Data model task force recommends adoption of data model formulation

On Friday Sept. 12th, the data model task force held a teleconference
during which we considered the draft reformulation [1]* of MTOM based on
the new XPath XQuery data model [2].  During the call, the task force
unanimously agreed on the following recommendations to the XML Protocols
Workgroup:

* The draft at [1] is ready for consideration by the entire XML Protocols
Workgroup.

* The DM formulation, as presented in [1], should be adopted as the basis
for future work on MTOM (though this is an initial draft and will require
cleanup and editing).

It should be noted that only three members of the task force were present
for the call on the 12th, and while the above is their unanimous agreement,
previous calls have had broader attendance.

The task force also considered concerns raised by Ugo Corda at [3], and
decided that the response at [4] represents the consensus of the task
force.  In quick outline, Ugo's concern is that, in the interests of
sticking to the established scope of the existing MTOM design, and
specifically in allowing MTOM messages to be sent through the existing SOAP
HTTP binding, the data model formulation is presented as lossy.  Although
type information from the data model is used as a hint by bindings to
optimize SOAP transmission, such type information is not in general
transmitted.  I believe Ugo's concern is that if the data model is used
all, it should be transmitted faithfully.  This concern presents a Catch-22
for those interested in the data model formulation:  the XMLP WG has
already agreed, at least tentatively, that regardless of how the
specification is modeled, type information is not necessarily to be
transmitted.  The task force believes that on balance, the benefits of
using terminology that is on its way to Recommendation status, and indeed
doing so in way that might provide a basis for future specifications that
would indeed transmit the full data model faithfully, outweigh any
negatives resulting from the lossy use of the model in MTOM at this time.

Thus, we recommend consideration and adoption of the draft at [1] as the
basis for future work on MTOM.

At least one set of details remains to be resolved if the DM formulation is
to be used: the current draft does not discuss all of the accessors
provided by the data model.  For example, element nodes [5] provide a
base-uri [6], which in principle can vary for each element.  Future
versions of the draft would need to explain that, like type information,
such base URI and similar information is not transmitted.  This limitation
is consistent with the general philosophy that MTOM will transform the
input data model to a different (but predictably different) output data
model at the receiver.  In general, the transmission will exactly preserve
certain information, will lose other information such as base URI and type,
and will not add or synthesize other information, except as directly
follows from the losses (e.g. typed values change in the obvious way when
type information is lost.)

Thank you very much.

Noah

* The draft linked from [1] is incorrectly formatted as a full WD.  The
current copies at [7,8] correctly show editors' copy status, but are
otherwise identical.  I referred to [1] im the note above, as it has the
original submission text to the WG.

[1] http://lists.w3.org/Archives/Public/xml-dist-app/2003Aug/0014.html
[2] http://www.w3.org/TR/xpath-datamodel/
[3] http://lists.w3.org/Archives/Public/xml-dist-app/2003Aug/0018.html
[4] http://lists.w3.org/Archives/Public/xml-dist-app/2003Sep/0007.html
[5] http://www.w3.org/TR/xpath-datamodel/#ElementNode
[6] http://www.w3.org/TR/xpath-datamodel/#dm-base-uri
[7]
http://www.w3.org/2000/xp/Group/3/06/Attachments/OptimizationMechanismDM.xml
[8]
http://www.w3.org/2000/xp/Group/3/06/Attachments/OptimizationMechanismDM.html




------------------------------------------------------------------
Noah Mendelsohn                              Voice: 1-617-693-4036
IBM Corporation                                Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
------------------------------------------------------------------

Received on Saturday, 13 September 2003 10:48:53 UTC