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schema vs ontology

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Mon, 29 Apr 2002 11:02:43 +0100
Message-Id: <>
To: Dan Brickley <danbri@w3.org>
Cc: <w3c-rdfcore-wg@w3.org>
At 06:20 AM 4/26/02 -0400, Dan Brickley wrote:
>Another worry re terminology is that we have two Semantic Web working
>groups. One group calls RDF schemas 'schemas', the other calls them
>'ontologies'. To date we've not really used the latter term in RDF Core
>specs. I personally don't like it, but that's not important. What is
>importnat is terminological consistency at least within the RDF-based
>corner of W3C's work. I'm stumped as to what we do about that. People will
>ask us (of some RDF/XML schema that uses WebOnt machinery) whether it is
>an 'ontology' or a 'schema'. Maybe we don't need an answer, but it does
>seem a bit odd to not know collectively (in WebOnt + RDF Core) what we
>think we're talking about. Editorial suggestions / contribs on this

Hmmm... I think we ought to be wary about conflating schemas and 
ontologies.  They are, I think, related but different ideas.  Let's see if 
I can say why...

According to John Sowa ["Knowledge Representation", appendix B], an 
ontology is:
a catalogue of the types of things that are assumed to exist in a domain of 
interest [[D]] from the perspective of a person who uses a language [[L]] 
for talking about [[D]].

By contrast, I'd say that a schema is a catalogue of terms in some 
language, together with descriptions of how they can or should be used.

The first difference that appears to me is that
- an ontology is focused on the domain of discourse (semantics), even if 
with reference to a particular language, where
- a schema is focused on the language (syntax).

Further, it seems to me that a schema describes a vocabulary, only some 
terms of which may relate to ontological categories.

In summary, I think we should restrict our discussions to the term 
"schema", as used to describe the vocabulary of RDF.  Other groups may have 
a proper desire or need to use the term "ontology" to talk or reason about 
categories in their domain of discourse, using RDF language and schema as a 
vehicle for expressing some of those ideas.



John Sowa's Knowledge Representation Appendix B goes on to discuss 
languages like CGs and KIF as ontologically neutral, and then to discuss 
informal and formal ontologies, and in particular axiomatized ontologies.

Against that background, I think that RDF schemas are language tools that 
is/will be used and augmented by DAML/OWL to describe axiomatized ontologies.

I think that the when a schema is described as an ontology, it would be 
more correct to call it a description of an ontology.  This seems to be one 
of those conveniences of expression that is all very well as long as the 
underlying distinctions are understood.

Graham Klyne
Received on Monday, 29 April 2002 07:00:28 UTC

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