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RE: Version-controlled collection resources - I am still missing something

From: Clemm, Geoff <gclemm@rational.com>
Date: Mon, 2 Jul 2001 10:41:27 -0400
Message-ID: <3906C56A7BD1F54593344C05BD1374B1018E2501@SUS-MA1IT01>
To: DeltaV <ietf-dav-versioning@w3.org>
   From: Alan Kent [mailto:ajk@mds.rmit.edu.au]

   I can use VERSION-CONTROL to create a new version controlled
   resource (VCR) by identifying a version resource (VR). If the VR
   holds the versioning information for a collection, then the VCR
   will be a collection resource.

Yes.

   What bindings will be in the VCR collection resource? Will it be an
   empty directory? Or will it automatically have bindings to version
   histories? (and what does this mean??) Or...

Good catch!  The intent was for the semantics of VERSION-CONTROL for a
collection version to be the same as the semantics of UPDATE for a
collection version (see Section 14.12), but this of course should be
stated explicitly.  In particular, the new version-controlled
collection should have a version-controlled member for each version
controlled binding specified in the DAV:version-controlled-binding-set
of that collection version.

So following text should have appeared in section 14.9 (additional
VERSION-CONTROL semantics for version-controlled collections):

 Additional Postconditions:

 (DAV:new-version-controlled-collection): If the request body
 identified a collection version, the collection at the request-URL
 MUST contain a version-controlled internal member for each
 DAV:version-controlled-binding specified in the
 DAV:version-controlled-binding-set of the collection version, where
 the name and DAV:version-history of the internal member MUST be the
 DAV:binding-name and the DAV:version-history specified by the
 DAV:version-controlled-binding.  If the internal member is a member of
 a workspace, and there is another member of the workspace for the same
 version history, the DAV:version of the internal member MUST be the
 DAV:version of that other member; otherwise, the DAV:version MUST be
 the DAV:root-version of the version history.

If nobody has any objections to this text, I'll add this to the
next working draft.

   Basically I am trying to understand how to create a workspace, then
   populate it with with non-checked-out version control instances.
   What commands do I need to do?

You need to do an initial VERSION-CONTROL request to get the
first version-controlled collection into the workspace, and
then do a sequence of MERGE (or UPDATE) requests to populate
the members of that collection with the desired versions.

If you put a collection under baseline-control, you can set the
versions of all the members of that collection with a single MERGE of
a baseline into that baseline-controlled collection.

   If I do a VERSION-CONTROL command,
   I can get a version-controlled-resource referencing a version-resource.

Yes (the version resource is referenced by the DAV:checked-in
property of the VCR).

   I understand this for a non-collection resource. But what about a
   collection resource? I guess I get a collection with bindings to
   version histories(????).

You get a version-controlled collection whose members are 
new version-controlled resources for those version histories
(initially selecting the DAV:root-version of those version
histories).

   Do I then use VERSION-CONTROL to replace the
   bindings to version-history resources with bindings to version-controlled
   resources?

You would use MERGE to adust the DAV:checked-in version of the
internal members.

   Or using VERSION-CONTROL to get a collection, does it
   magically walk the whole collection tree from that point down creating
   version-controlled-resource instances to all the resources in the
   whole collection tree?

A collection version doesn't specify what versions of its members
should be selected, but a baseline (i.e. a configuration version)
does.  So to create a whole version-controlled collection tree in a
single requests from an existing baseline, you can use
BASELINE-CONTROL.

   Hmmm. Not sure if the above makes much sense. Put simply, I have
   a project with a tree of files. I want to create a workspace (for
   server side versioning) then get a read-only copy of all the files
   ("Get Latest Version" in Microsoft Visual Source Safe) in the project.
   I do not want to check them out yet. I want to do that later.
   I just want to read the files then later check out the files I
   actually want to modify. I am not sure of the complete sequence
   of commands to do this. (With an example of such a sequence, all
   my other questions probably go away.)

VERSION-CONTROL /ws/alan/src 
<D:version> <D:href> http://repo/coll-ver/345 </D:href> </D:version>

# assume that coll-ver/345 has bindings named a.html, sub, and othersub
# in its DAV:version-controlled-binding-set

MERGE /ws/alan/src/a.html
<D:source> <D:href> http://repo/ver/4901 </D:href> </D:source>

MERGE /ws/alan/sub
<D:source> <D:href> http://repo/coll-ver/234 </D:href> </D:source>

# assume that coll-ver/234 has a binding named b.html
# in its DAV:version-controlled-binding-set

MERGE /ws/alan/sub/b.html
<D:source> <D:href> http://repo/ver/3244 </D:href> </D:source>

# assume that there is a baseline for othersub

BASELINE-CONTROL /ws/alan/othersub
<D:baseline> <D:href> http://repo/bl/267 </D:href> </D:baseline>

   The DeltaV spec I have says

       14 Version-Controlled-Collection Feature
       Although a collection version only records the version-controlled
       bindings of a collection, a version controlled collection MAY
       contain both version-controlled and non-version-controlled
       bindings. Non-version-controlled bindings are not under version
       control, and therefore can be added or deleted without checking
       out the version-controlled collection.

   So collections can contain both version-controlled and
   non-version-controlled resources at the same time.

Yes, a version-controlled collection can (but note that only
the version-controlled bindings are captured by a collection
version, so the non-version-controlled members are not "shared"
by other workspaces).

   I assume that I can create and delete non-version-controlled resources
   in the directory whether the collection is checked-out or not.

Yes.

   This continues with text talking about Lock Null resources.

       This feature is essential for the support of lock null resources,
       since a lock null resource is a temporary internal member of a
       collection that should only exist for the duration of the lock, and
       should not be captured in the version history of tha coolection.

   If we do not have lock null resources, does this mean that we no
   longer need to be able to create non-version-controlled-resources
   under a version-controlled collection? (My guess this is not the case,
   but it seemed topical.)

There are other reasons to have non-version-controlled bindings.
In particular, if your server supports server-side build management,
then the derived files (e.g. results of compilation or other kinds
of processing) are commonly stored as non-version-controlled
bindings.  Other kinds of derived resources are index resources that
speed up searching within a collection (like the emacs TAG files).

       14.10 Additional CHECKOUT Semantics
       ... If the request has been applied to a collection version, the
       new working collection MUST be initalized to contain a binding to
       each of the history resources identified in the
       DAV:version-controlled-binding-set of that collection version.

   Does this delete references to any other bindings to
   non-version-controlled resources that are in the working directory?
   My guess is not.  But what if there is a collision? (Eg: a
   non-version-controlled resource is created called FOO then the
   collection is checked out which contains a FOO binding. Does the
   CHECKOUT fail? etc.)

Note that applying a CHECKOUT to a collection version is only
done with the client-workspace package.  There you are not checking
out the version-controlled collection, but rather creating a
fresh new working collection, with bindings to version histories
(very different from what happens when you CHECKOUT a
version-controlled collection).

When you CHECKOUT a version-controlled collection, there never
is a collision because a CHECKOUT of a VCC does not change any
of the bindings of that VCC.

BUT, you can create the collision you describe with an UPDATE or MERGE
request.  In this case, the rules in section 14.1.1 apply (the dreaded
"eclipsed-set" that Tim referred to earlier :-).  The rule is pretty
simple though ... if a version-controlled collection has a
version-controlled binding that has the same name as a
non-version-controlled binding, the non-version-controlled binding is
the one that is visible.

   Or, if using VERSION-CONTROL to get a collection resource does
   populate it with all bindings (ie, the working collection is not
   empty), then the only way to get a collision is to have deleted
   the binding before hand (in which case there is probably no danger
   as you probably are not permitted to delete a resource-controlled
   binding if the collection resource is not checked out).

   ps: Boy this can be a tounge/brain twister!

We *really* appreciate you working through all the tricky bits!  The
rest of us have been up and down this road too long to notice the
missing signposts (:-).

Cheers,
Geoff
Received on Monday, 2 July 2001 10:34:57 GMT

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