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Re: RDF Concepts and Data Model document

From: Tim Berners-Lee <timbl@w3.org>
Date: Tue, 17 Sep 2002 22:51:18 -0400
Cc: www-tag@w3.org
To: "Williams, Stuart" <skw@hplb.hpl.hp.com>
Message-Id: <814A1EC6-CAB1-11D6-A525-000393914268@w3.org>
Indeed, Section 4.2 was what I was thinking of,
< http://www.w3.org/TR/rdf-concepts/#xtocid103660 > .

Tim

_________

"""4.2 Fragment identifiers

How should RDF treat a URI reference with a fragment identifier? 
Conventional web architecture has that the meaning of a fragment 
identifier is dependent on the MIME type of a resource that is obtained 
by dereferencing the URI part. URIs without fragment identifiers are 
generally presumed to map to some resource for which a Web 
representation (or several) can be retrieved. But RDF has no concept of 
a fragment identifier separate from a URI: RDF treats a URI reference as 
an opaque identifier that denotes some resource [RDF-SEMANTICS]. 
Further, an RDF resource identifier may denote something that is not 
web-retrievable; e.g. a car, or a Unicorn.

These apparently conflicting interpretations can be reconciled if:

*	we assume that the URI part (i.e. excluding fragment identifier) of 
any URI reference used in an RDF document indicates a Web resource with 
an RDF representation. (If it is not dereferencable as such on the web, 
so be it, but we must assume its notional existence.) So when 
someurl#frag is used in an RDF document, someurl is presumed to 
designate an RDF document.
*	when used in an rdf document, someurl#frag means the thing that is 
indicated, according to the rules of the application/rdf+xml mime type 
as a "fragment" or "view" of the RDF document at someurl. If the 
document doesn't exist, or can't be retrieved, then exactly what that 
view may be is somewhat undetermined, but that doesn't stop us from 
using RDF to say things about it.
*	the RDF interpretation of a fragment identifier allows it to 
indicate a thing that is entirely external to the document, or even to 
the "shared information space" known as the Web. That is, it can be an 
abstract idea, like my car or a mythical Unicorn.
*	thus, an RDF document acts as an intermediary between some web 
retrievable documents (itself, at least, also any other web-retrievable 
URIs that it may use, including schema URIs and references to other RDF 
documents), and some set of abstract or non-Web entities that the RDF 
may describe.


This provides a handling of URI referencess and their denotation that is 
consistent with the RDF model theory and usage, and also with 
conventional web axioms. This approach somewhat extends the idea of a 
"fragment" or "view" beyond the common idea (when handling web 
documents) that it is a physical part of a containing document.

In view of this, it is reasonable to consider that URIs without fragment 
identifiers are most helpfully used for indicating web-retrievable 
resources (when used in RDF), and URIs with fragment identifiers are 
used for abstract ideas that don't have a direct web representation. 
This is not a hard-and-fast distinction, as the line between resources 
having or not having a web-retrievable representation is sometimes hard 
to draw precisely."""



On Monday, September 16, 2002, at 04:35 PM, Williams, Stuart wrote:

> Tim,
>
> I think this is probably the RDF publication that you had in mind.
>
> http://www.w3.org/TR/rdf-concepts/
>
Received on Wednesday, 18 September 2002 08:18:23 GMT

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