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Re: DAV:checked-out

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Fri, 6 Oct 2000 18:25:25 -0400 (EDT)
Message-Id: <200010062225.SAA11502@tantalum.atria.com>
To: ietf-dav-versioning@w3.org
   From: Greg Stein <gstein@lyra.org>

   > <boris> The change was made because in the old spec, servers that 
   > supported workspaces would be confusing for clients because they replaced
   > version selectors on checkout whereas other servers created working
   > resources at a new URL. </boris>

   But then the second client to check the thing out would be attemping to
   check out a WORKING resource. That can fail without demanding this whole
   "single checkout" mechanism.

Yes, but we believe that a client needs to be able to control whether
there is an "in-place" checkout (i.e. the version selector is now
checked out) or whether a new working resource (at a different URL) is
created, leaving the request-URL a checked in version selector.

So you just indicate what you want, by including or omitting the
DAV:target parameter to the CHECKOUT request.

   > The scenario is:
   > 
   >   - Joe creates and activity, checkouts out /foo into that activity, and
   >     begins updating it.
   >   - Jane does likewise.
   >   - One or both merge the activity
   > 
   > <boris> I can see two possibilities for mapping this scenario to deltaV:
   >  In the first possibility, which does not use workspaces (or just one),

   I'm not using workspaces, and don't plan to. They aren't needed in my
   scenario, as working resources at arbitrary URLs are quite acceptable.

That's fine.  Workspaces are of course totally optional.
Boris was just being complete in his response (:-).

   >  both Joe and Jane check out /foo using 
   >    <DAV:checkout><DAV:target/></DAV:checkout>
   >  which creates a working resource at a server-generated URL. The merge 
   >  takes care of setting the target of the version selector at /foo. Note
   >  that the only difference to the way it was spec'd before is that the
   >  version selector's target is not updated when you check in a working
   >  resource. But this probably is what you want anyway, since you use
   >  activities and merging to update the shared state (and not the check in
   >  operation).

   This would appear to work since a version resource can have multiple hrefs
   in its DAV:checkout-set property.

Yes.

   >  The second possibility is to use three workspaces, a common one, and a 
   >  private one for each developer. A checkout, this time without the
   >  <DAV:target/>, only affects the private workspace, and you can use
   >  activities and merge to update the shared state in the common workspace.
   > </boris>

   I'm using activities to operate as a Change Set. Now you're also saying that
   I must create/destroy a Workspace, too.

No, no, no!  He was just saying that there is a *second* different
way to get the same effect.  If you liked the first way, just ignore
the rest of his message (:-).

   No way. DeltaV is just broken if I
   must do something like:

       MKWORKSPACE
       MKACTIVITY
       CHECKOUT /foo
       PUT /foo
       MERGE /act/123
       DELETE /act/123
       DELETE /ws/123

No, the second approach is one where each person creates a workspace,
and lives in that workspace from then on (or at least, for quite a
while).  You create that workspace once, and then do all your
checkout/checkin's on version selectors in that workspace.  You would
only create a second workspace for yourself if you were working on two
projects at the same time, in which case you'd create one workspace
for each project you are concurrently working on.

   We're talking a very transitory operation, and building up a workspace for
   that isn't right. I'm also not a fan of workspaces to begin with (I don't
   like mutating resource types in place).

Then you'll be happy that you no longer mutate resource types for an
in-place checkout (:-) ... you just change the state of the version selector
from checked-in to checked-out.  (But you are of course free to create
a working resource instead).

   -------

   In John Vasta's email, he said the DAV:checked-out property on the version
   selector could be used to diff the working resource against what was checked
   out. That is the wrong approach. The DAV:checked-out should be on the
   WORKING resource, not the version selector. That is the right place for it,
   and it provides exactly the same value. If you are using workspaces, then
   the (in-place) working resource will have that property.

Working resources are by (the current :-) definition not in-place.
An "in-place working resource" is a checked out version selector.

   -------

   DAV:checked-out on a version selector is not right. It should be on a
   version resource and on a working resource.

   I should be able to multiply-checkout a version selector, and have it imply
   the target for checkout each time.


   Oh. Geez... and I just saw in the spec. DAV:target *DISAPPEARS* from the
   version selector when it gets checked out?

   No. No. No. No. <repeat>

As you said above, it is brain dead to mutate the resource type of
a resource "in place", so we don't do that anymore (:-).  I thought
you'd be pleased (or at worst, not care :-).

   If somebody goes and checks out a version selector, then all the clients
   will now need to read *two* properties to try and reach the target version
   resource?

That's exactly what would have happened whenever you had an "in-place"
checkout.  Before the CHECKIN, you had a resource with a
DAV:target property.  After the CHECKIN, you had  a resource with
no DAV:target property, but with a DAV:checked-out property.

Before we said it also magically changed its type.  We don't
say that anymore.

The meaning DAV:target is very different from the meaning of
DAV:checked-out, and reflects the state change from checked-in to
checked-out.

   No way. What if I'm trying to do a property report and use
   DAV:target to link over to the version resources to fetch their data?

You expected to be able to do that to a working resource?  It has no
DAV:target property, so you were always out of luck if you wanted to
use the same PROPFIND on a checked in and a checked out resource.

   Oops.
   That doesn't work since DAV:target doesn't exist any more on some of the
   version selectors.

It never did, after they were "replaced" by an "in place" working resource.
It's just that now we make it clear (:-).

   PROPOSAL:

     DAV:target is always defined on a Version Selector

checked-in version selector, sure.

     Working Resources have a DAV:checked-out property

As do "checked-out" version selectors.

     Version Selectors never have a DAV:checked-out property

What about when they are checked out?

     Version Resources retain their DAV:checkout-set, but drop the bit about
	 version selectors having a DAV:checked-out property

But what about when they *are* checked out?

     CHECKOUT does not manipulate the Version Selector

It always did (i.e. the "in place" CHECKOUT).  It just wasn't obvious
before.

     Put the language back in that says a CHECKOUT on a Version Selector
	 replaces it with a Working Resource (which seems to be part of what is
	 happening here)

How is that any better?  The bottom line is that the properties on
the request-URL change as a result of the CHECKOUT. 

Keep in mind that all we did to the spec was a mechanical query/replace
of "in place working resource" with "checked out version selector".
No change at all in any of the semantics.  If you didn't think that
it acted this way before, that is one of the main reasons why we
changed the description, because the old way of describing it hid
some very essential semantics that are now exposed.

Cheers,
Geoff
Received on Friday, 6 October 2000 18:25:55 GMT

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