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Resources and URIs

From: Tim Bray <tbray@textuality.com>
Date: Tue, 22 Apr 2003 13:03:53 -0700
Message-ID: <3EA5A029.8070601@textuality.com>
To: "Roy T. Fielding" <fielding@apache.org>
Cc: pat hayes <phayes@ai.uwf.edu>, John Cowan <cowan@mercury.ccil.org>, uri@w3c.org

Roy T. Fielding wrote:

> If you have suggested wording to change, then please suggest it.
> If you don't, then this is a redundant discussion and I have already
> answered it before:

I have a suggested wording change, because while I have been largely 
unimpressed by the philosophical jargon being thrown around here 
recently, I do agree that the current definition "A resource can be 
anything that has identity" offers significant room for improvement; 
among other things it deserves to be called out and not sequestered in a 
<dd>.

Here you go:

<h3>Resources and URIs</h3>

Many different abstract, informational, and physical things may be 
resources.  URIs exist to identify resources, but this "identity" 
relationship has both social and technical dimensions.

For example, it is incontrovertible that the URI 
http://www.tbray.org/A0.png identifies a resource which is a particular 
bitmapped graphic (I assert this, I control tbray.org, and the assertion 
is verifiable via technical means) and that the URI 
http://www.w3.org/1999/xhtml identifies a resource which is a well-known 
markup vocabulary (established by social convention).  It is possible 
for ambiguity to enter this relationship; for example, does 
http://www.w3.org/Consortium identify an organization or a particular 
HTML page on its website?

A few principles apply:
- While the definitions of URI and Resource are somewhat circular, the 
existence of a URI does not imply the existence of a resource.  For 
example, the URI http://example.com/386751531 identifies no resource.
- Formally, resources could exist without URIs - for example, there is a 
picture of my cat somewhere on http://www.tbray.org but I'm not 
publishing a URI.  However, such resources have no practical import or 
utility.
- URI schemes may impose constraints on the types of resource they 
identify; for example, ftp: URIs identify files and directories 
accessible using the FTP protocol.
- Ambiguity in the characterization of what resource a URI identifies is 
always undesirable and reduces the utility of both the resource and the URI.
Received on Tuesday, 22 April 2003 16:03:54 GMT

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