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RE: Possible new issue: Things with and without identity?

From: Julian Reschke <julian.reschke@greenbytes.de>
Date: Thu, 12 Sep 2002 20:30:51 +0200
To: "Roy T. Fielding" <fielding@apache.org>
Cc: <uri@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCGEHGFFAA.julian.reschke@greenbytes.de>

> From: uri-request@w3.org [mailto:uri-request@w3.org]On Behalf Of Roy T.
> Fielding
> Sent: Tuesday, September 10, 2002 6:49 PM
> To: Julian Reschke
> Cc: uri@w3.org
> Subject: Re: Possible new issue: Things with and without identity?
>
> ..
>
> >> WebDAV talks about it that way because, for the purpose of authoring,
> >> it doesn't matter whether there is a distinction between the resource
> >> and the current representation of that resource -- they become
> >> effectively
> >> the same thing because WebDAV actions exist at an instant in time and
> >> only work on resources that are directly authorable (one-to-one
> >> relationship between representation and resource).
> >
> > That's news to me. Are you saying that WebDAV resources may not vary
> > depending on the headers in a GET request?
>
> A "WebDAV resource" is just an HTTP resource.  Any resource that allows
> PUT cannot vary depending on the headers of a GET request, since
> any such variance would be eliminated by the PUT.  However, other

That would basically mean that for every URI to which I can apply PUT,
there's only one representation a subsequent GET will deliver, so it doesn't
vary. It's certainly possible to use PUT this way, but I'm wondering where
the HTTP spec makes this a requirement? Looking at section 9.6, it seems
also plausible to consider GET and PUT to be symmetric. So I'd be allowed to
PUT to different representations of a resource with, let's say, varying
"content-language" headers. If you say that this is illegal, I'd like to
understand where RFC2616 forbids that.

Is there possibly another RFC that would say more about authoring HTTP
resources that can vary?

> resources that are derived from that resource may also be impacted by
> that PUT, and those other resources may vary depending on headers.
> That is the nature of content negotiation in HTTP -- the negotiable
> URI is never the same as the source URI.

Q: you're using the term "source URI" as if it was formally defined
somewhere... If I understand you correctly, the source URI upon a GET that
varies would be the URI returned in the "Content-Location" header, right? As
far as I understand section 14.14, a server MAY report this URI, but it
doesn't have to. So, is your point that for an authorable resource, there
should *always* be a source URI for each individual entity that can be
modified?

Julian

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Received on Thursday, 12 September 2002 14:31:24 UTC

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