Re: Target-Selector

jamsden@us.ibm.com
Wed, 22 Dec 1999 14:55:24 -0500 

From: jamsden@us.ibm.com
To: ietf-dav-versioning@w3.org
Message-ID: <8525684F.0072E190.00@d54mta03.raleigh.ibm.com>
Date: Wed, 22 Dec 1999 14:55:24 -0500
Subject: RE: Target-Selector



How about sticking with separate headers as they are simpler and easier to
parse than one. I suggest headers that reflect the roles the values are
playing rather than their types. For example, Revision-Selector for the,
well, revision selector, and Override-Selector for the leaf if the revision
selector is being overridden. This is the same as Geoff's proposal, but it
keeps the notion of Workspace out of the Revision-Selector so we could
potentially use other things there like a label, configuration, revision
id, activity, etc.





Tim_Ellison@oti.com (Tim Ellison OTT)@w3.org on 12/22/99 02:06:36 PM

Sent by:  ietf-dav-versioning-request@w3.org


To:   ietf-dav-versioning@w3.org ('Delta V')
cc:

Subject:  RE: Target-Selector



I stand by my original proposal, although I agree we are only differing by
syntax.

Firstly, I would prefer not to have two headers simply because it promotes
header bloat (would that be Workspace:, Revision-Selector:,
Desination-Workspace: and Destination-Revision-Selector:?).

I find the name Target-Selector quite meaningful (as these things go :-)
and
a finally clause more intuative than recognising the overriding nature of
Revision-Selector/Workspace headers.

Secondly, using 'keyword-space-value' is, as you would say, morally
equivalent to a URI.  By specifying as URIs you have a natural forward
compatibility solution that you cannot otherwise guarantee.

.. and finally, having to specify "configuration" is redundant since the
server will have to ensure the following URL really is a configuration and
not another type.

So my objections are more on (relatively trivial) implementation grounds
than the semantics of our solution.

Tim
 ----------
From: Geoffrey M. Clemm
To: ietf-dav-versioning
Subject: Re: Target-Selector
Date: Wednesday, December 22, 1999 1:28PM

I'd like to propose a syntactic variant on Tim's proposal:

Instead of adding a "finally" clause to the Target-Selector header,
let's replace the "Target-Selector" header with a "Workspace" and a
"Revision-Selector" selector header.  One advantage is that
Workspace and Revision-Selector are more self-explanatory than
Target-Selector.

A Workspace header specifies either a Workspace URL or nothing,
where nothing corresponds to the old "metadata" Target-Selector.
A Revision-Selector specifies a label, an id, or a configuration.
A Workspace header specifies target selection for the entire request.
A Revision-Selector header overrides the Workspace header for the
versioned resource identified by the Request-URL.


workspace-hdr         = "Workspace" ":" [ URL ]
revision-selector-hdr = "Revision-Selector" ":" revision-selector
revision-selector     = "id" segment
                      | "label" segment
                      | "configuration" URL

I'd like to keep the "id", "label" and "configuration" keywords
to avoid ambiguity in case we decide to extend those namespaces.

Cheers,
Geoff

   From: Tim_Ellison@oti.com (Tim Ellison OTT)

   I'd like to propose a change to the Target-Selector as described in the
   protocol spec.

   Presently, the valid values are:
 workspace "<URI>"
 id "<revision id>"
 label "<label>"
 metadata

   The change would accomodate the situation where the client wants to
select
   collection revisions using a workspace, and the final resource using a
label

   or id.  Without such a change the "id" target selector is of little/no
use
   for selecting resources in collections (the collection will not have the
   same id as the "leaf" resource).

   The change would also allow the client to select a revision based
directly
   upon an activity and provides extensibility for other selection schemes.

   target selector = Target-Selector ":" URI [ LWS "; finally" URI ]

   The use of URIs gives us extensibility for defining new selection
   mechanisms, and the optional "finally" clause allows clients to specify
a

   different selector for the leaf.  (I don't see any benefit for N
selection
   methods.)

   Example URIs would be id:some_id, label:some_label, metadata:, and
   http://machine/resource where 'resource' is a workspace or activity or
   something else (the server gets to figure out which by looking at the
   resource type).  Specifying a resource that cannot be used for selection
   results in a bad request.

   Example target selectors would be:
     Target-Selector: http://foo.com/mywork
     Target-Selector: http://foo.com/mywork ; finally id:Rev12FP
     Target-Selector: label:bar ; finally http://foo.com/actif1

   Comments?
   Tim