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WSMO-Lite: Lightweight Descriptions of Services on the Web

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