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Handling errors in DAV:propertyupdate

From: <jamsden@us.ibm.com>
Date: Wed, 12 May 1999 21:29:09 -0400
To: w3c-dist-auth@w3.org
Message-ID: <85256770.0008586B.00@d54mta03.raleigh.ibm.com>

There has been some discussion on the WebDAV mailing list concerning the
handling of PROPPATCH errors. The current WebDAV spec says that either all the
propertyupdates in a PROPPATCH must succeed, or none of the updates are
performed. This is sometimes a little extreme as there are cases when best
effort updates are ok, especially in the case of live properties. In order to
accomplish best effort, the client must do a PROPPATCH, examine the errors that
are returned, and do another PROPPATCH to perform the updates that would have
been successful.

Another scenario involves copying resources across servers. This would very
useful for publishing a web site from a development server to a production
server as well as sharing and reusing resources. Copy has a propertybehavior
element that indicates what should happen to live properties that are candidates
to be copied. If the copy method is completely executed within a single server,
then there is no problem processing the method. However, if the copy is to go
across servers, then there must be some way to handle the copying of live
properties. One way to implement cross-server copies is to use a WebDAV to GET
the contents of the source resource and PUT those contents to the destination
resource. This would be followed by a PROPFIND to get the properties of the
source resource, and a PROPPATCH to create the properties of the destination.
However, as in the first scenario, there is no way for the server to indicate
what should be done with live properties on the source resource. The server
can't assume its live properties will be live for the destination, and there is
no way to query the destination resource to see what properties would be live.

Both of these scenarios and others could be supported if the DAV:propertyupdate
element was extended to include information similar to the DAV:propertybehavior
element. Then the client could specify how errors should be handled for each
property to be updated: ignore the error, or fail. The default if nothing was
specified would be to fail the update, and therefore the complete PROPPATCH.
This would be consistent with the current WebDAV spec.

I propose we extend the DAV:set and DAV:remove elements to include information
describing how the client wishes to handle errors. The DTD additions would be:

<!ELEMENT propertyupdate (remove | set)+>

<ELEMENT set (prop, updatebehavior?)>
<ELEMENT remove (prop, updatebehavior?)>

<!ELEMENT updatebehavior (ignore | mustsucceed)>
<!ELEMENT mustsucceed (#PCDATA | href+)>

If an updatebehavior is not included, it is equivalent to specifying
<mustsucceed>*</mustsucceed> meaning that all the updates must be successful or
none of them are performed. If a list of URIs is included as the value of
mustsucceed, then the named properties must be updated successfully. The #PCDATA
in element mustsucceed can only be "*" indicating all updates must be
successful. If ignore is specified, then the server must use best effort to
update the properties returning a multistatus indicating which properties were
not updated.

It would be possible to use propertybehavior instead of introducing a new
element updatebehavior as the semantics are the same. However, it might be
confusing as the words have different meaning.
Received on Wednesday, 12 May 1999 21:31:37 UTC

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