WSMO-Lite provides lightweight semantic descriptions for web services based on an analysis of the minimum semantics needed. It defines an RDFS ontology to represent information, functional, behavioral, and non-functional semantics in a way that maps to SAWSDL annotations. WSMO-Lite semantics include capabilities to describe what a service does, and choreographies to describe how it is used through message exchange.

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.

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