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RE: Confusion: Removing a resource from version control

From: Clemm, Geoff <gclemm@rational.com>
Date: Tue, 12 Jun 2001 21:08:22 -0400
Message-ID: <3906C56A7BD1F54593344C05BD1374B10350A032@SUS-MA1IT01>
To: ietf-dav-versioning@w3.org

   From: John Hall [mailto:johnhall@evergo.net]

   I was not planning on implementing a version-history feature.  I
   see absolutely no problems with supporting the working resource
   feature with anything I've said.

Rick's point was that if you are also supporting the workspace
feature, since you will have many version-controlled resources for the
same version history, you need to decouple the lifetime of a version
history (and version) resource from the lifetime of any of the
version-controlled resources that might refer to it.

The protocol has to be consistent in how it acts under any combination
of features, so you cannot have a DELETE of a version-controlled
resource do incompatible things depending on what feature set is
supported by the server.  (Well, you could, but then writing an
interoperable client becomes infeasible).

   I wasn't planning on supporting
   workspaces, but I don't see any problems there that aren't inherent
   in being able to delete individual versions.

If a client explicitly deletes a version resource, it knows what
it is doing.  In the case of your client that wants to destroy
all old versions, it can certainly do so (and in fact, if your
server supports version history resources, it can do so by issuing
a single delete against the version history resource).

But a versioning *unaware* clients will also be issuing a DELETE
against a version-controlled resource on a versioning server that
supports workspaces, and reasonable behavior must result.  Blowing
away all versions of that resources from all other workspaces is not a
reasonable result.

   Although you can keep an object around that allows you to retrieve
   the version history of a completely deleted resource, I don't
   understand how that can be done without eventual name collisions.

Keep a counter, or any other kind of GUID generator.  According to the
protocol, each new version MUST be given its own unique URL.  A long
email thread about 3 months ago let to this consensus, although not
unanimous, decision.

   Say I create foo/bar.txt as a version controlled resource.  If I
   wanted a separate version history object, I could put it in some
   place like /vhist/foo/bar.txt Now someone wants to delete
   foo/bar.txt -- OK, I delete it but not /vhist/foo/bar.txt

   That works until someone tries to create a new foo/bar.txt that
   they wish to be a version controlled resource.  I have a collision
   with /vhist/foo/bar.txt and THIS foo/bar.txt is completely distinct
   from the original.

This just means you have to add some GUID to the version history
resource (and the version resource) URL's.  So you'd keep a counter
at /vhist, bumping it each time you create a new version history
resource.  So the version history for foo/bar.txt would be
something like /vhist/foo/bar.txt;3456 while the later version
history for foo/bar.txt would be something like /vhist/foo/bar.txt;8322

All the details are in the old email thread, but the basic reason
is that the ability to have reliable URL's to old versions outweighed
the additional implementation cost of requiring that GUID's be
added to version history and version URL's.


   From: Rick Rupp [mailto:Rick.Rupp@merant.com] 

   I disagree that version history should be deleted if you delete the
   version controlled resource. Section 5 of the draft clearly states
   the version history resource exists in a server defined namespace
   and therefore is unaffected by any deletion or movement of a
   version controlled resource.  If you require the version history to
   be deleted you will cause serious problems for a server that
   supports the workspace and working resource feature.

   From: John Hall [mailto:johnhall@evergo.net] 

   When you DELETE a version-controlled resource, I strongly believe
   that all information for that VCR and all versions already created
   should go to the great bit bucket in the sky.  As I understand your
   formulation, I would have severe problems in modifying my DAV
   server (with versioning support) to support DELTAV using this
   behavior.  I would prefer this formulation / behavior:

   "In order to remove a resource at a given URL from version control,
   the client can replace the resource under version control with a
   non-version-controlled copy of that resource.  For example, a
   client can COPY the version-controlled resource to a temporary
   location, DELETE the version-controlled resource, and then MOVE the
   copy from the temporary location back to the original URL.  Note
   that the versions already created for the version-controlled
   resource will NO LONGER BE AVAILABLE.  If you wish to remove a
   resource at a given URL from version control while also retaining a
   previous revision history, then you should MOVE the resource to a
   new save location and COPY the current version back to the original


   My formulation is based explicitly on the idea that some
   implementations and some customers are not keeping track of legal
   documents and therefore deleting old versions is highly desired if
   not required.  A server shouldn't be forced to keep data that a
   client is willing to specifically state that it doesn't want.  I
   think a far better manner of achieving your goals is simply to
   allow the VERSION-CONTROL method to turn version-control for a
   resource at a given URL off (if supported by the server).  That
   allows you to achieve your above objectives (no new versions, but
   keep the old ones at the same URLs) without changing the usefulness
   of the DELETE command.
Received on Tuesday, 12 June 2001 21:03:20 UTC

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