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for Web services that can be used to buy tickets. And service discovery is
about checking whether the ticket sellers offering such Web services can really
provide the requested ticket. We do not think that complete, correct descrip-
tions of all the services offered by a Web service are a realistic expectation;
Web services would then be no longer necessary (at least not the discovery
process). We wonder whether logical reasoning would scale under these condi-
tions where the execution of an e
cient program accessed via the Web service
would be simulated by reasoning over its semantic annotation.
Alternatively, one might assume to directly query the Web service during
the Web service discovery process. However, this may lead to network and
server overload, and it makes a very strong assumption: in addition to data,
protocol, and process mediation, the Web service must first be established be-
fore the discovery process can take place. In general, we do not think that this
is a realistic assumption; however, we defer a more detailed discussion to Sec-
tion 9.3. As a result, we think it is essential to distinguish between Web service
discovery and service discovery in order to come up with a workable approach
that scales and makes realistic assumptions in a pragmatic environment. In
summary:
•
Web service discovery is based on matching abstracted goal descriptions
with semantic annotations of Web services. This discovery process can
happen only on an ontological level, i.e. it can rely only on conceptual
and reusable data. For this, to be possible, two processes are required:
(1) the concrete user input has to be generalized to more abstract goal
descriptions, and (2) the concrete services and their descriptions have to
be abstracted to the classes of services that a Web service can provide.
We believe that this twofold abstraction is essential for lifting Web service
discovery to an ontological level, which is a prerequisite for a scalable and
workable solution.
•
Service discovery is based on the use of Web services for discovering actual
services. Web service technology provides automated interfaces to the in-
formation provided by software artifacts that is needed to find, select, and
eventually buy a real-world service or simply find a piece of information
that somebody is looking for. Service discovery requires strong mediation
and wrapping, since the specific needs of the choreography of a Web service
must be met in order to interoperate with it. Note that automation of ser-
vice discovery defines significantly higher requirements of mediation than
does that of Web service discovery, since protocol and process mediation
is also required.
and refer to the Web service interface and the accessed software artifact as one
entity.
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