I think you can change this to the following and get what you want:

 <xs:choice>
 <xs:sequence>
   <xs:element name="a" type="xs:string"/>
   <xs:element name="b" type="xs:string" minOccurs="0"/>
 </xs:sequence>
 <xs:element name="b" type="xs:string"/>
 </xs:choice>

The strategy works for simple cases like this, but doesn't extend well to=
 
having more elements that have to share the same sort of occurrence 
constraints.  This is an area that future schema recommendations are look=
ing 
at.

HTH,

Pete.
--
==========================
====================
Pete Cordell
Codalogic Ltd
for XML Schema to C++ data binding visit
 http://www.codalogic.com/lmx/
==========================
====================

----- Original Message ----- 
From: "Markus Gamperl" <markus.gamperl@g...>
To: <xmlschema-dev@w...>
Sent: Wednesday, June 27, 2007 8:21 PM
Subject: xs:choice question


>
> Hello!
>
> I have the following xml fragment example:
>
> <data>
> <a>a test</a>
> <b>b test</a>
> <data>
>
> the schema should check the following rules (three options):
> - element a must exist, b may not
> - element b must exist, a may not
> - element a and b must exist
>
> Therefor I have defined the following choice:
> ...
> <xs:choice>
> <xs:element name="a" type="xs:string"/>
> <xs:element name="b" type="xs:string"/>
> <xs:sequence>
>   <xs:element name="a" type="xs:string"/>
>   <xs:element name="b" type="xs:string"/>
> </xs:sequence>
> </xs:choice>
> ...
>
> The xml editor raises an error - something about non determenistic 
> declaration...
>
> Do you have a suggestion how to define these three rules?
>
> Thanks for your help!
> Markus
> -- 
> Psssst! Schon vom neuen GMX MultiMessenger geh=F6rt?
> Der kanns mit allen: http://www.gmx.net/de/go/multimessenger
>
> 



From tmrfcm@g... Fri Jun 29 18:38:37 2007
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