Copyright 2007 Digital Enterprise Research Institute. All rights reserved.
www.deri.org
WSMO-Lite:Lightweight Semantic Descriptions for Services on
the Web
Maciej [email protected]
The 5th IEEE European Conference on Web Services (ECOWS2007)November 26-28, 2007, Halle, Germany
Tomas Vitvar, Jacek Kopecký, Maciej Zaremba, Dieter Fensel<[email protected]>
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 "capability" 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 "
?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 .
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 "30"^^ex:euroAmount ;
ex:installationPrice "49"^^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
Q&A
Feedback