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Pulling resources out of the graph (was Re: HTTP URIs for real world objects)

From: Danny Ayers <danny.ayers@gmail.com>
Date: Thu, 17 Jan 2008 10:49:11 +0100
Message-ID: <1f2ed5cd0801170149m8b43a15r5c0d5c0dfd614b4a@mail.gmail.com>
To: "Peter Ansell" <ansell.peter@gmail.com>
Cc: semantic-web@w3.org, "Jeremy Carroll" <jjc@hpl.hp.com>, peter@pensive.eu

[cc's tweaked]

On 17/01/2008, Peter Ansell <ansell.peter@gmail.com> wrote:

> > The subject of this thread is about URIs for real world "objects". RDF's fatal flaw in this respect is that it makes no distinction between use and mention of a subject (think Alice Through the Looking Glass and "the name of the song" - Lewis Carroll knew what he has talking about). I would still maintain that PSIds answer that requirement unequivocally, however poorly it might be considered that the documentation supports that view.
> I think any assertions with the ID/URI as the subject of a statement
> should be regarded as defining a property specifically about the thing
> that is being referred to.

Yes...I'm not sure I follow the use/mention point as it relates to RDF.

This could simply be my early-morning confusion. I was about to
suggest this issue does arise with RDF when used over HTTP for
documents (information resources), as when you do a GET on a Web
resource you always get a representation of that resource, not a
description of that resource (the issue discussed by Patrick Stickler
around URIQA [1]).

But I can't actually see the problem there right now... Seems to me a
description of something is a legitimate form of representation of it
- so if the publisher deems it appropriate, they can use the URI of
the resource as the subject of statements within the RDF
representation. i.e. no distinction is needed. Alternately, the
httpRange-14 trick of returning a 303 redirect could be used to
provide a description.

Incidentally, something I assume is closely related to the use/mention
point (whatever that may be :-) is something that's been bugging me
for a while. Say a HTTP GET on <uri> returns a doc containing the

<person> foaf:homepage <http://example.org/home> .

What can we say of the relationship between the resource <uri> and the
resources <person>, foaf:homepage and <http://example.org/home>?

Resources in RDF graphs are always linked nodes, but when HTTP is
brought into the picture it's as if there's an air gap between the
graph and the resources it involves. Can they somehow be reified?
(Generally, not as in RDF reification). Given the GET, would it be
reasonable to infer statements something like:

<uri> :involves <person> .
<uri> :involves foaf:homepage .
<uri> :involves <http://example.org/home> .

where :involves would probably be a subclass of rdfs:seeAlso
("involves" is an awful term but I'm not sure whether this is "uses"
or "mentions" :-)

This could be useful from a linked data perspective, in providing a
follow-your-nose path from e.g. <person> to <uri> (as links work both
ways) which might not otherwise exist even though <uri> provides
information about <person>.

But does it break anything?

(I was hoping the named graph docs might help here, but the HP links
from http://www.w3.org/2004/03/trix/ are 404ing)



Received on Thursday, 17 January 2008 09:49:23 UTC

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