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Re: Working collections

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Sat, 18 Nov 2000 16:47:56 -0500 (EST)
Message-Id: <200011182147.QAA17391@tantalum.atria.com>
To: ietf-dav-versioning@w3.org

   From: Greg Stein <gstein@lyra.org>

   We need to be able to do a CHECKOUT on a collection version so that we can
   perform operations within the collection and on the collection itself.
   In Subversion, I've been planning to do a CHECKOUT on a parent collection
   version resource, which will return a location such as:
       http://host.name/repo/$svn/wrk/100.3

We should first confirm that we agree on the semantics of a collection
version and a collection version selector, namely, that each member of
a collection version is a version history,  while each members of a
collection version selector is either an unversioned resource or a
version selector.

Assuming we agree on that, then if we are going to allow a "working
collection" (i.e. the result of checking out a collection version),
then we need to decide what the members of a working collection would
be.

By analogy with collection versions, the members could be version
histories.  By analogy with collection version selectors, the members
could be unversioned resources or other working resources.  Or we
could make up completely different semantics for a working collection
that are distinct from those of either collection versions or
collection version selectors.  I'd like to avoid this third alternative,
since it is likely to cause additional complexity in what is already
the most complex part of the protocol.

   I can then do the following:
       PUT http://host.name/repo/$svn/wrk/100.3/newfile.html
   or even:
       COPY http://host.name/repo/somedir/foo.c
       Destination: http://host.name/repo/$svn/wrk/100.3/foo.c

If working collections were like version selectors, then this
would be fine since then working collections could have 
unversioned members.

If working collections were like collection versions, then this
would be illegal since only version histories can be members.

       (or a MOVE if the source's parent is checked out)

A MOVE is fine, if the MOVE was from another working collection,
but if the MOVE was from a non-versioned collection, then you
run into the same problems as PUT.

   The working resource for the collection is also handy for deleting or for
   replacing the collection:

       DELETE http://host.name/repo/$svn/wrk/100.3
       (note that this request also requires a checked-out parent)

This is fine.

       COPY http://host.name/repo/somedir/
       Destination: http://host.name/repo/$svn/wrk/100.3
       Overwrite: T

This wouldn't work, because deleting a working resource (as is done by
an Overwrite:T) cancels the checkout.  You would need to use the new
"update" value for the Overwrite header.

   DELETE of a member is a CHECKOUT of two items: the thing to DELETE and the
   parent collection.

Only the parent collection needs to be checked-out in order to
DELETE a member of that collection.

   Without being able to do a CHECKOUT on a collection, there wouldn't be a way
   to do any of the above.

You could just use a VERSION-CONTROL request to create a new version
selector whose target is the desired collection version.  Then you can
do all your operations on that version selector.  It is one extra round
trip, but if that really matters, we could easily add a "DAV:keep-checked-out"
option to the VERSION-CONTROL request.  This would allow us to avoid
all the extra complexity that would result from having two ways to manipulate
versioned collections.

Cheers,
Geoff
Received on Saturday, 18 November 2000 16:48:39 GMT

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