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RE: Label header vs PROPFIND depth 1

From: Julian Reschke <julian.reschke@greenbytes.de>
Date: Wed, 24 Apr 2002 16:34:59 +0200
To: <tim@ellison.name>, "'Deltav WG'" <ietf-dav-versioning@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCCEIMEHAA.julian.reschke@greenbytes.de>
Tim,

great.

My position is that if you don't consider the version selected by the LABEL
header to be a variant (representation) of the VCR, then it MUST NOT be
returned by a GET on the VCR URI.

RFC2616, section 1.3:

variant

A resource may have one, or more than one, representation(s) associated with
it at any given instant. Each of these representations is termed a
`varriant'. Use of the term `variant' does not necessarily imply that the
resource is subject to content negotiation.



> -----Original Message-----
> From: ietf-dav-versioning-request@w3.org
> [mailto:ietf-dav-versioning-request@w3.org]On Behalf Of Tim Ellison
> Sent: Tuesday, April 23, 2002 12:16 PM
> To: 'Deltav WG'
> Subject: RE: Label header vs PROPFIND depth 1
>
>
> I agree that there is no point in getting into the details unless we agree
> whether a version is a variant of a checked-in version-controlled
> resource.
> Once we get agreement on that we can go through the remainder of
> the issues
> and use that as a guidepost.
>
> So, you think it is a variant, and I think it isn't.
>
> Anybody else like to chip-in?  (anybody else following this or
> has everyone
> else gone home<g>?)
>
> Regards,
> Tim
>
> > -----Original Message-----
> > From: Julian Reschke [mailto:julian.reschke@greenbytes.de]
> > Sent: 23 April 2002 10:42
> > To: tim@ellison.name; 'Deltav WG'
> > Subject: RE: Label header vs PROPFIND depth 1
> >
> >
> > Tim,
> >
> > before going into details, I'd like to repeat that the way the
> > label header
> > is defined makes the selected revision a variant of the VCR. That's what
> > RFC2616 says, and IMHO there's no way to avoid that.
> >
> > If you strongly feel that this is a problem (I may agree), than
> the label
> > header should be removed from the spec (deprecated in the issues
> > list), and
> > we should go back looking at the original requirements it's supposed to
> > handle.
> >
> > > From: ietf-dav-versioning-request@w3.org
> > > [mailto:ietf-dav-versioning-request@w3.org]On Behalf Of Tim Ellison
> > > Sent: Tuesday, April 23, 2002 10:58 AM
> > > To: 'Deltav WG'
> > > Subject: RE: Label header vs PROPFIND depth 1
> > >
> > >
> > > Juliam wrote:
> > >
> > > > > Right, so imagine what kind of answer you would get back in the
> > > > > multistatus -- some would be from the unversioned resource
> > > propfinds and
> > > > > some from version propfinds, and you wouldn't know which were
> > > versioned
> > > > > (without explictly looking for a live property to distinguishe
> > > > > them), _and_
> > > >
> > > > Yes -- I think this is what RFC3253 says.
> > > >
> > > > > it would contravene the 2518 depth result requirement I
> > > > mentioned earlier.
> > > >
> > > > I don't think so.
> > >
> > > From your example below I see that you envisage the hrefs being
> > > those of the
> > > version-controlled resource (even though the properties come from the
> > > labelled version).
> > >
> > > This is too confusing.  Al the existing code that people write to
> > > associate
> > > the href with the properties would have to be re-written as
> the reported
> > > properties are from a different resource to the href.
> >
> > No, they aren't. They are from a specific variant of the VCR (as
> > defined by
> > HTTP).
> >
> > > > > a version-controlled resource for which the label doesn't exist?
> > > > > >
> > > > > > See section 8.6, the DAV:must-select-version-in-history
> > > precondition.
> > > > > > It is an error if you request a label that does not exist on a
> > > > > given VCR.
> > > >
> > > > So assume we have /a (collection, not-versioned), /a/b
> > > > (not-versioned), /a/c
> > > > (versioned, having a version labeled "x") and /a/d (versioned,
> > > > without that
> > > > label).
> > > >
> > > > I think we all agree that
> > > >
> > > > GET /a/c
> > > > Label: x
> > > >
> > > > Should return the content of the version selected by the label x
> > > > (including
> > > > a vary header and probably a content-location header).
> > >
> > > Agreed -- I think we specify a Location: header, but whatever
> > > (i.e. resource
> > > location, not content location).
> >
> > I think content-location is correct:
> >
> > "The Content-Location entity-header field MAY be used to supply
> > the resource
> > location for the entity enclosed
> > in the message when that entity is accessible from a location
> > separate from
> > the requested resource’s URI. A server
> > SHOULD provide a Content-Location for the variant corresponding to the
> > response entity; especially in the
> > case where a resource has multiple entities associated with it,
> and those
> > entities actually have separate locations by
> > which they might be individually accessed, the server SHOULD provide a
> > Content-Location for the particular
> > variant which is returned."
> >
> > while the RFC says for location:
> >
> > "The Location response-header field is used to redirect the
> recipient to a
> > location other than the Request-URI
> > for completion of the request or identification of a new
> resource. For 201
> > (Created) responses, the Location is that
> > of the new resource which was created by the request. For 3xx
> > responses, the
> > location SHOULD indicate the server’s
> > preferred URI for automatic redirection to the resource. The field value
> > consists of a single absolute URI."
> >
> > > > GET /a/d
> > > > Label: x
> > > >
> > > > will return 403 or 409 with an error element (precondition
> > > > DAV:must-select-version-in-history failed).
> > >
> > > Agreed.
> > >
> > > > GET /a/b
> > > > Label: x
> > > >
> > > > will just return b's content, and the vary header when
> > present will NOT
> > > > include "Label".
> > >
> > > Can I hedge on the vary: header in the response?  Given that
> > the GET cache
> > > may be invalidated by the resource /a/b coming under version
> > control, and
> > > acquiring a label, I may be inclined to believe that we should
> > > return a vary
> > > header for every label: request for a version-controlled or
> versionable
> > > resource.
> >
> > I think this is right. Which means that vary: label must be set
> > upon GET on
> > *any* resource that is versionable (on a server supporting the LABEL
> > feature).
> >
> > > > Similarily, similar results will be returned for a PROPFIND/depth
> > > > 0 on these
> > > > resources. Note that the response element will be "/a/c" in the
> > > > first case, even if the properties of a version with a different
> > > > URI were reported.
> > >
> > > No.  I think the href must be for the version resource selected by the
> > > label, not the version-control resource at the request-URI.
> >
> > Nope. You can't do that. This breaks PROPFIND. HTTP offers you:
> >
> > - variants (representations) of the resource, which will have the
> > same URI,
> > or
> >
> > - redirects (where the request is redirected to a different URI).
> >
> > You can't have both.
> >
> > > > Finally, we have PROPFIND/depth 1 on /a:
> > > >
> > > > - as /a isn't version-controlled, the label header is ignored
> > for *this*
> > > > resource
> > > >
> > > > - Geoff and I claim that it *should* apply to the members then,
> > > > so we'd get:
> > >
> > > ...and I say it shouldn't apply to members, otherwise the result will
> > > contain properties from resources that are not in the same collection
> > > membership hierarchy, and thereby contravene 2518 (as well as
> > > complicate the
> > > result enourmously).
> >
> > RFC2518:
> >
> > "Consequently, the multistatus XML element for a collection
> resource with
> > member URIs MUST include a response XML element for each member
> URI of the
> > collection, to whatever depth was requested. Each response XML
> > element MUST
> > contain an href XML element that gives the URI of the resource on
> > which the
> > properties in the prop XML element are defined. Results for a
> > PROPFIND on a
> > collection resource with internal member URIs are returned as a
> flat list
> > whose order of entries is not significant. "
> >
>
>
Received on Wednesday, 24 April 2002 10:36:07 GMT

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