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Re: Meaning of URIRefs

From: Sandro Hawke <sandro@w3.org>
Date: Fri, 25 Oct 2002 14:51:06 -0400
Message-Id: <200210251851.g9PIp6i25350@wadimousa.hawke.org>
To: Bob MacGregor <macgregor@ISI.EDU>
cc: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, www-rdf-interest@w3.org


> If I understand Sandro's position correctly, then if I use a URI
> foo:bar (when oh when are we going to finally add qnames to RDF?),
> I'm committed to "believing" all of the information
> stored in the corresponding document.

Right.   

I thought I'd addressed your two points in my reply to Peter; I'll try
again.

> Below, Sandro
> tempers that by saying you agree to all of the 'definitional'
> information.  There are at least two problems with Sandro's
> proposal.  One is that long experience with KR and DL systems
> indicates that a line between 'definitional' and 'non-definitional'
> is completely arbitrary, and therefore untenable as the basis
> of an RDF convention.  For example, I would hope that we
> would all agree(?) that an rdf:type statement is 'definitional' (how
> else do we define constants like PI?).  The statement
>       (foo:GeorgeBush rdf:type foo2:Person)
>   is perhaps non-controversial.  However the statement
>      (foo:GeorgeBush rdf:type foo2:SittingUSPresident)
> is not definitional.  A fanatical Gore supporter might claim that
> Al Gore is still the rightful US President.
> 
> Continuing, suppose the retort is that 'rdf:type' is NOT a definitional
> statement.  Then we have a disagreement over what should be
> definitional and what should not, which just backs up my claim above.

My proposed split-off of definitional information is NOT intended to
be done mechanically.  I tend to agree with your point that  dividing
"definitional" and "non-definitional" is, in the end, arbitrary.

I propose, rather, that the split be done by authors and publishers.
If you are "coining" a URIRef which you want others to use, you should
provide good definitional content, not contaminated by any other
information.  You should perhaps also make strong commitments to
steward that definition, but that's a different issue. 

> A second problem is that I might want to disagree with a statement
> by citing the URI, and Sandro's proposal appears to prevent that.
> If I want to state that the individual denoted by 'foo:GeorgeBush'
> is not the president, is not a Person, or whatever, I'm going to have
> to reference 'foo:GeorgeBush' in my refutation.
> 
> I imagine that Sandro might like to amend his proposal to allow
> quoted references to URI's without committing to their definitions?
> If we had quotation.  Otherwise, it would be hard to express (in RDF)
> a disagreement with how someone else had constructed their ontology.

I don't have to amend my proposal to allow this, since nothing I said
prevents it; you just have to keep such quoted URIs inside string
literals rather than use them as node or arc labels on your RDF graph.

But, again, there is a way to point to something without using a
quoted URI or a URI at all: you can refer to it by some collection of
properties which identify it unambiguously.  This is a technique often
used in RDF for identifying people.   It requires more difficult
reasoning, but if for some reason you can't obtain or create good
definitional content, it works.

    -- sandro
Received on Friday, 25 October 2002 14:51:48 GMT

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