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Service Ontologies

Posted by Aditya Thatte on December 10, 2008

Ontologies classifying and describing services are called service ontologies. The existing WSDL interface describes a service by specifying operation name, inputs required, output of the service and its target address for invocation. Human intervention is required in this loop since the current architecture only addresses the syntactical aspects of Web services and lacks choreography mechanisms.

Service ontologies supplements the WSDL interface, adding knowledge required to enable automatic discovery, invocation and composition of web services. The idea is to annotate web services, enabling the automation of the web service life cycle.

The existing conceptual models for describing services are OWL-S, WSMO, WSDL-S, SWSF, SAWSDL.

For example, the OWL-S service ontology is classified into three categories : profile, model, grounding as shown in the diagram. The service component is actually an instance of the service and is linked to the profile, model, grounding by different properties. The profile is an advertisement of what the service does i.e what the service offers in terms of functionality. It considers input, output, preconditions, effects ( IOPE ).

The input specifies the actual input required for invoking the web service, output specifies the actual output the client gets or expects. Preconditions indicates the conditions that need to be satisfied for the successful execution of the web service. The effect describes the state of the web service after its execution.

The service model describes how the service works in order to achieve its functionality. It describes atomic processes, composite processes and the message choreography involved in invoking the web service. Atomic processes are the ones, that undergo straight forward execution requiring standard input, whereas composite processes are the ones which involve combination of different services.

Service grounding illustrates as to how the service can be accessed.It describes the network protocols, data exchange formats, required to invoke the web service.

Like OWL-S, the other models also address the semantic nature of web service descriptions thereby making an effort to automate the web service life cycle.

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