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XML Schema Ad Hoc Ontology
In this approach, an ad-hoc ontology is automatically generated from the
schema of the XML messages according to a conceptual mapping between
the XML metamodel and the ontological metamodel. Along with this ad-
hoc ontology, a set of mapping rules is also generated for the lifting/lowering
transformations between the XML messages and instances of the generated
ontology.
If the designer of the semantic description finds this generated ontology
suitable for describing a particular Web service, this grounding can be fully
automatic. On the other hand, if the generated ad hoc ontology cannot be
used, grounding involves an additional transformation between instances of
the ad hoc ontology and instances of the target ontology used by the service
description. This transformation step uses ontology mediation.
Similarly to the XSLT approach, the ad hoc ontology approach has the
benefit of reusing existing transformation technologies (ontology mediation in
this case). However, the disadvantage is that the generated ad hoc ontology is
not a
native
ontology (it is structured as a restrictive schema for data valida-
tion, as opposed to a descriptive ontology for knowledge representation), and
this ontology can lack or even misrepresent semantics that are only implied
in the XML. This can complicate the task of mediating between the ad hoc
ontology and the target ontology describing the service, similarly to the way
that
non native
XML data can complicate an XSLT transformation.
Because WSMO puts a heavy focus on mediation, WSMO grounding is
currently being developed in the direction of this approach, using WSMO
ontology mediation for the transformations.
Direct-Mapping Language
Although we are not aware of any work in this direction in either of the
Semantic Web service frameworks, we envision a third option that transforms
between the XML data and the ontological data directly, using a specific
transformation language.
While a new transformation language would have to be created, it could
be optimized for the common transformation patterns between native onto-
logical data and native XML. Manually created mappings would be simpler
to understand, create and manage than in the previous approaches. If the
disadvantages of the other approaches prove substantial, then development of
such a new language should be considered.
9.5.3 Behavior Grounding
The choreography description allows the client to know what messages it can
send or receive at any specific point during interaction with a service. Because
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