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Re: Qualities of URLs and resources

From: Roy T. Fielding <fielding@kiwi.ICS.UCI.EDU>
Date: Fri, 25 Feb 2000 16:09:55 -0800
To: Jim Davis <jrd3@alum.mit.edu>
cc: w3c-dist-auth@w3.org
Message-ID: <200002251609.aa12298@gremlin-relay.ics.uci.edu>
>Hmm, do you mean referenceable by humans in daily discourse, or
>referenceable via the HTTP protocol?  

I mean anything that can be represented.  Mostly nouns (is a color
a noun or an adjective, or both -- I can't remember, but I do know
it can be represented as a resource).

>Humans are able to talk about many things, including "the current President
>of the United States", "the first human to walk on Mars", and "unicorns",
>but none of these "references" are references that HTTP could use.  I don't
>think any of them count as URLs, and thus none of those referenda are
>resources, in the technical sense of HTTP.

What makes you think that those can't be identified as URLs and used
by HTTP?  Keep in mind that HTTP is a gateway protocol that is
capable of infinite redirections.

If I define


to mean the current President of the United States, then I can define
an HTTP service that accepts requests for that namespace and responds
with a representation of the current President.


   1) HTTP transfers representations, not resources;

   2) The resource defines the semantic mapping between requests
      and representations;

   3) The implementation of this mapping has nothing whatsoever
      to do with the semantics of the resource UNLESS the specific
      URI in question identifies an implementation itself as a resource;

   4) Many resources can only be manipulated by a subset of HTTP methods.

Received on Friday, 25 February 2000 19:10:00 UTC

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