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Re: RDF Graph questions

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Thu, 30 May 2002 10:11:34 +0300
To: Pat Hayes <phayes@ai.uwf.edu>, Brian McBride <bwm@hplb.hpl.hp.com>
CC: RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B91BAB56.15B31%patrick.stickler@nokia.com>

On 2002-05-29 21:32, "ext patrick hayes" <phayes@ai.uwf.edu> wrote:


>> We may choose to clarify those statements in M&S.
>> 
>> I propose the following test case.
>> 
>> Are the following two graphs, equal?
>> 
>>   <rdf:RDF xmlns:foo="http://example.org/b">
>>     <rdf:Description>
>>       <foo:ar>foobar</foo:ar>
>>     <rdf:Description>
>>   </rdf:RDF>
>> 
>> and
>> 
>>   <rdf:RDF xmlns:foo="http://example.org/ba">
>>     <rdf:Description>
>>       <foo:r>foobar</foo:r>
>>     <rdf:Description>
>>   </rdf:RDF>
>> 
>> Our present specs would say that they are.
>> 
>> My reading of M&S is that it says that these two fragments of
>> RDF/XML do not represent the same information as they 'associate'
>> the uri http://example.org/bar with different namespaces.
> 
> They do? Doesn't the xmlns:  just specify a prefix to be used in
> interpreting the foo: notation in the document? Surely there isn't
> any implication that http://example.org/ba  means anything at all by
> itself, is there (??)

Interestingly, both Brian and Pat are correct.

In the XML interpretation, we clearly have two different elements:

   qname:(http://example.org/b)ar
   qname:(http://example.org/ba)r

(c.f. http://ietf.org/internet-drafts/draft-pstickler-qname-01.txt)

which any XML processor would treat as distinctly different and which
could have radically different semantics and interpretation.

Yet, given the fact that RDF parsing throws away the boundary between
namespace and local name (as well as the context distinction between
element, element/attribute, and global/attribute), we end up with only
one URI in the RDF graph:

   "http://example.org/bar"

And hence, insofar as the RDF interpretation is concerned, the meaning
of the two distinct elements in the XML serializations are the same.

This was hashed out ad nauseum nearly a year ago on rdf-interest,
with myself as a major source of the noise, and the conclusion
was "tough, that's the way RDF works, it's up to the owner of
"http://example.org/" to make sure such crap doesn't happen".

If you have the stomach for it, c.f.

http://lists.w3.org/Archives/Public/www-rdf-interest/2001Aug/0061.html
http://lists.w3.org/Archives/Public/www-rdf-interest/2001Aug/0163.html

Patrick

--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Thursday, 30 May 2002 03:08:19 EDT

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