Re: Target-Selector

Geoffrey M. Clemm (geoffrey.clemm@rational.com)
Wed, 22 Dec 1999 13:22:55 -0500 

Date: Wed, 22 Dec 1999 13:22:55 -0500
Message-Id: <9912221822.AA08687@tantalum>
From: "Geoffrey M. Clemm" <geoffrey.clemm@rational.com>
To: ietf-dav-versioning@w3.org
In-Reply-To: <1999Dec22.104500.1250.1425599@otismtp.ott.oti.com>
Subject: Re: Target-Selector


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