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1. WSDL-S aims to build upon existing Web service standards and promotes
an upwardly compatible mechanism for adding semantics to Web services.
2. Annotations should be impartial with respect to the representation lan-
guage for the semantic model. Consequently, WSDL-S does not prescribe
which semantic representation language should be used.
3. Support for XML Schema datatype annotations needs to be added to the
XML Schema, as this is the most important data definition format in the
realm of Web services.
The third item, i.e. closing the gap between WSDL message descriptions
(inputs/outputs) in terms of XML Schema and their semantic counterparts,
is precisely the problem addressed in WSMO (and OWL-S) in the
grounding
component. However, WSDL-S differs fundamentally in being linked to WSDL
and not defining semantic annotations separately. Instead, WSDL-S links from
WSDL to the semantic description in terms of ontological concepts which are
defined externally.
In addition, attributes for referencing mappings between XML Schema
complex types and the corresponding ontological concepts are included in
WSDL-S. In its specification, WSDL-S exemplifies XSLT and XQuery as pos-
sible technologies to define such lifting/lowering from XML Schema to the
ontological level.
8.3.1 Language
WSDL-S does not fix a specific formalism for semantic descriptions. WSML,
OWL, and UML are mentioned as examples of formalisms that could be
adopted. Remarkably, unlike the other frameworks described so far, WSDL-
S fixes the underlying service technology (referred to as “grounding” in the
other formalisms) to WSDL by definition.
8.3.2 Relationship Between WSDL-S and WSMO
WSDL-S, with its minimalist approach can be viewed as orthogonal to
WSMO. It can even use to annotations in WSML for defining conditions,
etc. in its annotations or references to WSMO descriptions.
We have already mentioned that WSDL-S does not claim to be a fully-
fledged description framework/ontology, but rather simply adds some useful
attributes to WSDL's XML tags in order to reference semantic annotations.
All the referenced concepts such as message types, operation preconditions,
effects, and service categories can likewise be annotated in WSML/WSMO.
Unlike WSMO, WSDL-S does not clearly establish how requests should
be defined. As we move towards a standard Semantic Web architecture, the
complete impartiality of WSDL-S with respect to the language used for defin-
ing semantic annotations might be criticized. Without a certain degree of
commitment to a specific language, or, at the very least, a definition of how
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