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RE: "Resource" (RDF vocabulary definitions)

From: Chris Catton <chris.catton@btopenworld.com>
Date: Sat, 23 Nov 2002 11:50:58 -0000
To: "David Menendez" <zednenem@psualum.com>, "RDF-Interest" <www-rdf-interest@w3.org>
Message-ID: <OKEMLMGGGDAEEGEAKOBHMEMDCEAA.chris.catton@btopenworld.com>

I'm also more than a bit mystified by
http://www.w3.org/TR/rdf-concepts/#xtocid103660

As I read it, if in my rdf graph I use a fragment http://example.org/#foo
this points at a foo as defined in the rdf document at http://example.org.
It is not an option that http://example.org is not an rdf document.
(the relevant section is 'So when someurl#frag is used in an RDF document,
someurl is presumed to designate an RDF document. )

I interpret this as having two consequences:
First, I cannot say something in rdf about a fragment in an html document -
because it is presumed to be an rdf document.
Second, I cannot say anything in rdf about a definition in rdf (such as 'the
comment about the class defined at http://example.org/#foo contains an
error').

The second consequence may be a pragmatic one.  The first seems very odd and
probably not what was intended, as suggested by the line ...
'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'
which sort of suggests that it might also be possible to indicate a thing
that is internal to the document - though it's not at all clear how.

I'd previously assumed that if a fragment pointed at something inside an rdf
tag then it pointed to the foo as defined in rdf.  If it pointed to
something inside an html tag, then it pointed at the text (or image or
whatever).
So http://example.org/#unicorn pointed at the concept of a unicorn if the
target of the fragment is inside rdf tags, but at the text that lay within
the anchor tags if inside an html document.

The thread on contexts seems to be floundering around with the same issues,
and it seems to me we need a much clearer statement of what a URI is
actually referencing.  Or am I missing something?

Chris

-----Original Message-----
From: www-rdf-interest-request@w3.org
[mailto:www-rdf-interest-request@w3.org]On Behalf Of David Menendez
Sent: 23 November 2002 05:54
To: RDF-Interest
Subject: RE: "Resource" (RDF vocabulary definitions)



At 11:12 AM +0000 2002-11-22, Jon Hanna wrote:
>  > What about URI references which include fragment identifiers? My
>>  reading of RFC 2396 is that <http://example.org/> and
>>  <http://example.org/#foo> refer to the same resource.
>
>In the case of http://example.org/#foo the URI (http://example.org/) is a
>URI identifying a resource. The fragment identifier (#foo) is either:
>
>a. meaningless.
>b. An identifier of a resource that is part of the resource identified by
>the URI.
<snip>
>any system that uses URIRefs in an opaque manner (such as RDF) must
>assume that a URIRef with a fragment identifier refers to a
>different resource to the same URIRef without the fragment

Sounds good to me. I must have missed the part of RFC 2396 which
discusses resources that are part of other resources.

I guess some of my confusion/concern about fragment identifiers in
RDF is coming from the discussion in RDF Concepts [1], particularly
the part where it states:

>we assume that the URI part (i.e. excluding fragment identifier)
>indicates a Web resource with an RDF representation. So when
>someurl#frag is used in an RDF document, someurl is presumed to
>designate an RDF document.

If I have a some fragment of an HTML document, like a weblog posting,
and it has a URI reference like <http://example.org/00231#b>, and I
want to say something like
   <http://example.org/00231#b> dc:creator "Joe Example".
is that precluded by the presumption that <http://example.org/00231>
is an RDF document instead of, say, an HTML document? I'm not sure
how to interpret what that section says.

[1] http://www.w3.org/TR/rdf-concepts/#xtocid103660
--
Dave Menendez - zednenem@psualum.com - http://www.eyrie.org/~zednenem/
Received on Saturday, 23 November 2002 07:45:13 GMT

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