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Re: Meaning of URIRefs

From: Bob MacGregor <macgregor@ISI.EDU>
Date: Fri, 25 Oct 2002 08:57:23 -0700
Cc: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, www-rdf-interest@w3.org
To: Sandro Hawke <sandro@w3.org>
Message-Id: <7320DC18-E832-11D6-B09A-000A27DC4AB0@isi.edu>

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.  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.

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.

- Bob

On Friday, October 25, 2002, at 08:10 AM, Sandro Hawke wrote:

> In a message sent to www-rdf-comments that was intented for this list,
> Peter F. Patel-Schneider wrote:
>> [A discussion on whether using foo#bar commits one to the information
>> available at foo, moved from www-rdf-comments.]
>> Sandro's position is that the use of a URI reference commits one to the
>> entirety of the information in the document that can be found by
>> dereferencing the non-fragment part of the URI reference.
>> The basic problem that I have with this position is that I feel that it
>> poses a significant bar to communication.
>> To pick a very mundane example, suppose that company A has a URI,
>> http://A.com.ex/invoice.rdf, whose contents consist of invoices.
>> The first problem with Sandro's position is that company A has a 
>> serious
>> dilemma in placing identifiers for other companies in these invoices.  
>> The
>> only reasonable kind of identifier for another company, say company B,
>> would be a URI reference from a URI controlled by company B.  But the
>> simple use of this URI reference, say http://B.com.ex#B, commits 
>> company A
>> to everything said on http://B.com.ex.  It is certain that 
>> http://B.com.ex
>> is going to make disputable claims about company B, which company A 
>> does
>> not want to commit to.
>> The second problem with Sandro's position is that other companies are 
>> going
>> to have problems in disputing the invoices of company A.  The only way 
>> they
>> have to refer to these invoices is via URI references taken from
>> http://A.com.ex/invoice.rdf, but just the use of one of these URI
>> references commits the other company to the information in
>> http://A.com.ex/invoice.rdf, which is going to include the fact that 
>> the
>> invoice in question is a valid invoice.
>> I don't see any way around these dilemmas without denying Sandro's
>> position.
> The way around these problems is to split definitional content and
> general content into different documents.  The definitional content
> about the invoice would include information like the invoice number
> and an identifier for the parties issuing the invoice.  The general
> content about the invoice would include identifying the goods and
> services rendered, their prices, etc.  A dispute over the definitional
> content would have quite a different quality than a dispute over the
> general content; it would probably be resolved by finding the right
> invoice.
> Similarly, the definitional information about company B should only
> make claims which serve to identify company B, such as its official
> (name, jurisdiction) pair.  Additional information (such as its
> dispute resolution policies) belong elsewhere.
> If companies A and B choose not to offer such unencumbered
> definitional content, then others are free to do so.  In the worst
> case, where no one is willing to publish such a definition, one can
> always fall back to doing it with a bNode inside your own document.
> This fallback approach requires reasoning about inverse functional
> properties instead of just string-equality, but it is already in use
> [1] [2].
> In situations where the definitions are more complex, and many terms
> are interrelated (such as with OWL, DC, CC, RSS, ... basically any
> non-trivial ontology) this bNode approach is less feasible.  Then it
> becomes more important to have a stable URI for good definitional
> content, but it's also much more likely because the ontology creators
> are likely to understand this issue better.
>     -- sandro
> [1] http://www-106.ibm.com/developerworks/xml/library/x-foaf2.html
> [2] http://lists.w3.org/Archives/Public/www-rdf-logic/2001Sep/0004.html
Received on Friday, 25 October 2002 11:56:49 UTC

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