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Content-Location is your friend

From: Mark Baker <distobj@acm.org>
Date: Thu, 17 Jan 2002 12:28:11 -0500 (EST)
Message-Id: <200201171728.MAA15864@markbaker.ca>
To: patrick.stickler@nokia.com (Patrick Stickler)
Cc: urn-ietf@lists.netsol.com (URN), uri@w3.org (URI)

> The "use 'http:' URLs for everything' approach suggests
> that a given URL can be used both to denote the thing
> (the car) as well as be dereferenced to retrieve a
> representation of that thing (e.g. a photo, or technical
> specs, etc.) 


> Yet, a SW application which is trying to "understand"
> a given statement such as
>    <rdf:Description rdf:about="http://foo.com/freds_car/">
>       <dc:creator>Fred</dc:creator>
>    </rdf:Description>
> cannot tell whether Fred is the creator of the car itself
> or of the digital resource retrievable from the URL.

That's not true.  We've had this discussion before, and I've pointed
out that your assertion above is about the *resource*, i.e. the car.
If a particular representation of the car was created by somebody else,
then that should be reflected in a different URI, and the relationship
between http://foo.com/freds_car/ and this other URI should be
authoritatively established with HTTP's Content-Location header.


GET http://foo.com/freds_car/ HTTP/1.1
Host: foo.com
Accept: image/gif

response headers;

HTTP/1.1 200 OK
Content-Type: image/jpg
Content-Location: http://foo.com/freds_car/image?format=jpg

Then you could make assertions about that particular representation;

 <rdf:Description rdf:about="http://foo.com/freds_car/image?format=jpg">

Mark Baker, Chief Science Officer, Planetfred, Inc.
Ottawa, Ontario, CANADA.      mbaker@planetfred.com
http://www.markbaker.ca   http://www.planetfred.com
Received on Thursday, 17 January 2002 12:27:13 UTC

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