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Re: Parallel Development

From: Tim Ellison <Tim_Ellison@uk.ibm.com>
Date: Thu, 13 Dec 2001 12:54:02 +0000
To: "Ietf-Dav-Versioning (E-mail)" <ietf-dav-versioning@w3.org>
Message-ID: <OFE849176D.9E898CCE-ON80256B21.004449B1@portsmouth.uk.ibm.com>
"Kirmse, Daniel" <daniel.kirmse@sap.com> wrote:
> HI,
> 
> its getting complicated! First of all many thanks to everyone
> anwsering my questions so far! It helped me a lot.
> 
> So next question:
> 
> Scenario:
> Suppose a development environment where the development
> codeline is kept in a workspace. Within this Workspace
> there is a VCR /DEV/a.c the checked-in property points
> to version  V1.

Ok, so there are two distinct resources, a version-controlled resource at
    /DAV/a.c

and a version resource at some server-generated URL, let's say,
    /versions/vh1/r23

The checked-in property of the version-controlled resource has a value 
that is the URL of the version.  This means, "the version-controlled 
resource is checked-in (i.e. `immutable`) and it has identical (i.e. a 
true copy of) content and dead properties as the version whose URL is in 
the DAV:checked-in property"  Note that the version-controlled resource 
may have different live properties to the version resource.

> Now there is a checkout of the checked-in version of /DEV/a.c
> into a working-resource WR1.

Just to be pedantic, a version is not checked-in (or checked-out for that 
matter), but applying CHECKOUT to a version creates a new working resource 
with the same content and dead properties as the version.

> In my understanding of DeltaV the checked-in property of the
> VCR is not changed by this action.

Correct, the version-controlled resource is unaffected by the creation of 
the working resource.  It remains a checked-in version-controlled 
resource.

> Now another checkout of the checked-in version into a working-
> resource WR2 is done (i.e. two developer working parallel on
> the same source). Rigth so far?

Sure (assuming liberal fork control) you can create more working resources 
by applying CHECKOUT to the version resource.

> If not, is there a way in DeltaV to get done the behavior
> described below?

> Now WR1 is checked in. WR1 disappears the version history
> (VH) of /DEV/a.c contains a new version V2 that is a descendant
> of V1.

Correct.

> In my understanding the checked-in property of the
> VCR is set to V2 during this checkin. Still right?

Nope (we were doing so well up to this point :-)

The version-controlled resource is not updated since there is no tie 
between the working resource created by checking out the version, and the 
version-controlled resource.  So in this scenario, the version-controlled 
resource would still have the same content and dead properties as the 
version V1.

If you did want to update the version-controlled resource there are two 
ways to do this.

(1) Rather than check-out the version to create a working resource you 
could have just checked-out the version-controlled resource 'in-place'. 
You would then modify the version-controlled resource (PUT, PROPPATCH, 
etc.) and check-in the version-controlled resource to create a new 
version.  However, modifying the resource in-place obviously means that 
other clients would see your work in progress.  In the trivial case this 
is state that you didn't want to version because it was incomplete; but 
more seriously it could be a state that is inconsistent because there is 
no way to modify the properties and content simultaneously (imagine a 
"FOOBAR:last-modified-by" property).  So the alternative way is...
(2) send CHECKOUT to the version-controlled resource _with_ a 
DAV:apply-to-version flag.  Now you have a (hidden) working resource that 
is coupled to the version-controlled resource, as evidenced by it's 
DAV:auto-update property.  Since the working resource is effectively 
hidden from other clients, you can modify the content and properties, 
numerous times, and finally CHECKIN the working resource.  This check-in 
will create the new version, delete the working resource, *and* update the 
version-controlled resource identified by the DAV:auto-update property.

> Now WR2 is checked in. Checkin fork is forbidden. Because there
> is a descendent to V1 allready and the checkin fork is forbidden.
> So a merge must be forced (how?). After that done the checked-in
> property of the VCR points to the merged version of V2 and the
> checked in version of WR2. Right?

So now, hopefully, you see that you can't get into this mess<g>.

> Background:
> I have a development codeline. A file to edit is a VCR. I want
> the possibility of two (or more) developers working parallel
> with this file. But I want them to do a merge of their work at
> the second checkin (the checkin of the first developer causes
> no problems).

So you would have the DAV:checkin-fork property set to DAV:forbidden for 
each version to force the second checking to fail, and force a merge.

> And I want the VCR point to the most current checked-in version
> of its VH automatically. Is this achieveable?
> I think it must be, since this is what can be done using
> Perforce.

Again, by checking out the version 'through' the version-controlled 
resource, i.e. by using <DAV:apply-to-version/> you can get the 
DAV:auto-update behaviour described above.


Regards,
Tim
Received on Thursday, 13 December 2001 08:18:55 GMT

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