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LC124 - Support of evolution of messages described in Schema 1.0

From: <paul.downey@bt.com>
Date: Fri, 15 Jul 2005 17:56:36 +0100
Message-ID: <2B7789AAED12954AAD214AEAC13ACCEF2709E4E7@i2km02-ukbr.domain1.systemhost.net>
To: <www-ws-desc@w3.org>

Ahead of next week's F2F here's my best understanding of  the current state 
of proposals and discussion for LC124.
 
http://www.w3.org/2002/ws/desc/4/lc-issues/issues.html#LC124



** Description and Justification **

Original Proposal (Paul):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0012

In essence, there is no way to describe the common and natural
evolution of an XML structure using XML Schema 1.0, eg.:

v1:

  <customer>
	<firstName>Paul</firstName>
  </customer>

v2:

  <customer>
	<firstName>Paul</firstName>
	<lastName>Downey</lastName>
  </customer>

v3:

  <customer>
	<firstName>Paul</firstName>
	<lastName>Downey</lastName>
	<middleName>Sumner</middleName>
  </customer>

whereby a format may evolve remaining backwards compatible following
three simple rules:

	- make additional items optional
	- don't delete items
	- don't change the meaning of existing items




** Proposed Text **

Latest evolution (Jonathan):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0091

"""
The "ignoreUnknown" property set to "true" denotes that the service accepts without faulting additional _unexpected items_ in messages sent to that service.  _Unexpected items_ are attributes and elements not defined by the schema for a particular element in the input message.  _Unexpected items_ may appear in any namespace including the targetNamespace of a known schema, as well as in a namespace for which no schema is currently known.  _Unexpected items_ includes the descendents of the item, such any child elements, attributes and content.  

Note: one mechanism for accomplishing this is to validate a message after content that is not known has been removed.  The unknown content may be identified by a W3C XML Schema processor.  The [validity] property in the Post Schema-Validation Infoset will contain a "notKnown" value if unknown content is found.
"""

The same assertion, or a parallel one should denote that the service is liable to insert unexpected items in messages it emits which a client should accept.


resulting from text from DaveO:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0083

and Paul:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0036




** Proposed Syntax **

There is uniform agreement that a ignoreUnknown flag would be required to 
control this feature, true meaning ignoreUnknowns, false meaning strict validation
applies. 

Options for syntax:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0097.html



** Discussion **

Berlin F2F, 1 June 2005, overview of issue:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/att-0002/20050601-ws-desc-minutes.html#item11

Telcon 9 June 2005, agreed not to close with no action:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/att-0015/20050609-ws-desc-minutes.html#item06

Telcon 16 June 2005, validate twice and IP:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/att-0059/20050616-ws-desc-minutes.html#item09

W3C Workshop on XML Schema 1.0 User Experiences, 22 June 2005:
Slides (Paul):
http://www.w3.org/2005/06/22-schema-workshop/LC124/slides.html

Minutes:
http://www.w3.org/2005/06/22-xsd-user-minutes.html#item03

Chairs' summary report:
http://www.w3.org/2005/06/21-schema-workshop/chairs-report.html#Versioning

Telcon 23 June 2005, feedback from workshop:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/att-0085/20050623-ws-desc-minutes.html#item04

Telcon 30 June 2005, syntax, precedence of flag on types and endpoint:
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/att-0015/20050630-ws-desc-minutes.html#item04 



** Some Mailing List Concerns **

That unknowns might be ambiguous (Jonathan):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0039.html
 
You have to be able to write a schema which describes the V2
and V1 messages, UPA actually helps here (Paul):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jun/0055.html

Lack of formal text to cite (Arthur):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0026.html

Similar issues as with SOAP Encoding (Arthur):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0019.html

But you can still validate (Paul):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0057

psvi:notKnown != unknown (Arthur):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0044.html
Explanation (Sandy Gao):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0050.html

Problems with ignoreUnknows (soap Headers and body element) (Amy):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0007.html

Attempt at a reply (Paul):
http://lists.w3.org/Archives/Public/www-ws-desc/2005Jul/0009.html

Evolution is a narrow use-case (Arthur, Umit and Pete Hendry (Cape))
various emails, refuted by Paul :-)

--
Paul
Received on Friday, 15 July 2005 16:56:43 GMT

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