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Re: Action: #rdfms-identity-anon-resources questions

From: Graham Klyne <Graham.Klyne@Baltimore.com>
Date: Mon, 23 Jul 2001 21:37:33 +0100
Message-Id: <5.1.0.14.2.20010723212314.03c497b0@joy.songbird.com>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: RDF core WG <w3c-rdfcore-wg@w3.org>
At 07:40 AM 7/23/01 +0100, Brian McBride wrote:


>Graham Klyne wrote:
>
>[...]
> > 4. Can we agree whether or not unique generated IDs (in the style of Skolem
> > constants) are equivalent to existentially quantified variables for the
> > purpose of asserting the existence of a resource with properties
> > given?  (See Frank's message [10] for a discussion -- I discount the option
> > of dropping anonymous resources.)
>
>This is the key question.  I suggest we have established the following
>differences between a resource named by a URI and a resource identified
>by a quantified variable:
>
>   o scope:  An application given a resource identified by a URI
>     can reasonably expect to pass that URI to other applications and
>     that they should be able to recognise it - c.f. my example
>     on seeking references about a service offered in response to an ad.
>
>     If the response includes a reference to a service identified by
>     a URI, the receiver could reasonably pass that URI to reference
>     service to seek a credit/quality reference for that service.
>     There is no point doing that for a variable.

Agreed.

>   o binding: An application given a resource identified by a URI
>     can assume that URI denotes a specific resource - the
>     binding decision has been made - an existentially quantified
>     variable has not been bound to a specific resource.

I think the assumption that the URI denotes a specific resource is somewhat 
empty if one has no other knowledge about the resource thus denoted.  As 
Pat pointed out, in this situation you can do no more than infer that such 
a resource exists.

>   o provenance: when a source of rdf states some properties about
>     a resource named by a URI it is making assertions that the
>     resource named by that URI has those properties.  when a source
>     of rdf states properties about a variable, it is making no
>     assertions about the name of that resource.

The detailed form of the argument here depends a bit on whether one assumes 
that URIs:resources are 1:1, or if several URIs can identify the same 
resource.  But either way I assert that two URIs can ultimately refer to 
the same thing in the domain of interpretation.  Thus, assertions about a 
resource named by a uniquely-generated URI MAY be referring to a resource 
that is elsewhere known by a specified URI.  This seems to be the same as 
information that one has about a resource identified by a variable.

#g


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Graham Klyne                    Baltimore Technologies
Strategic Research              Content Security Group
<Graham.Klyne@Baltimore.com>    <http://www.mimesweeper.com>
                                 <http://www.baltimore.com>
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Received on Monday, 23 July 2001 18:05:41 EDT

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