Resctriction problem on complexType

Hi,

I have an error wuth the following schema using a restriction of a complexType.

The schema is not valid using different tools (SQC, XSDValid, Xerces, XmlSpy)...
But the error messages are not really understandable.

The aim is ti defne a restricted type by setting minOccurs to 1 to included choices.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
 <xs:complexType name="essai">
      <xs:choice>
           <xs:choice minOccurs="0" maxOccurs="unbounded">
                <xs:element ref="art1"/>
                <xs:element ref="art2"/>
           </xs:choice>
           <xs:choice minOccurs="0">
                <xs:element ref="s1" maxOccurs="unbounded"/>
                <xs:element ref="s2" maxOccurs="unbounded"/>
           </xs:choice>
      </xs:choice>
 </xs:complexType>

 <xs:complexType name="essaiRestrict">
      <xs:complexContent>
           <xs:restriction base="essai">
                <xs:choice>
                     <xs:choice maxOccurs="unbounded">
                          <xs:element ref="art1"/>
                          <xs:element ref="art2"/>
                 </xs:choice>
                 <xs:choice>
                          <xs:element ref="s1" maxOccurs="unbounded"/>
                      <xs:element ref="s2" maxOccurs="unbounded"/>
                 </xs:choice>
             </xs:choice>
        </xs:restriction>
      </xs:complexContent>
 </xs:complexType>
 
<xs:element name="art1"/>
 <xs:element name="art2"/>
 <xs:element name="s1"/>
 <xs:element name="s2"/>
 
</xs:schema>

Can anybody explain the problem ?

Thanks in advance

-- 
Bruno Chatel
Tel : (+33) (0)4 96 11 14 57
bcha@chadocs.com
http://www.chadocs.com
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