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Proposal: Wildcards for WSDL 1.2

From: David Orchard <dorchard@bea.com>
Date: Wed, 16 Jul 2003 13:34:29 -0700
To: <www-ws-desc@w3.org>
Message-ID: <010601c34bd9$a8f15300$620ba8c0@beasys.com>
I'd like to propose the use of wildcards in WSDL 1.2 rather than
substitution groups.  My understanding of the rationale for substitution
groups is at least two-fold: Problems with determinism, and desire for
validation.  On the first reason, there are some schema techniques that can
be used that allow full extensibility and backwards/forwards compatible
changes.  The validation requirement I've addressed separately.

The core technique is to make the extensions in the same namespace into an
optional extension element.  The documented type then becomes:

  <xs:complexType name="ExtensibleDocumented" abstract="true" mixed="false">
  <xs:annotation>
  <xs:documentation>This type is extended by component types to allow
attributes from other namespaces to be added.</xs:documentation> 
  </xs:annotation>
  <xs:complexContent>
  <xs:extension base="wsdl:Documented">
  <xs:anyAttribute namespace="##any" processContents="lax" /> 
  <xs:element name="Extension" type="wsdl:ExtensionType" minOccurs="0"
maxOccurs="1"/> 
  <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded"
namespace="##other"/> 
  </xs:extension>
  </xs:complexContent>
  </xs:complexType>

  <xs:complexType name="ExtensionType">
   <xs:sequence>
      <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded"
namespace="##targetnamespace"/>
   </xs:sequence>
   <xs:anyAttribute/>
  </xs:complexType> 

This might not quite be it, because the wsdl:required attribute needs to be
applicable to same namespace and different namespace extensions.

This resolves the determinism problems with namespace="##any" which can't
follow elements with minOccurs!=maxOccurs.  It makes the tree a bit more
complicated when forward compatible schema changes happen in the same
namespace, as the extensionType needs to be refined for each extension.  As
in, adding a <wsdl:foo/> in a forwards compatible way means that the
instance looks like <Extension><foo/></Extension>.  But this does allow
forwards and backwards compatible changes.

What do y'all think?

Cheers,
Dave

> -----Original Message-----
> From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org]On
> Behalf Of Jonathan Marsh
> Sent: Wednesday, June 18, 2003 7:48 AM
> To: www-ws-desc@w3.org
> Subject: Examples of substitution group extending WSDL.
> 
> 
> 
> Results of my tinkering below.
> 
> First, I created an instance with a brand new extension to see how a
> fresh extension schema would work.
>  
>   <definitions xmlns="http://www.w3.org/@@@@/@@/wsdl"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xmlns:my="http://www.example.com/extensions/mine"
>  
> xsi:schemaLocation="http://www.example.com/extensions/mine 
> extension.xsd
> http://www.w3.org/@@@@/@@/wsdl wsdl.xsd"
>                targetNamespace="http://example.com/jonathan/test">
>     <documentation>This file tests validation of an extended WSDL
> document</documentation>
>     <my:extension>Jonathan Marsh</my:extension>
>   </definitions>
> 
> I described this extension with a schema, and inserted it into the
> globalExt substitution group (which allows the extension to appear at
> the top level, and almost anywhere else, within WSDL).
> 
>   <xs:schema targetNamespace="http://www.example.com/extensions/mine"
>              xmlns:wsdl="http://www.w3.org/@@@@/@@/wsdl"
>              xmlns:xs="http://www.w3.org/2001/XMLSchema"
>              elementFormDefault="qualified">
>     <xs:import namespace="http://www.w3.org/@@@@/@@/wsdl"
>                schemaLocation="wsdl.xsd"/>
>     <xs:element name="extension" type="xs:string"
>                 substitutionGroup="wsdl:globalExt"/>
>   </xs:schema>
> 
> Notes:
> 1) The extension schema imports the wsdl schema for the purpose of 
>    allowing the substitution group to be specified.
> 2) The validator needs to associate both the extension schema and 
>    the WSDL schema.  In this case I used the xsi:schemaLocation 
>    mechanism.
> 
> 
> Next I took an existing vocabulary (DSig) and tried to embed it in the
> WSDL.
> 
>   <definitions xmlns="http://www.w3.org/@@@@/@@/wsdl"
>                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>                xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
>                xsi:schemaLocation="http://www.w3.org/2000/09/xmldsig#
> wsdl+dsig.xsd http://www.w3.org/@@@@/@@/wsdl wsdl.xsd"
>                targetNamespace="http://example.com/jonathan/test">
>     <documentation>This file tests validation of an extended WSDL
> document</documentation>
>     <ds:Signature>
>       <ds:SignedInfo>
>         <ds:CanonicalizationMethod
> Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
>         <ds:SignatureMethod
> Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/>
>         <ds:Reference
> URI="http://www.w3.org/TR/2000/REC-xhtml1-20000126/">
>           <ds:Transforms>
>             <ds:Transform
> Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315"/>
>           </ds:Transforms>
>           <ds:DigestMethod
> Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
>           
> <ds:DigestValue>j6lwx3rvEPO0vKtMup4NbeVu8nk=</ds:DigestValue>
>         </ds:Reference>
>       </ds:SignedInfo>
>       <ds:SignatureValue>MC0CFFrVLtRlk=...</ds:SignatureValue>
>     </ds:Signature>
>   </definitions>
> 
> In order to validate this, I had to modify the DSig schema
> (wsdl+dsig.xsd) in three ways:
> 1) Add an appropriate substitutionGroup attribute, with the value of a
> WSDL extension group QName.
> 2) Declare WSDL namespace prefix so the QName is valid.
> 3) Add an import of the wsdl schema so the QName reference is 
> complete.
> 
> (new lines marked with "|")
> 
>   <schema targetNamespace="http://www.w3.org/2000/09/xmldsig#"
>           ...>
> |   <import namespace="http://www.w3.org/@@@@/@@/wsdl"
> |           schemaLocation="wsdl.xsd"/>
>     <element name="Signature" type="ds:SignatureType"
> |            substitutionGroup="wsdl:globalExt"
> |            xmlns:wsdl="http://www.w3.org/@@@@/@@/wsdl"/>
>     ...
>   </schema> 
> 
> Then I attempted the holy grail, a simple wrapper schema that 
> would have
> the effect of the schema above, while importing the DSig 
> schema without
> modification.  I failed in this because:
> - Element declarations in an imported schema cannot be overridden.
> - Redefine does not work on element declarations.
> - There is no other way to add elements to a substitution group.
> 
> I rejected modifications to the instance document that would enable a
> wrapper schema:
> - Changing the namespace of the top level element.
> - Introducing a wrapper element.
> 
> My conclusion is that the cleanest way to enable this scenario was
> copying and modifying the DSig schema with the simple additions found
> above.  I also note that this would be necessary to allow 
> wsdl:required
> attributes to appear on ds:Signature elements.
> 
> Do we find this limitation acceptable?  Does this limitation outweigh
> the benefits of our substitution group extensibility mechanism?
> 
> 
> 


Received on Wednesday, 16 July 2003 16:35:14 GMT

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