<xs:complexType name="shape">
      <xs:all>
        <xs:element name="id" type="xs:string" />
        <xs:element name="attr2" type="xs:string" />
      </xs:all>
    </xs:complexType>

    <xs:complexType name="circle">
      <xs:complexContent>
         <xs:extension base="shape">
            <xs:all>
               <xs:element name="radius" type="xs:float" />
            </xs:all>
         </xs:extension>
      </xs:complexContent>
    </xs:complexType>