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Re: live props on a VCR

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Mon, 18 Dec 2000 15:24:03 -0500 (EST)
Message-Id: <200012182024.PAA02619@tantalum.atria.com>
To: ietf-dav-versioning@w3.org

   From: Greg Stein <gstein@lyra.org>

   On Mon, Dec 18, 2000 at 12:07:39AM -0500, Geoffrey M. Clemm wrote:

   >    From: Greg Stein <gstein@lyra.org>
   >    I want to get the DAV:version-name from the VCR (rather than
   >    issue a second PROPFIND against the DAV:target of the VCR).

   > You could just use the property report to avoid the extra
   > roundtrip, i.e.  to get the version-name of the target of a vcr:
   > 
   > REPORT /whatever HTTP/1.1
   > ... some headers ...
   > <D:property-report xmlns:D="DAV:">
   >   <D:target>
   >     <D:version-name/>
   >   </D:target>
   > </D:property-report>

   hehe... that will be even worse. The PROPFIND that I'm using is a Depth:1
   request. I'm fetching the props for a whole bunch of resources. If I
   switched to a REPORT, then I'd need to do a PROPFIND on a collection to get
   all the children, then a PROPFIND/REPORT to link thru the target to get the
   props off the version resource. Blarg...

Actually, REPORT takes a Depth header, so you could get all the
properties you need in one REPORT request.

It occurs to me that the current spec needs some more verbiage around
REPORT with Depth.  It currently just says "if a Depth header is
specified, a 207 multistatus MUST be returned".  It should say that
the report results should be marshalled in the "prop" elements of the
207 multistatus.  We could define our own 2xx "multi-report" return
value, but just re-using the 207 seems simpler.

In fact, if people care, we could extend the REPORT method to allow
you to request multiple reports at the same time.  Anyone want to
do that while I'm in there making changes?

   What would be neat is a collection property providing the URLs of its
   members. You could then do a property-report kind of like:

     REPORT /the-collection HTTP/1.1
     ... some headers ...
     <D:property-report xmlns:D="DAV:">
       <D:member-set>
	 <D:target>
	   <D:version-name/>
	 </D:target>
       <D:/member-set>
     </D:property-report>

   :-)

   (this would also be nice in that I wouldn't have to filter out the PROPFIND
    result for the collection itself... I'd only get the internal members)
   [ and I'm not truly suggesting this new property, but it is certainly an
     interesting item to ponder... ]

Except for the filtering out the collection itself,
this is what you can do with a Depth header on the REPORT.

And yes, it is pretty silly that there is no Depth value that says
"just my immediate children".  That's probably what Depth=1 *should*
have meant.  Oh well ...

   Well, the simple issue in my mind is "I've got this (VC) resource here, but
   I don't know what it is [without the version-name]." There is a non-trivial
   amount of work to go and fetch that version-name; if it had simply been
   exposed via the VCR, then I'd be fine.

   I'd think the following properties are "important" to have appear on the
   VCR, and a statement that they MUST be the same:

     DAV:version-name
     DAV:checkin-date
     DAV:comment             (*)
     DAV:creator-displayname (*)
     DAV:version-history
     DAV:version             (+)

   (*) actually, the VCR could define these itself, so these might be confusing
   to have appear on the VCR.
   (+) this is unchanging, but is just a copy of the DAV:target prop  (??)

   There are some informational properties: checkin-fork, checkout-fork, and
   mutable; I don't have any feelings about them. I'm also not going to suggest
   the *-set properties, since they could be computed and will change from time
   to time.

   The properties above are all (typically) immutable. It would be nice to have
   a MUST for these, and then a SHOULD for others (or even punt the others).
   Punting all others would satisfy Geoff's concern about people blurring the
   distinction between the resources. Avoiding the *-set properties will also
   help out with the remote system issue.

If using the DAV:property report (and Depth) does what you need
(i.e. get version info in a single simple query),
it would be simpler to leave all this out of the protocol.

Cheers,
Geoff
Received on Monday, 18 December 2000 15:24:48 GMT

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