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RE: [daniel.kirmse@sap.com: WebDAV/DeltaV: GET on Version Tree]

From: Clemm, Geoff <gclemm@rational.com>
Date: Tue, 11 Dec 2001 10:53:19 -0500
Message-ID: <3906C56A7BD1F54593344C05BD1374B10516742D@SUS-MA1IT01>
To: ietf-dav-versioning@w3.org

   From: Alan Kent [mailto:ajk@mds.rmit.edu.au]

   > From: Kirmse, Daniel [mailto:daniel.kirmse@sap.com]
   > 
   > 1.Suppose you have a resource A.file with a version tree as follows:
   > 
   >            A.file,1
   >               |
   >            A.file,2
   >               /\
   >              /  \
   >             /    \
   >            /      \
   >     A.file,2.1   A.file,2.2
   >          |              |
   >    A.file,2.1.1  A.file,2.2.1
   > 

   > where the version number does not necessarily express the
   > sequence of creation of the versions. All versions are checked
   > in.
   > Suppose a client sends a GET A.file Request. Which version of
   > A.file must be sent as response, A.file,2.1.1 or A.file,2.2.1?

   My understanding is you do not do a GET on A.file. You do a GET on
   a URL. The URL must be bound to a particular version by the server.
   So you get whatever version the URL has been bound to. There are DeltaV
   commands for changing the version a URL is bound to.

I think Daniel just was using A.file as a shorthand for the URL that
identifies a version controlled resource ("VCR") whose version history
is as described.  

A GET on A.file will just return the content of A.file.  If A.file
is checked in, then this content is required to be the same as
the content of the version identified by the DAV:checked-in property
of A.file.  If A.file is checked out, then there may be no version
that has the same content as A.file.

(Note: I'd avoid the term "bound" when talking about the relationship
between a VCR and a version, since this might lead someone to infer
that the VCR is somehow a "pointer" to that version.)

   > 2.I'd like to use server workspace for emulating a development (DEV)
and a
   > consolidation (CONS) source tree of a single source tree. 
   > Suppose I have a source tree. 
   > 
   > 		"/" (root)
   > 		/
   > 	     src
   >            / \
   >           /   \
   >          a.c  b.c
   > 
   > Where a.c and b.c are version-controlled resources.

Does "/" identify a workspace?  Or are /src, /src/a.c,
and /src/b.c "free-floating" VCR's that are not in any workspace?
(Commonly, a system that supports workspaces will have all VCR's
appear in some workspace, but that is not required by the DeltaV
protocol).

   > In the beginning of my development I create a workspace DEV to
   > contain all resources of a certain development.
   > 
   > 		"/" (root)
   > 		/        \
   >            /          \
   >           src         DEV
   >           / \          |
   >          /   \         |
   >         a.c  b.c      src
   >                       / \
   >                      /   \
   >                    a.c  b.c

Note that if "/" is a workspace, then you have the "/DEV" workspace
nested inside the "/" worspace.  Many server implementations will not
allow you to nest workspaces, but it is certainly allowed by the
DeltaV spec.  Note that /DEV/src/a.c is in the /DEV workspace but
is not in the "/" workspace, since a VCR can only be in one workspace.

   > Files a.c and b.c are part of the worksapce and after some time
   > there are version 4 of a.c and version 3 of b.c are candidates
   > for delivery. So I set up a new workspace emulating my
   > consolidation source tree (CONS) as a copy of the DEV workspace,
   > copying the latest version of a.c and b.c to it. (Is it allowed
   > so far?)

   Sounds OK to me...

Well, you need to be a bit careful about terminology.  If you use a
WebDAV COPY to copy your DEV workspace to another workspace, you will
just get a tree of non-version-controlled resources at the destination
of the copy.  This is probably not what you want to do, because you
can't do merges or any other interesting versioning operation on these
non-version-controlled resources.  You probably want to use
VERSION-CONTROL or BASELINE-CONTROL to create version-controlled
resources in CONS corresponding to your version-controlled resources
in DEV.  Note though that Dan's client might present this as a
"copy" operation, even though under the hood, the client is issuing
a BASELINE-CONTROL request, or a sequence of VERSION-CONTROL requests.

   > In my oppinion now a checkin of a.c in DEV and in CONS
   > would produce a branch in the source tree of a.c (right?).

If you have a version-controlled resource in both DEV and CONS for the
version history of a.c, and they both identify the same version in
their DAV:checked-in property, then it is true that if you issue a
CHECKOUT/CHECKIN sequence against both VCRs, then you will create a
fork in the source tree.

   I think that is partially up to the implementation as to what the DetaV
   server did. But it would be reasonable behaviour.

If you CHECKOUT/CHECKIN two VCRs that originally had the same version
in their DAV:checked-in property, then your server would have to
create a fork in the version history for that version.

   > Now suppose a user with a user worksapce /usr/dan who has to fix
   > a bug in a.c both in DEV and CONS. I think it is not allowed to
   > have to versons of a.c in the same workspace (right?), so user
   > dan has to set up two workspace to get this done (right?).

   I think that is correct - or use the UPDATE command (I think it is
   from memory) to change the version a URL points at. But creating two
   workspaces seems reasonable.

I'm not sure what you mean by "set up two workspaces".  You already
have two workspaces (DEV and CONS), so you would make a change in DEV
if you wanted to change DEV and in CONS if you wanted to change CON.
Or are you using DEV and CONS to now mean a "line of descent" (which 
in DeltaV we model as an "activity"), rather than a "workspace"?
It's important to be unambiguous here, since activities and
workspaces have different behaviors.

But as Alan says, you can make a change (create a new version) in DEV 
for a.c, and then just update the VCR for a.c in CONS to see this
new version, if you want to have the bug fixed the same way in both
workspaces.

   > Finally the question is: Is it possible for user dan to copy
   > /DEV/a.c into his workspace or MUST he copy /src/a.c into his
   > workspace? Or the other way around: Is it possible to have a
   > workspace as a source of resources for another workspace?

As above, as long as Dan's client is converting Dan's "copy"
request into the appropriate VERSION-CONTROL request, it doesn't
matter whether he "copies" from /src/a.c or /DEV/src/a.c 
(assuming both these VCRs identify the same version as their
DAV:checked-in property).  In particular, the way Dan's client
will do the "copy" is to get the DAV:checked-in version from
the source of the copy, and then issue a VERSION-CONTROL request
(specifying that version) to the destination of the "copy".

Cheers,
Geoff
Received on Tuesday, 11 December 2001 10:53:55 GMT

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