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Re: XML Schema requires a type in addition to name to identify an element

From: Amelia A Lewis <alewis@tibco.com>
Date: Thu, 31 Aug 2006 15:10:18 -0400
To: "Jonathan Marsh" <jmarsh@microsoft.com>
Cc: matthew@stickledown.com, www-ws-desc@w3.org
Message-Id: <20060831151018.f5b95093.alewis@tibco.com>

I have something of an objection to this issue.

WSDL can't constrain xsi:type.  *shrug*  Neither can W3C XML Schema.  It's sort of the point of xsi:type.  You get to have fun messing things up, by specifying High Weirdness where whitebread schematypes are expected.  Great way to break applications, btw.

I hope that at least the issue is expressed as "WSDL does not constrain the contents of the xsi:type attribute," because I think that this is more accurate than the submitted subject line (with respect to the submitter; the fact that the industry has to stand on its head and hold its jaw in odd positions in order to make W3C XML Schema meet requirements is *not* in fact something that should necessarily force WSDL to specify how to override or constrain those contortions).

Amy!
On Thu, 31 Aug 2006 11:28:44 -0700
"Jonathan Marsh" <jmarsh@microsoft.com> wrote:

>FYI, I've added this to the issues list as CR078
>[http://www.w3.org/2002/ws/desc/5/cr-issues/issues.html#CR078].
>
> 
>
>________________________________
>
>From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org] On
>Behalf Of Matthew Rawlings
>Sent: Thursday, August 31, 2006 11:04 AM
>To: www-ws-desc@w3.org
>Subject: RE: XML Schema requires a type in addition to name to identify
>an element
>
> 
>
>I confirm that you now understand this correctly.  
>
> 
>
>I agree with you that the existing industry standard XML Schema
>schemata are poorly adapted to being used in a WSDL service. This is
>to be expected as XML Schema predated WSDL.
>
> 
>
>I disagree that "one was stuck using a flexible schema (for political
>reasons)". My personal opinion is the reason is that current industry
>standard XML Schema schemata have long histories and large installed
>bases of standards-compliant schema. The choice is whether to adapt
>WSDL to XML Schema or adapt existing XML Schema schemata to WSDL. Both
>are possible, one is more costly than the other.
>
> 
>
>My personal opinion is it would be far better if people could be
>convinced for good engineering reasons. My personal opinion is that on
>an engineering basis the type of the element is more important than its
>name when dealing with a type system such as XML Schema provides. 
>
> 
>
>My personal opinion is a clear statement (positive or negative), from
>the W3C WSDL Working Group on the merits of using xsi:type in the root
>element would help industry standards groups prepare to adopt WSDL 2.0.
>Please make a statement to guide designers of XML Schema schemata in
>their adoption of WSDL.
>
> 
>
>Matthew Rawlings
>
>________________________________
>
>From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org] On
>Behalf Of Jonathan Marsh
>Sent: 31 August 2006 17:17
>To: matthew.d.rawlings@jpmchase.com; www-ws-desc@w3.org
>Cc: stabet@ruleml.org; Steve Ross-Talbot; ylafon@w3.org
>Subject: RE: XML Schema requires a type in addition to name to identify
>an element
>
> 
>
>Thanks for the complete example, I understand the scenario as far as
>the schema goes, but I'm not sure what you want added to WSDL to
>support this use case.
>
> 
>
>One way to interpret your proposal is that wsdl:input/@type constrains
>the allowed values of the xsi:type attribute appearing in the message
>instance.  In other words, the message must match both the element name
>defined by wsdl:input/@element, and have an xsi:type attribute with the
>value given by wsdl:input/@type (and structure corresponding to it).
>
> 
>
>The schema you provide allows the transport element to take on a
>variety of structures within the same element name.  In my experience
>this is so the client (or generator) of the data has flexibility.  The
>receiver is informed of the client's structural choice using xsi:type.
>
> 
>
>In WSDL, the schema defines the schema types deemed acceptable by the
>service.  If a WSDL specified a flexible schema such as the one below,
>one would expect it to be delegating the choice of structure to the
>client.
>
> 
>
>Yet in your scenario, this delegated flexibility then is constrained.
>The WSDL defines a flexible schema, and then takes this flexibility
>away by only allowing a specific xsi:type value.  One would presumably
>only need this capability because one was stuck using a flexible
>schema (for political reasons) that was poorly adapted to a
>WSDL-described service, which isn't a very compelling scenario.  If
>you really need and expect flexible structures, I would generally
>expect the WSDL to simply declare element=#any.
>
> 
>
>Please feel free to correct any misconceptions above, especially if
>I've misinterpreted your proposal in some way.  I'm just trying to
>understand better so we can resolve this quickly!
>
>


-- 
Amelia A. Lewis
Senior Architect
TIBCO/Extensibility, Inc.
alewis@tibco.com
Received on Thursday, 31 August 2006 19:14:42 GMT

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