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Core versioning issues and nits

From: Lisa Dusseault <lisa@xythos.com>
Date: Thu, 1 Feb 2001 20:21:49 -0800
To: <ietf-dav-versioning@w3.org>
Message-ID: <CNEEJCPIOLHKIOFNFJDPAENKCCAA.lisa@xythos.com>

I've had a fresh pair of eyes (thanks Barry!) look at the core
versioning sections of
http://www.webdav.org/deltav/protocol/draft-ietf-deltav-versioning-12.ht
m, and here is the list of issues -- often things which a pair of
reasonably intelligent folks couldn't reliably infer from the draft, or
things in core which refer to or require things outside of core.

1) URLs

One fact: The draft currently defines versions, version histories, and
version-controlled "things" as resources (not, for example, as URLs).
One more fact: The definiton of resources in 2518 states that a URLs
which differ only in their parameter set MUST refer to the same
resource.  When I add one and one together, my value for "two" is that
it's illegal to take a base URL to refer to a VCR, and add parameters to
get individual versions and VHRs.

That would mean we cannot have URLs of the form (partial URLs shown
only):
VCR:	/lisa/index.html
VR:	/lisa/index.html?version=1203987150
VHR:	/lisa/index.html?version=version-history

That would mean we must use URLs like:
VCR:	/lisa/index.html now
VR:	/__versions/lisa/index.html__1203987150
VHR:	/__vh/lisa/index.html

The draft ought to state clearly whether parameterized URLs are
acceptable or not as URLs for VRs, VHRs.  IMHO, it would be perfectly
fine to use parameterized URLs to refer to versions and VHRs.  Yes, it's
ugly, but it's less ugly than the alternative.

(BTW, he second class of URLs above is clearly only suitable for
automated access in some fashion, not by somebody typing in the URL.  I
can't think of a good way to make them prettier without using up
valuable URLs that users might want for other purposes.  I know I've
covered this in earlier mails, but I'll repeat: I'm unhappy with that,
it would be nasty to force all implementations to have rather ugly URLs,
by the combination of requiring non-reusable version URLs and not
allowing parameterized URLs.  Failing changes along those lines, does
somebody have a better legal suggestion for pretty URLs?)

2) Versioning of Properties

We need a kind of property that applies to all versions, or to put
another way, properties that apply to the version-controlled resource
itself.  For example, the "owner" property maybe ought to apply to the
whole shebang:  when you change the owner, the new owner has to be
responsible for everything, from the first version to the last and
including the version-controlled resource and version history.

Other properties might change every day, and we don't necessarily want
to create a new version of the document (a copy of the body??!!) every
time that property changes.  One way of dealing with this is to make the
frequently-changed properties apply to the VCR.

This doesn't seem possible with the current draft, because PROPFIND and
PROPPATCH methods applied to the VCR's URL are interpreted with respect
to the default version.  This is related to "passthrough" issue which
I'll bring up in another email.

3) Definiton of Version History Resource

The draft states 'A "version history" is a resource that contains all
the versions of a particular version-controlled resource.'

 - What does 'contains' mean?
 - How does this mesh with later implications, that there can be more
than one version history resource for a VCR?  This may be a
misunderstanding however please clarify.


4) The existence of version history resources

Section 2.1.1 "In core versioning, a version is exposed as an HTTP
resource with a server-defined URL, but a version history is exposed as
an HTTP resource only when the server supports the version-history
option (see Section 5)."

Section 2.4: "If the request-URL identifies a versionable resource, a
new version history resource is created."

Do core versioning servers need to create VHRs and not expose them, or
not create them at all?  Please clarify that core need not create new
version history resources at all :)


5) Definitions of precursor-set and predecessor-set

These definitions are circular.  The predecessor set is defined as
containing the set of predecessors.  This does not define what a
predecessor is, or how it is different from a precursor (aren't they
more or less synonyms?).  Also, what's the meaning of these on the VCR,
vs the same properties on the version?  Why do you need these properties
on a VCR when they're already on the version?
(Do these belong in CORE at all?)

6) DAV:version

I think somebody already pointed out that the DAV:version property was
redundant since it only contained the URL for the version it was on...

7) How do you distinguish between:
 - A versionable resource
 - A non-versionable resource
 - A version-controlled resource

Let's say the client wishes to present a simple UI which lists all the
resources in a collection, and can tell what each resource is, allowing
operations like "show me the version history" or "turn versioning on" to
be available only when appropriate.  How, exactly, is this accomplished?
What property is retrieved?

8) Clarify status reporting functionality early

The document uses the headers "Postconditions" and shows strings like
"DAV:put-under-version-control", throughout the document.  However, the
way status reporting is handled is only explained very late in the
document.  Please explain this early on.

Also the draft MUST define for each response string, what numerical HTTP
response code MUST be used in the response header.  Don't leave this up
to variation among implementations.

9) What is DAV:checkout-response

The definition of the "DAV:already-under-version-control" status message
(er, I mean 'postcondition') uses the "DAV:checkout-response" element.
That's not part of core.

10) Interactions between LOCK and VERSION-CONTROL

State whether a locked resource can be placed under version-control, and
whether the lock-token must be supplied with the VERSION-CONTROL method.

11) Interaction between existing headers and new methods

What happens when Depth is applied to the VERSION-CONTROL method?  It
seems that this is being addressed in a mail thread, but the
specification must define the behaviour.  What exactly happens if
anything in the scope can't be turned into a VCR?

Or Depth and the REPORT method?  Is Overwrite header ignored on REPORT?
FOrbidden?

What about existing HTTP headers such as Chunked-encoding and MD5?  Do
any of them apply?  Are they ignored? Forbidden?

12) Version-tree report

In 2.5, the version-tree report is required to be a "DAV:multistatus".
The response could for that could reasonably be 200 Success or 207
multistatus.  Your example shows 200.  Please state normatively, which
response code is required.

13) Root versions

In 2.9, the root version of a version history "must not be deleted".
Why is that?  This seems like an implementation issue, not a
protocol/interoperability issue.  Please leave this issue up to the
implementation to decide whether or not to allow deletion of old
versions, and how to deal with any subsequent rearrangements that might
be necessary.

14) (DAV:initialize-precursor)

"(DAV:initialize-precursor): If the source of the COPY was a version and
if the destination of the COPY supports the DAV:precursor-set property,
the DAV:precursor-set of the destination MUST identify that version.  If
the source of the COPY was a version-controlled resource, the
DAV:precursor-set MUST identify the DAV:checked-in or DAV:checked-out
version of that resource."

We don't understand this paragraph at all.  We don't know what a
precursor is, or what to identify, or what this is doing in CORE.
Please move this entirely out of CORE.

15) Version-history-is-tree

"(DAV:version-history-is-tree): If the request-URL identifies a
version-controlled resource that was automatically checked out because
DAV:auto-version was DAV:when-locked, then the versions identified by
the DAV:predecessor-set of the checked-out resource MUST be descendants
of the root version of the version history for the DAV:checked-out
version."

What does locking have to do with whether the versions must be
descendants of the root version?  Wouldn't this also apply when doing
autoversioning when unlocked?  We don't really understand this
paragraph.  Again, we wonder what this is doing in core.

16) New definition of Overwrite

Please clarify the new definition of Overwrite.

If you COPY directory 'mydir' with 'mydir/foo' and 'mydir/bar' to a
directory elsewhere with 'mydir/baz', do you end up with a directory at
the destination with TWO children, or THREE children?  In other words,
do resources at the destination which do not overlap resources from the
source get deleted?

I prefer 'no', btw.

17) OPTIONS supported-method-set

Section 23.6:  this defines 'supported-method-set', but in fact there's
already a header that expresses this.  How are you dealing with that
redundancy?


Lisa
Received on Thursday, 1 February 2001 23:22:48 GMT

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