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Description of rdfs:isDefinedBy in RDF Schema WD

From: Pete Johnston <p.johnston@ukoln.ac.uk>
Date: Fri, 22 Nov 2002 12:50:52 -0000
To: www-rdf-comments@w3.org
Message-ID: <000201c29225$ca8a1f10$2392268a@ulpcpj>

Hi,

This is really a request for clarification on the descriptions of the
rdfs:isDefinedBy property in

http://www.w3.org/TR/rdf-schema/

I notice that in the table of "RDF Properties" in the RDF Schema
Overview section (and in the rdfs:comment in the schema in Appendix B),
the description of rdfs:isDefinedBy is:

> Indicates the namespace of a resource

and further down under RDF Utility Classes and Properties:

> The property rdfs:isDefinedBy is a subproperty of rdfs:seeAlso, and
> indicates the resource defining the subject resource.

A while back I asked a question on dc-architecture about the usage of
rdfs:isDefinedBy, and specifically whether rdfs:isDefinedBy could/should
be used to express the relationship between a term and a namespace  

http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0205&L=dc-architecture&T=
0&F=&S=&P=1996

The question spawned a very long debate which I seem to recall spread
across several mailing lists, with opposed views presented, particularly
at

http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0206&L=dc-architecture&T=
0&F=&S=&P=805 [Dan Brickley]

which includes

----
rdfs:isDefinedBy probably should have been called rdfs:ns, since we
added it to RDF Schema as a way of associating a term with the wider
bundle of names it was defined alongside.
----

and

http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0206&L=dc-architecture&T=
0&F=&S=&P=1473 [Patrick Stickler]

which concludes

----
So the bottom line is that, if you want a property to relate a term to a
specific namespace then you need something other than rdfs:isDefinedBy.
And ideally, you would also instruct every parser to always assert such
statements for every term when parsing. But no existing RDF mechanism
provides for unambiguous preservation of namespace structure.
----

I tried to follow the ensuing debate as it surfaced in the archive of
the RDF Core WG list, and I think the latest references were in the
thread following

http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jun/0027.html
[Dan Brickley]

This message includes the suggestion

----
For every RDF property there is exactly one correct value for the
rdfs:isDefinedBy property.

When RDF graphs are written in the RDF/XML 1.0 syntax, this value
corresponds to the XML namespace URIref used in the serialized
representation of the RDF properties.
----

While I must admit this approach rather appealed to me (and I think that
convention is used, for example, in the RDFS representations of the DCMI
vocabularies), I also understand the argument that namespaces do not
exist in RDF and I thought that later contributions on that thread e.g.

http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jun/0031.html

http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jun/0147.html

reflected opposition to this very "tight" description of
rdfs:isDefinedBy, and it was considered inappropriate to limit
rdfs:isDefinedBy in this way. 

This would seem to be reflected in this message

http://lists.w3.org/Archives/Public/www-rdf-comments/2002JulSep/0095.htm
l

on the resolution of the issue.

But the text in the recent draft (especially the phrase "Indicates the
namespace of a resource") seems to re-introduce some ambiguity on
whether 

(a) the value of rdfs:isDefinedBy is (in all cases?) the XML namespace
URIref used to represent a property in the XML serialization, or 

(b) it is a reference to _any_ resource providing more information
(which _may_ be an XML namespace URIref, which _may_ point to a schema
(an RDF/XML document), but might not be).
 
Regards,
Pete Johnston

------- 
Pete Johnston 
Interoperability Research Officer 
UKOLN, University of Bath, Bath BA2 7AY, UK 
tel: +44 (0)1225 383619    fax: +44 (0)1225 386838 
mailto:p.johnston@ukoln.ac.uk 
http://www.ukoln.ac.uk/ukoln/staff/p.johnston/
 
Received on Friday, 22 November 2002 08:06:22 GMT

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