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ISSUE: Classes as instances

From: Raphael Volz <volz@aifb.uni-karlsruhe.de>
Date: Thu, 11 Jul 2002 17:04:06 +0200
To: "Webont" <www-webont-wg@w3.org>
Message-ID: <DMECLAFLIOFJEFFIAJPCIEIMCNAA.volz@aifb.uni-karlsruhe.de>

TITLE: Classes as instances
DESCRIPTION:
In certain cases it is necessary to represent "classes as instances"
<p>
<b>Scenario 1:</b>
Representing thesauri in OWL.
Thesauri are build on terms and have a set of predefined relations
to establish links between terms. One can distinguish two kinds
of approaches to represent thesauri for RDF(S):
<ol>
<li>Syntactic representation, such as done in
http://www.semanticweb.org/library/,
does not use classes to represent terms (or synsets in WordNet).
OWL could be
used to represent all terms as instances of a class <i>Term</i>.
Additionally
the set of relations can be tranlated to properties having this class as
domain
and range. Eventually additional features of these properties, such as
transitivity may
be specified, e.g. for the hyperonym relation.
<li>&quot;Semantic representation&quot;. Such as work carried out at the
university
of Karlsruhe. Here terms are converted to OWL classes and the hyperonym
relation is converted
to subclassof properties. All other thesaurus properties are difficult to
translate since
they are used to relate classes. However, in OWL properties do only relate
instances which are members of
the classes specified in domain and range constraints. The semantically
correct representation would
be to extend the metamodel of the ontology language, leading to information
that cannot be processed
by OWL aware agents. <p>
Another possibility is to treat classes as instances allowing to related
classes using properties
other than subclassof.
</ol>
<b>Scenario 2: Ontology Interoperability</b>
The representation of an entity as an instance or a class may depend on the
context and perspective of the user.
For example,  in a biological ontology, the class Orangutan may have
individual animals as its instances. However, the class Orangutan may itself
be an instance of the class Species. Note, that Orangutan is not a subclass
of Species, because then that would say that each instance of Orangutan (an
animal) is an instance of Species.
(example taken from R14 in http://www.w3.org/TR/webont-req/)
<p>
Since this decision may be context dependent, the issue of making classes
equivalent to instances arises in
ontology interoperability and mapping scenarios. For example, a boing 777
may be represented as an instance
of airplane in a general aviation ontology. However, in the ontology of a
particular aerospace company
boing 777 may be a class that has several instances. If both ontologies must
be aligned the appropriate mapping
must be able to bridge the distinct set of instances and classes.

RAISED BY: Raphael Volz, email of 7/11/02.
Received on Thursday, 11 July 2002 11:05:28 GMT

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