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RE: Autoversion confusion

From: <Tim_Ellison@uk.ibm.com>
Date: Wed, 7 Feb 2001 09:21:26 +0000
To: ietf-dav-versioning@w3.org
Message-ID: <802569EC.00335708.00@d06mta07.portsmouth.uk.ibm.com>


> I take your point about the checked-out version only
> being created when the PUT is issued.  Still, some
> confusion remains.

Ok, but we are converging!

> The spec frequently makes statements like: "The resource
> MUST have a DAV:checked-in property that identifies the
> new version.  The content, dead properties, and DAV:resourcetype
> of the new version MUST be the same as those of the resource.  "
> Also: "Although the content and dead properties of a checked-in
> version-controlled resource are required to be the same as
> those of its current DAV:checked-in version..."

These statements are made in the context of a checked-in version-controlled
resource.

> OK, so based on my reading of this text and others, I assumed
> that the VCR ALWAYS had the body and the content of the last
> checked-in version, whether or not the VCR was checked-out.

No, when a version-controlled resource is checked in it has the same
content and dead properties (C&DP) as the version identified in the
DAV:checked-in property.  However, when a version-controlled resource is
checked-out, its C&DP are not necessarily the same as any version.

The moment it is checked out on the server, the VCR will have the same C&DP
as the version identified by the DAV:checked-out property, but the nature
of a checked-out VCR is that it can be modified, so subsequent PUTs etc.
will mean it is no longer the same as the DAV:checked-out version.

Take another look at Section 2.1.2 Modifying a Version-Controlled Resource,
in particular the diagram that shows the VCR moves to state S3 after the
successful PUT.  S3 is not captured as a version until the CHECKIN.  Of
course, there could have been multiple PUTs and/or PROPPATCHes between the
CHECKOUT and CHECKIN.

> Nowhere does the draft state otherwise, e.g. that a checked-out
> VCR has the body and properties of the checked-out version.

...because that is untrue.  A VCR is a first-class resource, with content
and properties.  When it is checked out it is "open for change".  There is
no checked-out version associated with a checked-out VCR.

The only way to get a checked-out version is by sending CHECKOUT to the
version itself (i.e., using the version URL, or a Label: header). The
checked-out version is called a working resource (not a checekd-out VCR).
Creating working resources is optional for the server (the
"working-resource" option).

> Clearly, you and perhaps the other authors have a different
> mental model of the way this works, but nowhere in the draft
> is this stated.  I admit that 2.1.2, on careful viewing, does
> imply that the checked-out VCR shows the body and properties
> of the latest version, but I want a normative statement.

A checked-in VCR will always have the same C&DP as the DAV:checked-in
version.  Sending it CHECKOUT essentially flips a read-only bit to
read/write (ok and jiggers the live properties a bit) and that's it!
Simple eh?

Tim
Received on Wednesday, 7 February 2001 04:21:38 GMT

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