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semantically equivalent to OWL DL. However, there is a major difference be-
tween ontology modeling in WSML and ontology modeling in OWL. WSML
uses an epistemology which abstracts from the underlying logical language,
whereas OWL directly uses description logic's epistemology. Also, in con-
trast to OWL, WSML makes a separation between conceptual modeling for
the nonexpert user and logical modeling for the expert user. Arguably, these
properties could make WSML easier to use as an ontology language. This
is, however, merely a conjecture and would require extensive user testing to
verify its correctness.
Since WSML-Flight and WSML-Rule are based on the logic programming
paradigm rather than the description logic paradigm, their expressiveness is
quite different from that of OWL. Advantageously, WSML-Flight and Rule
allow chaining over predicates and nonmonotonic negation, but do not allow
classical negation, full disjunction or existential quantification. We conjecture
that both the description logics and logic programming paradigms are useful
on the Semantic Web (see [70]). With WSML, we capture both paradigms in
one coherent framework. And successful interaction between the paradigms is
achieved through a common subset, WSML-Core.
7.7 Summary
In this chapter, we have presented the Web Service Modeling Language,
WSML, a language for the specification of various aspects of Semantic Web
services, based on WSMO. WSML brings together different logical-language
paradigms and unifies them into one syntactical framework, enabling the reuse
of proven reasoning techniques and tools. Unlike other proposals for the Se-
mantic Web and Semantic Web service languages, WSML has a normative
human-readable syntax that makes a separation between conceptual and log-
ical syntax, thereby enabling conceptual modeling according to a language-
independent metamodel (WSMO), while not restricting the expressiveness of
the language for the expert user. With the use of IRIs (the successor of URIs)
and the use of XML and RDF, WSML is a language based on the principles of
the Semantic Web and allows seamless integration with other Semantic Web
languages and applications.
The definition of an interoperability layer between the description logic and
rules paradigms (i.e. WSML-Core) enables the use and extension of the same
core ontology for a number of different reasoning tasks supported by a number
of different reasoners, most notably subsumption reasoning using description
logic reasoners and query answering using logic programming reasoners.
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