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AW: how to perform undeletion

From: Sohn, Matthias <matthias.sohn@sap.com>
Date: Mon, 18 Mar 2002 16:48:11 +0100
Message-ID: <FAFE609CB754D311B60C0008C75D35560999D583@dbwdfx14.wdf.sap-ag.de>
To: "Ietf-Dav-Versioning@W3. Org" <ietf-dav-versioning@w3.org>
      I think when the resource version to be revived in order to
      undelete the resource has been found the undelete operation can be
      done in the following way :
      - check out the collection which shall contain the resource to be
      this yields a working collection which is bound to an activity
      (since I want to track all changes in activities)
      - issue VERSION-CONTROL on the resource version contained in the
      old collection version before the deletion of the resource took
   A collection version does not contain resource versions, it contains
   a DAV:version-controlled-binding-set property that contains a set of
   name/version-history pairs.

Sorry it seems that my sentence was too sloppy. 
- I meant that by using some report provided by my server I can find out 
to which version of the deleted resource the VCR has pointed to just 
before the resource has been deleted. 
- Since the resource has been deleted before the undeletion is done
there is no VCR for the version history of the deleted resource in 
my workspace. By issueing VERSION-CONTROL on the version I want to put 
back to life I thought I can create a new VCR in the checked out collection
(which belongs to my workspace) which will then point again to the 
same version the old VCR pointed to before it has been deleted.
   Also, you don't issue VERSION-CONTROL requests to members of 
   a working
   collection, because a working collection does not contain
   version-controlled resources (and VERSION-CONTROL creates a
   version-controlled resource).  The VERSION-CONTROL request is used to
   restore resources to checked-out collections (i.e. to 
   collections that
   can be checked-out in place), not to working collections.

I don't want to issue VERSION-CONTROL to a member of the working
collection but to the resource version I want to revive in order 
to create a new VCR for it. This version I found using a report. 
I only want to checkout the target collection in order to allow the
recreation of the resource (which shall become a member of 
the checked out collection).
        In this request specify the URL under which the VCR for 
   the resource to
        undeleted shall reappear.
      - check in the activity containing the working collection 
   which now has a
        binding pointing to the newly created VCR for the 
   undeleted resource.
   Working collections cannot contain a VCR.
      - if since the resource has been deleted another resource has been
        with the same URL the VERSION-CONTROL request given 
   above will fail. 
        In this case the client has to reissue VERSION-CONTROL 
        another request URL which uniquely identifies the URL 
   of the resource 
        to be undeleted.
      Is this approach compliant to the DeltaV spec ?
   No, with working resources, you have to CHECKOUT a collection version
   that identifies the version history of the desired version in its
   DAV:version-controlled-binding-set.  Then you can MOVE that version
   history from that working collection into the destination working
   collection, DELETE the source working collection, and then CHECKIN
   the destination working collection.
Huh, I feel this partial move is ugly. 

First this needs 5 requests to do a simple undeletion:
- two CHECKOUTs (of the source and target collection versions) 
- (partial) MOVE 
- DELETE (or UNCHECKOUT) on the source working collection 
- and a CHECKIN on the target collection. 

In addition this would require that MOVE is not an atomic
operation (either done completely or not at all). If MOVE is
not atomic I expect that the probability of inconsistencies 
on the server will increase if some client issues a similar 
partial MOVE for a different purpose. Since we use a stateless
protocol it's no option for the server to wait for the DELETE
and CHECKIN until the transaction doing the MOVE is committed.
Without waiting for DELETE and CHECKIN the server has no chance
to find out that this request sequence is an undelete operation 
(which should be atomic as well).

I would prefer if there is some solution which only needs CHECKOUT 
and CHECKIN of the target collection (this seems to be necessary 
with versioned collections) and only one atomic command (e.g. UNDELETE 
or VERSION-CONTROL with additional semantics) which does recreate 
the deleted VCR and ensures that the same version is revived which 
has been in the workspace just before the resource has been deleted. 

This would mean 3 requests instead of 5, less chance for 
inconsistencies (since MOVE is atomic) and clearer semantics 
for the sake of an additional method (or additional semantics 
Received on Monday, 18 March 2002 10:48:47 UTC

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