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RE: RDFTM Disposition of Comments (RDFTM-DC001)

From: Peter Patel-Schneider <pfps@comcast.net>
Date: Thu, 24 Mar 2005 07:14:14 -0500
Message-ID: <4242AF16.6050903@comcast.net>
To: public-swbp-wg@w3.org

> From: Steve Pepper <pepper@ontopia.net 
> <mailto:pepper@ontopia.net?Subject=RE:%20RDFTM%20Disposition%20of%20Comments%20%28RDFTM-DC001%29&In-Reply-To=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E&References=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E>> 
> Date: Thu, 24 Mar 2005 11:17:55 +0100
> To: "Dan Connolly" <connolly@w3.org 
> <mailto:connolly@w3.org?Subject=RE:%20RDFTM%20Disposition%20of%20Comments%20%28RDFTM-DC001%29&In-Reply-To=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E&References=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E>> 
> Cc: "SWBPD list" <public-swbp-wg@w3.org 
> <mailto:public-swbp-wg@w3.org?Subject=RE:%20RDFTM%20Disposition%20of%20Comments%20%28RDFTM-DC001%29&In-Reply-To=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E&References=%3CFOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net%3E>> 
> Message-ID: <FOEHKIENIPCJNPNFKGJNGEFMGJAB.pepper@ontopia.net>
>* Steve Pepper
>| We are talking about the *base* RDF model in which a resource can
>| only have a single URI as an identifier.
>* Dan Connolly
>| Er... no, that's just not the case. A resource can have any
>| number of URIs as identifiers.
>I don't think we disagree (I hope :) but there is clearly an
>issue of terminology that needs to be sorted out here.
>I may have this completely wrong and, if so, correct me, but
>my understanding is as follows:
>1) Resources in RDF are represented by nodes
>2) A node may have at most one URI reference (some have none)
>3) The URI reference of a node is an identifier for the resource
>   represented by the node
>4) In the absence of a vocabulary beyond that defined by RDF
>   itself, a resource can thus only have a single identifier.
>Clearly an RDF graph may contain multiple nodes (with different
>URIrefs) that are *intended* to represent the same resource, but
>in the absence of a property such as owl:sameAs, there is no way
>for an application to know that they do in fact represent the
>same resource.
>Am I right so far?
No, I don't think so, and this goes to the heart of some of my other 
comments about the interoperability survey.  The meaning of RDF is 
defined by the RDF semantics, not the syntactic details of RDF graphs.

A resource in RDF is a member of the domain of discourse.  Nodes in RDF 
graphs map to resources.  It is true that nodes have at most one URI 
reference associated with them, but the mapping from nodes to resources 
is many to one, so resources in RDF can have multiple URIs "associated" 
with them.  It is also true that RDF has very few capabilities (maybe 
none?) for forcing two nodes to map to the same resource, so it is 
difficult (impossible?) in RDF to force a resource to have more than one 
URI associated with it.

Peter F. Patel-Schneider
Bell Labs Research
Received on Thursday, 24 March 2005 12:11:24 UTC

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