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Resource class

From: <Tim_Ellison@uk.ibm.com>
Date: Fri, 11 May 2001 22:59:39 +0100
To: ietf-dav-versioning@w3.org
Message-ID: <80256A49.0078D6CB.00@d06mta07.portsmouth.uk.ibm.com>


[I did send this mail once, but it hasn't appeared, so here's attempt #2]
---------------------------
The issue of determining a versioning resource's classification based on
the absence (or otherwise) of properties has been raised before on the
list.  Recently however, (in other contexts) people have shifted in favour
of extensions to <DAV:resourcetype> to convey more 'type' information.

In support of this shift of opinion, here's my renditioning of how a client
currently determines the resource classification (if, for example, if a
client were given a URL in a property with no other information) in a
versioning world.

To get an accurate classification the client has to issue a PROPFIND then
look at the results as follows (hopefully my layout is not too cryptic):

>>REQUEST
     PROPFIND /foo HTTP/1.1
     Host: bar.com
     Content-Type: text/xml; charset="utf-8"
     Content-Length: xxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D="DAV:">
         <D:prop>
             <D:resourcetype/>
             <D:auto-checkout/>
             <D:checked-in/>
             <D:checked-out/>
             <D:version-name/>
             <D:workspace-checkout-set/>
             <D:baseline-controlled-collection/>
             <D:subactivity-set/>
         </D:prop>
     </D:propfind>

Interpreting the results
--------------
Key: The major classifications are listed below from (1) to (8).

Each entry marked with a plus-sign can exist in a checked-in xor
checked-out state.
+
 <DAV:checked-in> defined -- the resource is checked-in.
 <DAV:checked-out> defined -- the resource is checked-out.

Each entry marked with an astrix can exist as a collection resource xor a
non-collection resource.
*
 <DAV:resourcetype> value is not <DAV:collection/> -- the resource is not a
collection.
 <DAV:resourcetype> value is <DAV:collection/> -- the resource is a
collection.


(1+*) Version-controlled resource.
     <DAV:auto-checkout> defined

(2*) Version.
     <DAV:version-name> defined

(3) Version history.
     <DAV:resourcetype> value is <DAV:version-history/>

(4) Workspace.
     <DAV:resourcetype> value is <DAV:collection/>
     <DAV:workspace-checkout-set> defined

(5*) Working resource.
     <DAV:checked-out> defined
     <DAV:auto-checkout> *not* defined

(6+) Version-controlled configuration.
     <DAV:baseline-controlled-collection/> defined

(7) Baseline.
     <DAV:resourcetype> value is <DAV:baseline/>

(8) Activity.
     <DAV:subactivity-set> defined.


Observations
----------
(i) For the most part we only care if a property is defined - i.e., it
exists, and not what it's value is.  There is currently no way to ask this
question in WebDAV.

(ii) It would seem that activities should have a <DAV:resourcetype> of
<DAV:activity>, but I didn't see that in the -15 spec.

(iii) The only way I could see to distinguish a workspace from a 'regular'
collection was the presence of <DAV:workspace-checkout-set/> which it would
seem is likely a very expensive property to query.


Conclusions
---------
(a) We should extend <DAV:resourcetype> to provide all this classification
information in a single property.
(b) How about extending <DAV:propname/>? such as
<DAV:propname>
    <DAV:checked-out/>
</DAV:propname>
then the client would get back just the name or a 404 to determine if it
exists.


Tim
Received on Friday, 11 May 2001 18:00:35 GMT

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