Copyright 2007 Digital Enterprise Research Institute. All rights reserved.

www.deri.org

WSMO-Lite:Lightweight Semantic Descriptions for Services on

the Web

Maciej Zarembamaciej.zaremba@deri.org

The 5th IEEE European Conference on Web Services (ECOWS2007)November 26-28, 2007, Halle, Germany

Tomas Vitvar, Jacek Kopecký, Maciej Zaremba, Dieter Fensel<first.last@deri.org>

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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

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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

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SAWSDL in a picture

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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:

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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

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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

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Mapping information semantics to RDF

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Functional semantics

Σ — set of symbols for defining conditions Φpre — precondition Φeff — effect

  Represented as "capability" or a category in some

taxonomy

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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 .

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Example capability

ex:VideoOnDemanSubscription rdf:type lso:Capability ; lso:hasPrecondition "

?customer[hasConnection hasValue ?connection] memberOf Customer and ?service[requiresBandwidth hasValue ?x] memberOf Service and ?connection[providesBandwidth hasValue ?y] memberOf NetworkConnection and ?y > ?x "^^wsml:AxiomLiteral . lso:hasEffect "

?bundle[hasService hasValue ?service and hasConnection hasValue ?connection] memberOf Bundle

"^^wsml:AxiomLiteral .

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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

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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

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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 .

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Non-functional semantics

Due to lack of common model, no constraints in WSMO-Lite

ex:VideoOnDemandPrice rdf:type ex:PriceSpecification ; ex:pricePerChange "30"^^ex:euroAmount ;

ex:installationPrice "49"^^ex:euroAmount .

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SAWSDL placement of the various semantics

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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

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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

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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?

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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

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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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Q&A

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