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

Re: use/mention and reification

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Wed, 23 Jan 2002 13:46:17 +0200
To: ext Graham Klyne <Graham.Klyne@MIMEsweeper.com>
CC: Dan Brickley <danbri@w3.org>, Jan Grant <Jan.Grant@bristol.ac.uk>, Dan Connolly <connolly@w3.org>, RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B8746F29.C1E7%patrick.stickler@nokia.com>
On 2002-01-23 13:23, "ext Graham Klyne" <Graham.Klyne@MIMEsweeper.com>
wrote:


> How do we ever know who "Lois" or "Jimmy" really are?  (This is in danger
> of becoming philosophical which won't help this debate.)

As far as strings are concerned, we don't. As far as URIs in an RDF
context, we know insofar as those who use those URIs agree.

> I understood DanBri to be saying that he wasn't yet ready to assume that
> URIs have global scope:  that person:Lois in one context means the same as
> person:Lois in some completely different context.

Whether or not that is what Dan was saying, I find such a view to be
in total contradiction to the very purpose of using URIs as resource
identifiers in RDF in the first place. The whole point was to achieve
intersection of resources which reflects agreement of meaning.

If someone is not sure if their #Lois is the same as person:Lois, fine,
then don't use person:Lois to identify her. Leave it local, or use
some other namespace.

>  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
identity.

I.e., you weren't saying that <person:Lois> <ex:accepts> that
"Superman" <ex:is> <person:Superman>.
 
>> I agree with Jan's view that a URI ref denotes an RDF resource, and
>> whether two or more resources denote the same "thing" in some
>> universe is a separate issue. It is no different than whether or not
>> <dc:title> and <foo:title> mean the same thing or whether "5.0"
>> or "000005" or "5.000000" denote the same value.
>> 
>> Equality of things denoted by RDF resources in a given universe of
>> interpretation is a separate issue from identity and equality
>> of RDF resources in an RDF graph.
> 
> I have no argument with this...

Cool  ;-)

>> Reification using URI refs provides consistent identity of RDF
>> resources without forcing assertion, and quoting URI refs of
>> resources as literals is just going to add an unnecessary
>> layer of interpretation.
> 
> I'm slightly concerned that you may be muddling assertion of a statement
> with interpretation of resources.  As things stand, a URIref-labelled node
> in an RDF graph denotes some resource (per some interpretation)
> irrespective of whether or not any statement within which it appears is
> asserted.  

I thought that was what I said ;-)  I.e., I agree.

> Non-assertion of a statement doesn't somehow suspend
> interpretation of the graph nodes used to describe it.

I fully agree.

> Maybe this is what
> DanC and DanBri are arguing for?

Couldn't say.
 
> When I look at your example (below), I find myself worrying about what
> ex:#Superman actually denotes, and the extent to which that affects the
> truth of what you are expressing.  Absent some very special treatment of
> the reification vocabulary, there's nothing in the model theory (that I can
> see) that allows the various occurrences of "#Superman" to have different
> denotations (depending on whose belief is being described), which is what I
> think DanBri is trying to allow with his RDF-through-RDF scenario.

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. Maybe it means ex:Superman,
maybe not.

> 
>> Much better, I think, to say
>> 
>> --
>> 
>> <?xml version="1.0"?>
>> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>>          xmlns="ex:">
>> 
>> [snip]
>> 
>> </rdf:RDF>
>> 
>> --
>> 
>> Now we have the means to infer that there is some agreement
>> between the views of Lois and Jimmy, yet none of those views
>> are actually asserted, insofar as the expression of those
>> views are concerned -- and we also see that at least some
>> of their shared views intersect with asserted "real world
>> knowledge".
> 
> Yes (apart from possible the bit about "real world knowledge"), but that's
> not the issue that I'm chewing on.

I figured I'd get slapped on that one ;-)

Agreed, poor choice of terms. Let's just say "asserted knowledge" and
leave it at that.

>> The intersections between quoted and asserted knowledge from
>> the above example shows very nicely in the graph produced
>> by the W3C RDF validator.
>> 
>> Eh?
> 
> I don't know what you mean by "intersections between quoted and asserted
> knowledge".

The shared URI labeled nodes. I.e., the intersection of resources
shared by quoted/reified statements and asserted statements.

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 Wednesday, 23 January 2002 06:45:30 EST

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