Information Technology Reference
In-Depth Information
providers. Therefore, we assume that the VTA, the customers, and all other
Web service providers define WSMO descriptions of their respective resources.
The main steps that need to be carried out by the VTA in order to deal with
the request require the following techniques:
Discovery. Out of potentially tens of thousands of Web services available
on the Internet, the VTA needs to determine which of them are usable
for a specific request. Here, a Web service for booking flight tickets from
Innsbruck to Vienna and a Web service for booking hotels in Vienna are
needed.
Composition. The Web services utilized by the VTA need to be composed,
meaning that a suitable execution order of the flight-booking and the hotel
booking Web services needs to be determined. Here, the outputs of the
flight Web service may serve as inputs to the hotel Web service, as the
arrival date at the booked hotel needs to be the same as the arrival date
of the flight.
Mediation. The resources needed to process the request may be heteroge-
neous, which hampers successful interaction. For example, the providers
of the hotel and flight Web services may use different ontologies in their
service descriptions so that information cannot be usefully interchanged,
or the Web services may require incompatible business processes for con-
suming their functionality. These mismatches need to be resolved in order
to allow proper interaction of the Web services, the VTA, and the client.
Execution. After all the necessary Web services have been discovered, com-
posed, and mediated successfully, the VTA needs to execute them. In order
to do so, information interchange as specified in the interfaces of the Web
services should take place automatically.
The subsequent sections illustrate and describe semantically enabled tech-
niques that work on WSMO descriptions of Web services, goals, and media-
tors. It should be noted that the VTA is a placeholder or synonym for generic
Semantic Web service execution environments. As the technology matures,
the VTA will no longer be necessary, because the clients will be able to skip
the intermediary “middle man.” New technologies will allow clients to accom-
plish their goals without relying on the VTA for its mediation and aggregation
service technologies.
9.2 Discovery
WSMO provides a conceptual framework for semantically describing Web ser-
vices and their specific properties. In this section we discuss how WSMO can
be used for service discovery. We provide a proper conceptual grounding by
strictly distinguishing between service and Web service discovery and then
present various techniques for realizing Web service discovery. In order to
cover the complete range of scenarios that can occur in practical applications,
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