<?xml version=“1.0”?> <xs:schema xmlns:xs=“www.w3.org/2001/XMLSchema”>

<xs:complexType name="Item" abstract="true">
 <xs:sequence minOccurs="1" maxOccurs="unbounded">
   <xs:element name="Name" type="xs:string"/>
 </xs:sequence>
</xs:complexType>

<xs:complexType name="ItemWithNumber">
 <xs:complexContent>
  <xs:extension base="Item">
   <xs:sequence>
    <xs:element name="Number" type="xs:nonNegativeInteger"/>
   </xs:sequence>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

<xs:element name="ItemsList">
 <xs:complexType>
  <xs:sequence>
   <xs:element name="Item" type="Item" maxOccurs="unbounded"/>
  </xs:sequence>
 </xs:complexType>
</xs:element>

</xs:schema>