></ul><ul><ul><li>axioms, rules </li></ul></ul>
  8. 8. Mapping information semantics to RDF
  9. 9. Functional semantics <ul><li>Σ — set of symbols for defining conditions </li></ul><ul><li>Φpre — precondition </li></ul><ul><li>Φeff — effect   </li></ul><ul><li>Represented as &quot;capability&quot; or a category in some taxonomy </li></ul>
  10. 10. WSMO-Lite ontology for capability lso:Capability rdf:type rdfs:Class . lso:hasPrecondition rdf:type rdf:Property . rdfs:domain lso:Capability ; rdfs:range lso:Axiom . lso:hasEffect rdf:type rdf:Property ; rdfs:domain lso:Capability ; rdfs:range lso:Axiom . lso:Axiom rdf:type rdfs:Class .
  11. 11. Example capability ex:VideoOnDemanSubscription rdf:type lso:Capability ; lso:hasPrecondition &quot; ?customer[hasConnection hasValue ?connection] memberOf Customer and ?service[requiresBandwidth hasValue ?x] memberOf Service and ?connection[providesBandwidth hasValue ?y] memberOf NetworkConnection and ?y > ?x &quot;^^wsml:AxiomLiteral . lso:hasEffect &quot; ?bundle[hasService hasValue ?service and hasConnection hasValue ?connection] memberOf Bundle &quot;^^wsml:AxiomLiteral .
  12. 12. Capability restriction <ul><li>F1 is a restriction of F2 </li></ul><ul><li>A discovery mechanism that discovers F1 will also discover F2 </li></ul><ul><li>Put F2 on an interface, F1 on a service, then interface discovery is a filter for service discovery </li></ul><ul><li>And the same with WSDL 2.0 interface extension </li></ul>
  13. 13. Behavioral semantics <ul><li>It's a Chi, not an X </li></ul><ul><li>Σ — set of symbols for defining rules </li></ul><ul><ul><li>incl. dynamic symbols for input and output </li></ul></ul><ul><li>L — set of rules: r cond -> r eff   </li></ul><ul><li>Represented as operation capabilities or as explicit choreography </li></ul>
  14. 14. WSMO-Lite ontology for choreography lso:Choreography rdf:type rdfs:Class . lso:hasInClass rdf:Type rdfs:Property ; rdfs:domain lso:Choreography ; rdfs:range rdfs:Class . lso:hasOutClass rdf:Type rdfs:Property ; rdfs:domain lso:Choreography ; rdfs:range rdfs:Class . lso:hasRule rdf:Type rdfs:Property ; rdfs:domain lso:Choreography ; rdfs:range lso:Rule . lso:Rule rdf:Type rdfs:Class .
  15. 15. Non-functional semantics <ul><li>Due to lack of common model, no constraints in WSMO-Lite </li></ul><ul><li>ex:VideoOnDemandPrice rdf:type ex:PriceSpecification ; ex:pricePerChange &quot;30&quot;^^ex:euroAmount ; ex:installationPrice &quot;49&quot;^^ex:euroAmount . </li></ul>
  16. 16. SAWSDL placement of the various semantics
  17. 17. Consistency and completeness rules <ul><li>Completeness of information semantics annotation: </li></ul><ul><ul><li>every input and output message of every operation must be annotated with pointers and mappings to ontology </li></ul></ul><ul><li>Consistency of functional semantics annotation: </li></ul><ul><ul><li>a service capability (if any) must be a restriction of the service's interface capability (if any) </li></ul></ul><ul><ul><li>an interface capability (if any) must be a restriction of an extending interface's capability (if any) </li></ul></ul><ul><li>Completeness of functional/behavioral semantics annotations: </li></ul><ul><ul><li>if an operation does not have a capability, it must be part of the interface's choreography </li></ul></ul><ul><ul><li>every choreography must be consistent with some capability of the same service/interface </li></ul></ul><ul><li>Completeness of behavioral/information semantics annotations: </li></ul><ul><ul><li>each choreography in /out must be grounded in an operation in /out </li></ul></ul>
  18. 18. Related work <ul><li>A recent ISWC paper (D. Martin, M. Paolucci, M. Wagner: „Bringing Semantic Annotations to Web Services: OWL-S from the SAWSDL Perspective”) about OWL-S from SAWSDL perspective </li></ul><ul><ul><li>presented from OWL-S perspective, but results similar </li></ul></ul>
  19. 19. Open discussion points <ul><li>Capability with preconditions and effects may not be necessary </li></ul><ul><ul><li>in connection with instance-based discovery, simple service discovery based on taxonomy could suffice </li></ul></ul><ul><li>Choreography can be represented only as operation capabilities </li></ul><ul><ul><li>still debating the value of explicit choreography — detached from operations </li></ul></ul><ul><li>Name </li></ul><ul><ul><li>if it doesn't quack like a duck, can we call it duck-lite? </li></ul></ul>
  20. 20. Conclusions on WSMO-Lite <ul><li>A simple ontology in RDFS </li></ul><ul><ul><li>Because RDFS is perceived as the easiest (lighter than OWL-Light) </li></ul></ul><ul><ul><li>We don't really need much reasoning </li></ul></ul><ul><ul><li>Rules may be necessary for capabilities and choreographies </li></ul></ul><ul><li>Inspired by WSMO </li></ul><ul><ul><li>... but no overarching model, instead pieces that fit in SAWSDL </li></ul></ul><ul><ul><li>WSDL provides the overarching model </li></ul></ul><ul><li>Guided by a formal model of four types of semantics </li></ul>
  21. 21. Resources <ul><li>SAWSDL specification </li></ul><ul><li>RDFXSLT for lifting and lowering using XSLT </li></ul><ul><li>D. Martin et al.: Bringing Semantic Annotations to Web Services: OWL-S from the SAWSDL Perspective . At the 6th Int'l Semantic Web Conference , ISWC 2007, Busan, South Korea. </li></ul>
  22. 22. Feedback <ul><ul><ul><li>Q&A </li></ul></ul></ul>