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Anonymous Instances & Use of rdf:Resource as a class

From: Gary Ng <Gary.Ng@networkinference.com>
Date: Tue, 15 Jul 2003 17:20:11 +0100
Message-ID: <3BE4D3F0FB726240966DEF40418472B53E94FA@ni-lon-server1.ad.networkinference.com>
To: <public-webont-comments@w3.org>

Sorry if you have received it twice. This was posted in rdf-logic

Hi there,

I have two general questions regarding OWL ontologies. I couldn't find
the answers from the reference docs (it is probable that I have missed
it) but I have the following interpretation. So I was wondering how
other feels about them. Or better, what is the intended behaviour when a
tool encounters these things?

1. How should a parsing tool handle things that are declared to be

a. Either as instances, 
	<rdf:Resource rdf:ID="AResource"/>

b. or as the range of an ObjectProperty? 

	<owl:ObjectProperty rdf:ID="aProp">
		<rdfs:range rdf:resource="&rdf;Resource"/>

I interpret it as follows:

a. This should be allowed. Since rdf:Description is allowed, and
everything is an instance of rdf:Resource anyway. In this case AResource
should be treated as an instance of owl:Thing.

b. Strictly speaking, this should not be allowed. Since although
owl:Thing is a rdf:Resource, but not all rdf:Resources are owl:Thing,
and for a OWL-DL tool, this has gone out of the boundary and I would say
this falls into OWL-FULL.

2. Anonymous instances vs named instances. What is expected of them? 

Are all anonymous instances assumed unique? Given that in OWL there is
no unique name assumption, an anonymous instance could potentially be
identified with any other instances. For example, take the Measurement
in the reference doc. A reasoner could - by influence of other axioms -
infer that the Quantity individual is sameAs the Measurement individual,
except now there is no way for a client tool to determine what the
reasoner has done because there is no handles to the individuals. Have I
missed something?

Would appreciate any comments, or point me to previous mailings
regarding these issues.

Thanks very much,


p.s. Someone may have asked this before, apologies in advance. 
For example, in the wine/food ontology, there is no xml:base declared,
but the access URL (in owl:imports) contains the ".owl" extensions. 
As without xml:base, the access URL is taken as the namespace, thus
simply trying to import food.owl would lead to a mismatch in all names.
Are we suppose to just ignore the extensions? Or should xml:base really
be declared in those files? Or of course, change the access URL?

Gary Ng, PhD 	     gary.ng@networkinference.com
Senior Software Engineer
Network Inference (Holdings) Ltd
Tel: +44 (0) 20 7616 0717 Fax: +44 (0) 20 7616 0701
Received on Tuesday, 15 July 2003 12:20:18 UTC

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