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    WSMO-Lite WSMO-Lite Presentation Transcript

    • 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
    • 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
    • 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
    • SAWSDL in a picture
    • 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:
    • 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
    • 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
    • Mapping information semantics to RDF
    • Functional semantics
      • Σ — set of symbols for defining conditions
      • Φpre — precondition
      • Φeff — effect  
      • Represented as &quot;capability&quot; or a category in some taxonomy
    • 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 .
    • 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 .
    • 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
    • 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
    • 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 .
    • 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 .
    • SAWSDL placement of the various semantics
    • 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
    • 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
    • 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?
    • 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
    • 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.
    • Feedback
          • Q&A