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RE: LC124: Ignore Unknowns, some proposed text

From: Jonathan Marsh <jmarsh@microsoft.com>
Date: Wed, 15 Jun 2005 12:57:25 -0700
Message-ID: <7DA77BF2392448449D094BCEF67569A507E85683@RED-MSG-30.redmond.corp.microsoft.com>
To: <paul.downey@bt.com>, <dorchard@bea.com>
Cc: <www-ws-desc@w3.org>

Would this be a valid schema that accommodates both the original and the
extended structure?

  <xs:complexType>
    <xs:sequence>
      <xs:element name="first"/>
      <xs:element name="last" maxOccurs="unbounded">
        <xs:complexType>
          <xs:attribute name="role" type="xs:token" use="optional"
default="primary"/>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>

> -----Original Message-----
> From: paul.downey@bt.com [mailto:paul.downey@bt.com]
> Sent: Wednesday, June 15, 2005 12:44 PM
> To: Jonathan Marsh; Jonathan Marsh; dorchard@bea.com
> Cc: www-ws-desc@w3.org
> Subject: RE: LC124: Ignore Unknowns, some proposed text
> 
> Jonathan wrote:
> 
> > Isn't one of the advantages of Henry's mechanism is that it the
> > results
> > are predictable and therefore interoperable?  For instance, given a
> > schema for the structure:
> >
> >   <name>
> >     <first/>
> >     <last/>
> >   </name>
> >
> > And a message instance of:
> >
> >   <name>
> >     <first/>
> >     <last/>
> >     <last role="alternate-spelling"/>
> >   </name>
> >
> > Henry's algorithm should predictably trim one (the last I think)
> > <last/>
> > element.  I can imagine a reasonable algorithm that trims the first.
> 
> That's a good point and does nicely expose a hole in my text.
> 
> There's an anticipation (on my part) that the additional content will
> be sent as a result of a backwards compatible change in the schema.
> 
> In this example, the v2 schema that accepts and processes both
> the v1 and v2 messages, but with the optional additional 'last'
> in the middle  would have to look something like:
> 
>     <xs:complexType name="nameType">
>         <xs:sequence>
>             <xs:element name="first" />
>             <xs:element name="last" minOccurs="0" />
>             <xs:element name="last" />
>         </xs:sequence>
>     </xs:complexType>
> 
> or:
> 
>     <xs:complexType name="nameType">
>         <xs:sequence>
>             <xs:element name="first" />
>             <xs:any />
>             <xs:element name="last" />
>         </xs:sequence>
>     </xs:complexType>
> 
> or:
> 
>     <xs:complexType name="nameType">
>         <xs:all>
>             <xs:element name="first" />
>             <xs:element name="last" maxOccurs="2" />
>         </xs:sequence>
>     </xs:all>
> 
> I suspect writing a v2 schema in which the unexpected
> element appears ahead of the expected element with the same name
> is not possible in XML Schema 1.0 without breaking UPA.
> All of the above are invalid Schema 1.0 examples.
>
> > Which actually brings forth another question:  The schema is
> primarily
> > used for code generation, and for mapping the data to that code.
> > Given
> > the above example, which <last/> will be mapped to code?  Especially
> > if the following is also allowed:
> >
> >   <name>
> >     <first/>
> >     <last role="alternate-spelling"/>
> >     <last/>
> >   </name>
> >
> 
> Once again, I can't see how to write the v2 schema for this example,
> apart
> from making role optional (and ignored) on the v1 'last' element and
> having
> the second 'last' being optional.
> 
> > Do we need Henry's algorithm in play for extracting data from the
> > message, as well as for the optional validation step?  That would
> > introduce a mandatory validation step in all messages, which could
> be
> > undesirable.
> 
> That would be undesirable, hence my wanting to prescribe how unknowns
> can be easily ignored by a 'ignoreUnknowns' aware processor.
> 
> I am wondering how much would have to be added to my proposed
> text to become precise, and would that precision just become another
> way of wording Henry's technique.
> 
> One way forward could be to add a line requiring there to be a
> compatible
> schema which represents both the v1 and v2 messages. I'll think some
> more
> on this ahead of tomorrow's call.
> 
> Paul
Received on Wednesday, 15 June 2005 19:57:51 GMT

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