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Re: WebDAV/DeltaV Interoperability and XML Validation

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Sun, 4 Feb 2001 15:42:15 -0500 (EST)
Message-Id: <200102042042.PAA19553@tantalum.atria.com>
To: ietf-dav-versioning@w3.org

Rather than define a variant of the WebDAV XML, and negotiate
for different variant of the XML with the Content-Type header,
wouldn't it be much simpler just to allow property tags to be empty
in the DTD?

Cheers,
Geoff

   Date: Sun, 04 Feb 2001 02:56:27 +0000
   From: "James J. Hunt" <jjh@allerton.de>

   Dear Colleagues,

   After much thought, we have finally devised a way to provide for XML
   validation in DeltaV without breaking existing WebDAV clients.  There
   are only two points where the DTD given in WebDAV is not validatable:=20
   property tags occur both as empty-element tags and as begin/end tag
   pairs, and though the DTD is named webdav-1.0, it gives no definition
   for that tag.   Two small changes would make the DTD usable.

   The problem is that to do this, an incompatibility would be introduced
   between current implementations and ones based on the new DTD.  The
   solution to this problem is to define a full validatable DTD for DeltaV
   including the modifications to webdav,then provide for two modes of
   operation.

   Since a server can only react to a client request, it can send a
   response in the correct mode based on the HTTP header sent by the
   client.  A server MUST send an old style WebDAV response if the option
   "valid=3Dtrue" is not listed in the Content-Type header entry.  =
   However,
   if the media type contains "valid=3Dtrue" as follows, the server MUST =
   send
   valid XML:

       Content-Type: application/xml; charset=3D"utf-8"; valid=3Dtrue

   The presence of the valid=3Dtrue option means that the XML being sent =
   is
   valid, but it does not mean that the receiver must check that validity. =

   Validation is done at the receivers discretion.  Note, that application
   is used here instead of text. Though WebDAV specifies either text or
   application, text is not really appropriate, because text is meant for
   documents designed for display to a user.  Here, XML is intended for
   information exchange between programs.

   A client must ask the server if it supports valid XML.  If a server
   returns a DAV responseheader containing version-control, then the =
   server
   MUST support valid XML.  The client can then send the appropriate XML
   message.  Non valid XML messages are limited to those used by WebDAV.

   These rules insure that all old clients will work with new
   version-control servers and all new client will work with old WebDAV
   servers.  Since the changes to the WebDAV part of the protocol are
   small, supporting both forms of WebDAV messages is not much of a burden
   on either clients or servers. The use of valid XML is then an extension
   to WebDAV, that is introduced by DeltaV.  WebDAV could use the same
   method to add valid-xml as a general option in its next draft.

   Sincerely,
   James J. Hunt
   J=FCrgen Reuter
Received on Sunday, 4 February 2001 15:43:14 GMT

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