W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > January 2002

Re: use/mention and reification

From: Frank Manola <fmanola@mitre.org>
Date: Wed, 23 Jan 2002 10:42:01 -0500
Message-ID: <3C4ED9C9.3030607@mitre.org>
To: Patrick Stickler <patrick.stickler@nokia.com>
CC: ext Graham Klyne <Graham.Klyne@mimesweeper.com>, RDF Core <w3c-rdfcore-wg@w3.org>
I wonder if you guys could clarify something for me about this 
discussion?  In the interchange below, Graham says:

 >>I think some alternative formulation of this scenario could lead to a
 >>situation in which Clark Kent and Superman have universally accepted
 >>denotations, and URIs may then be appropriate.

And in an earier interchange, Patrick said:

"I wouldn't expect any URI labeled resource to have different 
denotations.  If one says ex:Superman, one means ex:Superman.  If one 
says "Superman" then there is no way to know what is meant."

I certainly agree that "If one says "Superman" then there is no way to 
know what is meant" [ignoring a lot of descriptive information that may 
be provided about "Superman", which is irrelevant here].  However, it 
seems to me that both the bits I've quoted ascribe a lot more precision 
to URIs than is realistically going to be possible, at least about 
non-data things like people named by URIs.  It seems to me you guys are 
saying that the use of URIs is inappropriate unless there's universal 
agreement on what the URIs denote.  Am I wrong?  If I'm right, exactly 
what does that mean?

It seems to me that the situation is:

1.  If two people use the same non-URI, like "Superman", to refer to 
something, we don't know whether they mean the same thing or not, at 
least not by the use of the string "Superman" alone.  We may infer that 
they are talking about the same thing (with greater or less probability) 
on the basis of additional descriptive information they provide about 
the things they are talking about.

2.  If two people use different non-URIs, like "Superman" and "Clark 
Kent", to refer to (apparently) different things, the same thing holds. 
  We know they've used different names, but we may still infer they are 
talking about the same thing if we get enough additional information.

3.  If two people use the same URI, like ex:Superman, to refer to 
something, we know that they *think* they are talking about the same 
thing, but they may not be.  E.g.,

a.  One person may have introduced the URI ex:Superman, and someone else 
starts using it, but the second person actually has something else in mind.

b.  The two people involved have the same entity in mind, but have 
different understandings about that entity's attributes.  Consider 
ex:Clark Kent.  One person thinks Clark is identical to Superman, and 
the other (Lois) doesn't.  One person thinks Clark has Xray vision (and 
conceals it), the other thinks Clark has ordinary vision.

I don't see how we can reasonably expect URIs to be used only in 
situations where everyone on the Web has a full understanding and 
agreement on all the attributes of the thing the URI names before they 
start using it.  What we do get using URIs is the extra bit of 
information suggested by #3 above:  that when people use the same URI, 
they at least *think* they are talking about the same thing.  That's 
useful information!  You can merge their different beliefs via the URI 
in their various RDF graphs, and then possibly detect inconsistencies, 
which could then lead to better agreement after some dialog.

Another way of putting this is to ask if not allowing URI labeled 
resources to have different denotations means that different people 
can't attribute contradictory things to the same URI labeled resource?


Patrick Stickler wrote:

> On 2002-01-23 14:10, "ext Graham Klyne" <Graham.Klyne@MIMEsweeper.com>
> wrote:
>>At 01:46 PM 1/23/02 +0200, Patrick Stickler wrote:
>>>> OTOH, without allowing
>>>>that it seems that URI-refs don't offer anything that label strings like
>>>>"Lois" and "Jimmy" don't also offer.  The point of my comment was to
>>>>suggest that matters relating to personal belief of identity shouldn't
>>>>really be expressed in terms of URIs.
>>>But your examples are not about belief of identity, they
>>>are about belief of properties of entities which are given
>>>I.e., you weren't saying that <person:Lois> <ex:accepts> that
>>>"Superman" <ex:is> <person:Superman>.
>>My take on this scenario was that Lois' non-belief that Clark Kent is
>>strong is rather bound up with her belief about the identity of the person
>>she knows as "Clark Kent";  i.e. that she does not recognize him as also
>>being the person she knows as "Superman".
>>I think some alternative formulation of this scenario could lead to a
>>situation in which Clark Kent and Superman have universally accepted
>>denotations, and URIs may then be appropriate.  In this case, I think that
>>it's not possible that they denote exactly the same thing;  e.g. Clark Kent
>>denotes a person X wearing a suit and glasses;  Superman denotes the same
>>person X wearing a natty blue-and-red number.  In this formulation, using
>>URIs seems less troublesome.
> I see your point. Though I'm not sure that the Dan's do. Talking about
> some person X named "Superman" (who might later be deemed to equate to
> <person:Superman>) is not the same as using "person:Superman" rather
> than <person:Superman> to avoid instantiating a URI labeled resource
> node in the RDF graph.
> Eh?
> Patrick
> --
> Patrick Stickler              Phone: +358 50 483 9453
> Senior Research Scientist     Fax:   +358 7180 35409
> Nokia Research Center         Email: patrick.stickler@nokia.com

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Wednesday, 23 January 2002 10:34:37 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 7 January 2015 14:53:54 UTC