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

From: Clemm, Geoff <gclemm@rational.com>
Date: Thu, 5 Jul 2001 10:23:50 -0400
Message-ID: <3906C56A7BD1F54593344C05BD1374B1038E14E8@SUS-MA1IT01>
To: DeltaV <ietf-dav-versioning@w3.org>

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

   When you use VERSION-CONTROL to create a new version-controlled
   collection, it (as you described previously) will create a complete
   tree of collection and leaf non-collection resources. No content
   will be retrieved. Then the client must use UPDATE on every single
   binding in the whole tree created to change it to the desired version.
   My comment on performance was not volume of data (you do not download
   the content of the resources), just the number of individual requests
   required. You need at least one HTTP request/response per recource
   in the tree created from the VERSION-CONTROL command.

No, a single UPDATE is sufficient if the configuration you want is
baselined or labeled, and a single MERGE is sufficient if the
configuration you want is the latest in an activity (i.e. along a
single line of descent), or in another workspace.

   However, as soon as you UPDATE the collection to a later version,
   it will then populate one level down in the tree. For every
   internal member, you then need to UPDATE it to the desired version
   (possibly creating new child version-controlled collection
   resources). The client really needs to start from the top and
   recursively do UPDATE requests on each request one by one until you
   get down to the bottom. So there are lots of little requests
   required.

See above.  The server would get just one UPDATE or MERGE request.  It
would pick the default version if your request did not specify a
version for that version history.

   > The "best default choice" is appropriately modeled as a workspace
   > (for the server-workspace packages) or a label (for the
client-workspace
   > packages).

   For server-workspace package how does this work? I create a new
   workspace for the first time, then want to populate it. So no existing
   workspace exists? 

If your "best default choice" is implemented as a workspace, then you
do have to have your /ws/best-default-choice workspace created before
you can specify what your best default choice is for a version
history.  A server that wants to "build in" the best default choice
functionality would create such a workspace when that server is
initialized on a host.

The point here is that the only way to have the "best default choice"
scale is to allow different "best default choices" for different
groups of users.  A simple server can just support a single best
default choice, but the concept needs to be able to scale up for
groups of users for which there is not a single best default choice.

   Or if I have a workspace and want to update everything to the latest
   versisions (since other people have made changes), then again, I need
   to potentially do lots of separate requests.

You can just MERGE one workspace to another, if you want to initialize
one workspace with the contents of another.

   I think the answer is "tough luck" (or use baselines - I have not tried
   to understand them yet).

We try to avoid the "tough luck" answer as much as possible (:-).
In this case, the answer is "MERGE".

   Unless the version history of versions modelled a primary version
   series with other branches off to the side (ala CVS), it is not
   possible to say 'VERSION-CONTROL at this time point for the whole
   tree'.

That is correct, you need either a single BASELINE-CONTROL operation,
or two operations: VERSION-CONTROL followed by either a single MERGE
(for duplicating a workspace or line of descent) or a single UPDATE
(for selecting a label or a baseline).

   I am assuming introducing the concept of multiple linear version series
   is too much for the DeltaV community to swallow in terms of change.

This is covered by the "activity" concept.  Each activity is required
to be linear sequence of versions.  If you want to identify one
activity as your "primary" activity, that is fine (we in fact do so in
our product, we call it the "main" activity).

   It would support the CVS and DMA approaches quite closely. (eg:
   Create version-controlled resources for 'whatever version existed at
   date X' / 'latest version' for the version series called
'primary'/'1.1.1'/
   'with label Y'). It would allow a single VERSION-CONTROL command to get
   the correct version across a hole collection tree. But it is not possible
   with the current simplistic model of versions having predecessors and
   successors. It requires something such as the more detailed model of
   identifying linear series of versions (so you can find the last in a
   linear series - you cannot find the last in a graph and have it make
sense).

If you want to use this concept, you would MERGE the primary activity
into your workspace to get what you want.  But you do need two operations,
a single VERSION-CONTROL (to specify the root of your collection) and a
single MERGE (to indicate what linear series you want to populate the
collection).

Cheers,
Geoff
Received on Thursday, 5 July 2001 10:24:33 GMT

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