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RE: Replacing the Label header with a DAV:labeled-version report

From: Julian Reschke <julian.reschke@greenbytes.de>
Date: Sun, 7 Jul 2002 20:49:03 +0200
To: "Clemm, Geoff" <gclemm@rational.com>, "'Deltav WG'" <ietf-dav-versioning@w3.org>
Message-ID: <JIEGINCHMLABHJBIGKBCGEGMEOAA.julian.reschke@greenbytes.de>

> From: ietf-dav-versioning-request@w3.org
> [mailto:ietf-dav-versioning-request@w3.org]On Behalf Of Clemm, Geoff
> Sent: Sunday, July 07, 2002 1:34 AM
> To: 'Deltav WG'
> Subject: RE: Replacing the Label header with a DAV:labeled-version
> report
>
>
>
>    From: Julian Reschke [mailto:julian.reschke@greenbytes.de]
>
>    > From: Clemm, Geoff
>    >
>    > Julian didn't like the marshalling of this report, because it
>    > makes it look like the properties are those of the VCR, when they
>    > actually are properties of the version
>
>    Yes, that's the problem, and I fear the new format doesn't address
>    this.
>
>    If the multistatus/response format is re-used for a REPORT (basically a
good
>    thing), it must not break the existing semantics, in particular:
>
>    - the properties reported must actually be the properties of  the
resource
>    identified by the reported URI (DAV:href) and
>    - the properties reported actually must be properties (!).
>
>    If this is not the case, the response seems to indicate that there's a
>    DAV:labeled-version-report property, which isn't the case.
>
> If this is a problem, it is a problem with the 3253 definition of REPORT.
> In particular, section 3.6 states:
>
>    "If a Depth request header is included, the response MUST be a 207
>    Multi-Status.  The request MUST be applied separately to the
>    collection itself and to all members of the collection that satisfy
>    the Depth value.  The DAV:prop element of a DAV:response for a
>    given resource MUST contain the requested report for that resource."
>
> So according to 3253, the DAV:prop elements MUST contain the requested
> report (as if it were a property).

Good catch. So, taking both RFC3253 and RFC2518 in account, the requested
report must be contained inside DAV:prop, and DAV:prop must contain WebDAV
properties of the resource identified by DAV:href.

This works fine for things like DAV:version-tree, but obviously fails here,
so we need to find a resolution.

> Since this was not considered a problem during any of the reviews of
> 3253, I'd need to hear some compelling reasons why this marshalling
> has become a problem.  In particular, there is no rule that I know of

*I* didn't consider this a problem because none of the reports defined by
RFC3253 actually breaks RFC2518 semantics -- so everytime the multistatus
format is used, the contents of DAV:prop actually *are* WebDAV properties.
So if the *intent* of the text you quoted is to allow *arbitary* reports to
be marshalled *inside* DAV:prop, why wasn't this feature used by any of the
reports defined in RFC3253 (or ACL)?

> that states that the interpretation of a DAV:multistatus element must
> be the same in all contexts in which it appears.  I know that this is
> definitely not the case for other XML elements used by WebDAV (e.g.
> the way the property elements are used in the request and response
> bodies of a PROPPATCH differ significantly).

That's correct, but I don't think that's the point. When people see a
multistatus response body, up until now they *always* could assume that
something that they see inside DAV:prop actually *is* a WebDAV property of
the resource identified by DAV:href. In particular, one would assume that if
it appear inside a DAV:response/DAV:propstat/DAV:prop element, you can also
query it using PROPFIND.

Besides: every time you define a report-specific element for inclusion into
DAV:prop, you basically block any usage of this name as "real" WebDAV
property. In this particular case, using DAV:labeled-version-report as
"container" element makes it impossible to actually have a property called
DAV:labeled-version-report (and to have it returned by this report). While
this may not seem to be a real-world problem here, it would mean that an
ambiguity is introduced into the namespaces of WebDAV property names  --
suddenly there's an overlap with marshalling elements for specific reports.

So why not use a marshalling format that has none of these problems?

>    So how about properly extending the response element, for instance:
>
>      <?xml version="1.0" encoding="utf-8" ?>
>      <D:multistatus xmlns:D="DAV:">
>
>        <D:response>
> 	 <D:href>http://www.webdav.org/folder/</D:href>
> 	 <D:labeled-version-report>
> 	   <D:href>http://repo.webdav.org/his/23/ver/V5</D:href>
> 	   <D:propstat>
> 	     <D:prop>
> 	       <D:version-name>V5</D:version-name>
> 	     </D:prop>
> 	     <D:status>HTTP/1.1 200 OK</D:status>
> 	   </Dpropstat>
> 	 </D:labeled-version-report>
> 	 <D:status>HTTP/1.1 200 OK</D:status>
>        </D:response>
>
>       <D:response>
> 	 <D:href>http://www.webdav.org/folder/foo.html</D:href>
> 	 <D:labeled-version-report>
> 	   <D:href>http://repo.webdav.org/his/84/ver/V8</D:href>
> 	     <D:propstat>
> 	       <D:prop>
> 		 <D:version-name>V8</D:version-name>
> 	     </D:prop>
> 	     <D:status>HTTP/1.1 200 OK</D:status>
> 	   </D:propstat>
> 	 </D:labeled-version-report>
> 	 <D:status>HTTP/1.1 200 OK</D:status>
>        </D:response>
>
>      </D:multistatus>
>
> That would be fine with me (and arguably is cleaner than what is

...thanks...

> defined in 3253), but it is inconsistent with 3253, so unless there

Why would that be inconsistent with RFC3253? The format you proposed earlier
definitively is inconsistent with RFC2518, and I'm not aware of another case
in RFC3253 that has this problem.

> is something seriously wrong with the 3253 marshalling, I think
> consistency is more important here than aesthetics.

I think the RFC3253 marshalling as explained by you in seriously
inconsistent with RFC2518 *and* not very aesthetical. I'm happy it hasn't
been used before :-) I have the feeling I'm overseeing something, and I'm
sure you'll educate me...
Received on Sunday, 7 July 2002 14:49:12 GMT

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