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RE: Subjects as Literals, [was Re: The Ordered List Ontology]

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 1 Jul 2010 02:53:31 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A001F07A6C@judith.fzi.de>
To: Jiří Procházka <ojirio@gmail.com>
Cc: "Linked Data community" <public-lod@w3.org>, "Semantic Web" <semantic-web@w3.org>
Jirí Procházka wrote:

>I wonder, when using owl:sameAs or related, to "name" literals to be
>able to say other useful thing about them in normal triples (datatype,
>language, etc) does it break OWL DL

Literals in owl:sameAs axioms are not allowed in OWL (1/2) DL. owl:sameAs
can only be used to equate individuals. An axiom of the form

    ex:u owl:sameAs "foo" .

would, however, equate an individual with a data value. The semantics of OWL
DL states that individuals and data values are disjoint [1], so such a
statement would always lead to semantic inconsistency. But, in fact, the
syntax of OWL DL disallows stating such an axiom, anyway: only URIs are
allowed in sameness axioms [2].

>(or any other formalism 

OWL Full allows it, both syntactically and semantically.

>which is base of some ontology extending RDF semantics)? 

OWL Full is an extension of the RDF Semantics in the sense of [3]. This
explains why OWL Full can treat sameAs'ed literals semantically without
problems: under the semantics of RDFS all data values are individuals
("rdfs:Literal rdfs:subClassOf rdfs:Resource"). So there is no disjointness
between data values and individuals as in OWL DL. Also, as for RDFS, OWL
Full allows for arbitrary RDF as input, so sameAs'ed literals are also
syntactically allowed.

Or would it if
>rdf:sameAs was introduced?

Such a definition would probably not be different from what OWL Full already
provides, only at a different semantic layer. So I would consider it
redundant in RDF.


[2] http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#Individual_Equality

[3] http://www.w3.org/TR/rdf-mt/#DefSemanticExtension

Dipl.-Inform. Michael Schneider
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Received on Thursday, 1 July 2010 00:54:08 UTC

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