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Fig. 9.4.
Matchmaking notions for semantically enabled discovery
We have presented a conceptual model for service discovery which avoids
unrealistic assumptions and is suitable for a wide range of applications. One of
the key features of this model is the explicit distinction between the notions
of Web services and services. We have outlined various approaches to the
discovery of Web services, with various requirements on the description of
Web services and the discovery goal itself. We have concluded by emphasizing
the advantages of our favored approach: semantic-based Web service discovery.
9.3 Mediation
Owing to its design principle of decentralization, the World Wide Web is
a network of decoupled, independently working computers. This makes the
Web heterogeneous by nature: people create Web sites and applications inde-
pendently, resulting in mismatches that hamper information interchange and
interoperability. In consequence, the Semantic Web will be heterogeneous as
well. The techniques for handling and resolving mismatches that hamper in-
teroperability of Web resources require mediation, a central pillar of the next
generation of Web technologies.
In the early 1990s, Wiederhold proposed so-called
mediator-oriented ar-
chitectures
for handling heterogeneities in IT systems [135]. In these architec-
tures, mediators are integrated components capable of dynamically handling
heterogeneities that hamper successful interoperation of system components.
For generic, application-independent mediation, the mechanisms for mismatch
resolution need to work on a structural level, based on declarative resource
descriptions. One of the merits of the Semantic Web is that resources carry
semantic descriptions, which allows mediation techniques to be defined on
a semantic level. Whereas OWL-S [87] defines an ontology for semantically
describing Web services yet remains orthogonal to mediation [107], WSMO
identifies mediation as a first-class citizen and, consequently, defines mediators
as a core element of Semantic Web services.
In order to attain a mediator-oriented architecture in accordance with
Wiederhold's conception, the WSMO mediation model presented in [122] dis-
tinguishes two dimensions: (1)
mediation techniques
for resolving various kinds
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