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

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 23 Jul 2001 22:15:58 -0700
Message-Id: <v04210121b782b1cf0abd@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
>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.

I think this is wrong on several grounds. First, there is not in 
general any way to 'identify' the resource denoted by a URI. If I am 
given a URI then I may or may not be able to discover what resource 
it was intended to identify, but there is no general presumption that 
this can always be done. Second, while of course the other 
application can recognise the URI in the sense that they know where 
it comes from, there is no general presumption that they can 
'identify' what it denotes, ie discover exactly what resource that 
was supposed to be. In many cases this may be possible (eg it will be 
for URL's presumably), but not in general.

>    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.
>  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 disagree. What do you mean by 'binding' here? There doesnt seem to 
be any reasonable sense of binding for a URI. Certainly there isnt 
any way to bind a URI to the resource it denotes, in general (cf 
"A resource may also be an object that is not directly accessible via 
the Web; e.g. a  printed book. ..... Anything can have a URI; the 
extensibility of URIs allows the introduction of identifiers for any 
entity imaginable."

>  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.

In both cases, it is making assertions about some thing, ie some 
resource. The use of the URI may enable the receiver to connect the 
assertions made by the source to other assertions (perhaps made by 
other sources) about the same thing, made by using the same URI. That 
is the only sense in which a URI can be said to 'name' anything.

It isnt clear to me what the scope of anonymous node is intended to 
be, but it if it is the document containing the node, then indeed it 
should be impossible for any other source to say anything about the 
thing it refers to, so this is a genuine difference. However, the 
same is true of a non-anonymous URI if its use is restricted to this 
one source.



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Received on Tuesday, 24 July 2001 01:16:08 UTC

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