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RE: "Resource" (RDF vocabulary definitions)

From: Chris Catton <chris.catton@btopenworld.com>
Date: Mon, 25 Nov 2002 20:13:46 -0000
To: "Brian McBride" <bwm@hplb.hpl.hp.com>, "Dave Beckett" <dave.beckett@bristol.ac.uk>
Cc: "seth" <seth@robustai.net>, "www-rdf-comments" <www-rdf-comments@w3.org>
Message-ID: <OKEMLMGGGDAEEGEAKOBHCENLCEAA.chris.catton@btopenworld.com>

I may be losing the plot now, but I still think this is a circular argument.
Summarising what's gone so far ...

<http://example.org/somepage#MotorVehicle> from an rdf document refers to an
rdf resource.


So if I want to talk about the text on a web page I must define the URI:

   http://example.org/somepage#MotorVehicle

to mean the HTML fragment ...


But I can't do this, because when I try and define it, I automatically refer
to the resource and not the fragment

Brian McBride wrote>
>What you need is a URI that you know refers to the html representation of
>the resource.  I guess (YUK) we could define a urn or uri scheme for this:

Does this mean we agree there is a problem? - I'm genuinely not quite sure


> I think you are into an area that properly belongs in web
> architecture, not
> just RDF.  What exactly does a URI, or URL for that matter identify.  We
> architecture doesn't seem to be that well defined on this point,
> and it is
> all a bit tricky.

Well, it's certainly a problem for more than just rdf, but the semantic web
aint gonna work if we try to get a ticket to london on a text string or
print out a bus :-)
C

> -----Original Message-----
> From: Brian McBride [mailto:bwm@hplb.hpl.hp.com]
> Sent: 25 November 2002 14:33
> To: Chris Catton; Dave Beckett
> Cc: seth; www-rdf-comments
> Subject: RE: "Resource" (RDF vocabulary definitions)
>
>
> At 13:17 25/11/2002 +0000, Chris Catton wrote:
> >(This thread began in rdf interest)
> >
> >OK, my understanding is deepening I think, but I also think
> there is still
> >be a problem here.
>
> You may well be right.  Lets go through the logic of it and see.
> However,
> I think you are into an area that properly belongs in web
> architecture, not
> just RDF.  What exactly does a URI, or URL for that matter identify.  We
> architecture doesn't seem to be that well defined on this point,
> and it is
> all a bit tricky.
>
>
> >In my *rdf* document I write
> ><http://example.org/somepage#MotorVehicle>  rdf:type
> ><http://example.org#HtmlFragment>
> >
> >In my *html* document at http://example.org/somepage, i can
> write (stupidly
> >perhaps, but perfectly legally)
>
> It is not illegal to write stupid things, just unwise.  RDF has no
> pretensions to stop people writing things that are wrong or stupid.  I've
> no doubt one can construct cases that don't make sense, e.g.
>
>    <rdf:Description>
>      <rdf:type rdf:resource="&eg;sheep"/>
>      <rdf:type rdf:resource="&eg;tulip"/>
>      ...
>
>
> ><a name="MotorVehicle">model t ford type thing</a>
> >
> >and in the header on the same page (as suggested at
> >http://www.w3.org/RDF/FAQ#How )
> >
> ><rdf:Description rdf:ID="MotorVehicle">
> >   <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
> >   <rdfs:subClassOf
> >rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
> ></rdf:Description>
> >
> >Now:
> >1.      My html document is referred to from an rdf document and so
> >treated as an
> >rdf document. (stated in
http://www.w3.org/TR/rdf-concepts/#xtocid103660 )

Err, where exactly was your html *document* referred to from your rdf
document?  Do you mean:

   <http://example.org/somepage#MotorVehicle>  rdf:type ...

This does not refer to your html document.  It refers to the rdf resource
identified by:

    http://example.org/somepage#MotorVehicle

The HTML document is a *representation* of a resource, as best I can
understand the current state of web architecture.  There could be another
representation of that URI, e.g. in PDF format.



>2.      As an rdf document a reference to
>http://example.org/somepage#MotorVehicle refers to whatever the owner of
>http://example.org says it is - her car perhaps.
>3.      Her car is not an HtmlFragment - so we have a category error.
>
>So I don't see how I can reliably reference an html fragment from an rdf
>document.

Well, I guess you'd have to define the URI:

   http://example.org/somepage#MotorVehicle

to mean the HTML fragment, in contradiction to your statement above.

>Common sense might tell us what was meant, but I don't see the
>rules that let a machine decide.

An RDF processor never really 'knows' exactly what is meant by a URI.  It
doesn't have to.

>Anyone see a way out of this?

What you need is a URI that you know refers to the html representation of
the resource.  I guess (YUK) we could define a urn or uri scheme for this:

    rep:text/html:http://example.rog/somepage#MotorVehicle

which refers to a mime-type specific representation of URI.

>Paul
>Prescods post Re: a URI is a name (tel uri scheme and VCARD RDF) on
>rdf-interest suggests we don't need 2 URIs because we can use rdf to
>distinguish the meaning.  If we cannot actually reference the fragment
>reliably, this is not true.

I haven't read that - I better go look.

Brian
Received on Monday, 25 November 2002 15:19:22 GMT

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