Element occurence

I have following XML file:

<?xml version="1.0" encoding="UTF-8" ?>
<result xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation='schema.xsd'>
  <level4 id1='1'></level4>
  <level4 id1='2'></level4>
  <level4 id1='3'></level4>
  <level4 id1='4'></level4>
  <level5 id2='1'></level5>
  <level5 id2='2'></level5>
  <level5 id2='3'></level5>
  <level4 id1='1'></level4>
</result>

All elements under the <result> element should be optional, and they can 
occur multiple times.
In other words, the DTD representation of what I would like to accomplish is 
:

<!ELEMENT result ((level4?)*,(level5?)*,(level4?)*)>

I created following schema file:

<?xml version="1.0" encoding="UTF-8" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="qualified" >

  <xsd:element name="result" >
    <xsd:complexType mixed="false" >
      <xsd:sequence>
        <xsd:sequence minOccurs="0" maxOccurs="unbounded">
          <xsd:element name="level4" type="Type1" minOccurs="0"
maxOccurs="1" />
        </xsd:sequence>
        <xsd:sequence minOccurs="0" maxOccurs="unbounded">
          <xsd:element name="level5" type="Type2" minOccurs="0"
maxOccurs="1" />
        </xsd:sequence>
        <xsd:sequence minOccurs="0" maxOccurs="unbounded">
          <xsd:element name="level4" type="Type1" minOccurs="0"
maxOccurs="1" />
        </xsd:sequence>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <xsd:complexType name="Type2" mixed="false" >
    <xsd:attribute name="id2" >
      <xsd:simpleType>
        <xsd:restriction base="xsd:int" />
      </xsd:simpleType>
    </xsd:attribute>
  </xsd:complexType>

  <xsd:complexType name="Type1" mixed="false" >
    <xsd:attribute name="id1" >
      <xsd:simpleType>
        <xsd:restriction base="xsd:int" />
      </xsd:simpleType>
    </xsd:attribute>
  </xsd:complexType>

</xsd:schema>

From the Xerces-J 1.4.0 parser I get a cos-nonambig error (IBM's Schema
Quality Checker gives a similar error).

Any suggestions on how to describe this in XML Schema ?

Thank you,

Wouter Cordewiner
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.