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WSDL WG request for adding multiple version extensibility into Schema 1.1

From: David Orchard <dorchard@bea.com>
Date: Fri, 13 Feb 2004 12:06:01 -0800
To: <www-ws-desc@w3.org>
Message-ID: <01c601c3f26c$ce3eae70$6501a8c0@beasys.com>

Hi all,

Here's proposed text to send to the XML Schema WG on issue of versioning.
Please let me know when you can.  I'd prefer to send this before the wsd wg
telcon on thursday.

Dear Schema WG,

On behalf of the WSDL WG I'm conveying a use case for versioning and
question about a solution and the intentions for Schema 1.1.

In discussions on Providing Compatible Schema Evolution [1], the broad
question of extensibility and versioning as a whole was examined. And there
are tricky problems and difficult choices for solutions. Another important
question to ask is what is the minimum necessary for success in versioning?
If one assumes that we do not need to insert elements in arbitrary places,
just at the end, and retaining compatibility, then there may be a simpler
solution that XML Schema 1.1 could do. Let us take a simple name example
through two iterations. The first iteration adds an optional "middle" name
at the end of the name. The second option adds an optional "suffix" at the
end of the extended name.  This looks like:

<name>
	<first>Dave</first>
	<last>Orchard</last>
</name>

<name>
	<first>Dave</first>
	<last>Orchard</last>
	<middle>Bryce</middle>
</name>

<name>
	<first>Dave</first>
	<last>Orchard</last>
	<middle>Bryce</middle>
	<suffix>II</suffix>
</name>
We want these 3 of these documents to be valid against the 3 schemas. It
seems that the simplest change would be to have a "low priority" wildcard as
mentioned in previous discussions. The schemas using this would be something
like:

<xs:complexType name="nameType">
	<xs:sequence>
		<xs:element name="first" type="xs:string" />
		<xs:element name="last" type="xs:string" minOccurs="0"/>
		<xs:any namespace="##any"/>
	</xs:sequence>
</xs:complexType>

<xs:complexType name="nameType">
	<xs:sequence>
		<xs:element name="first" type="xs:string" />
		<xs:element name="last" type="xs:string" minOccurs="0"/>
		<xs:element name="middle" type="xs:string" minOccurs="0"/>
		<xs:any namespace="##any"/>
	</xs:sequence>
</xs:complexType>

<xs:complexType name="nameType">
	<xs:sequence>
		<xs:element name="first" type="xs:string" />
		<xs:element name="last" type="xs:string" minOccurs="0"/>
		<xs:element name="middle" type="xs:string" minOccurs="0"/>
		<xs:element name="suffix" type="xs:string" minOccurs="0"/>
		<xs:any namespace="##any"/>
	</xs:sequence>
</xs:complexType>

It seems that a low priority wildcard is sufficient to enable an explicit
extensibility point that allows backwards and forwards compatible evolution
through multiple versions with extension at the end of the type definition
and extension in the same namespace. This isn't the fullest solution, as it
does not allow for default extensibility, nor extensibility in between
elements. But this appears significantly improved over current capabilities.

I'm not able to track the intricacies of the discussion, but it appears that
the Schema group is talking about this in the context of RQ-135, with a
proposal at [2], another proposal about 2nd class wildcards at [3], and a
fair amount of follow on discussion.  Again, I can't follow through the
intricacies of the discussion of the ilk of subsumption of lexical spaces
versus value spaces for redefinition, and why a validator needs to look up
the tree for subsumption.

We are interested in determining whether the Schema WG sees: this use case
as important for Schema 1.1, whether this use case will be solved in Schema
1.1, if low priority wildcards are a solution to this problem, and if
low-priority wildcards will be the Schema 1.1 solution.

On behalf of the WSDL WG,
Dave Orchard

[1]
http://www.pacificspirit.com/Authoring/Compatibility/ProvidingCompatibleSche
maEvolution.html
[2] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2004Feb/0028.html
[3] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2004Feb/0035.html
Received on Friday, 13 February 2004 15:05:27 UTC

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