"Semantic" Web ServicesKarl Aberer - EPFL

Syntax - Semantics

• Separation of concerns for documents: XML – RDF

• XML = exchange format– purpose: communication

• RDF = data model– purpose: conceptualization

• Relationship XML – RDF– 1:RDF -> n:XML (different serializations, formal translation)– 1:XML -> n:RDF (different annotations, interpretation – non-formal)

• How can we carry on this separation for web services ?

Stateless Web Services

• functions addressable and accessible through Web standards– URI's, message interfaces

• f(I):O (syntactic representation given e.g. in WSDL)

• Semantic description (annotation)– f is a resource, thus may belong to some RDF class

• problem: binding semantic to syntactic description

– I, O are resources, thus may belong to some RDF class• problem: as before

– f implements a relationship I-O• problem: characterize its nature, current possibilities in RDF/OIL probably

insufficient

Statefull Web Services

• state accessible through Web-addressable functions• invocation of Web service functions state dependent

• functions have side-effects on the state, in order to model the semantics of the Web service we have to characterize the state– Problems

• how to model state (any decent process model is fine)• how to model semantics of different states (states are resources)• what is the semantics of transitions (a sort of relationship among states ?)• is a "syntactic process model" required, or is this just internal to the Web

service• serialization of the description

State {f1,…,fn}