<xs:element name="ContractIdentifier" >
  <xs:annotation>
    <xs:documentation>Common Contract Identifier for the Contract.  If the contract is issued by a 3rd party system, such as a B2B  system, the system is identified in the documentCreatorIdentifier child element</xs:documentation>
  </xs:annotation>
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="documentCreatorIdentifier"/>
      <xs:element ref="documentNumber"/>
      <xs:element minOccurs="0" ref="documentVersion"/>
      <xs:element minOccurs="0" name="contractExtension" type="xs:string">
        <xs:annotation>
          <xs:documentation>Identifier or code to identify the sub-contract or contract extension or shipment number to which this document pertains, if the contract is fixed in parts</xs:documentation>
        </xs:annotation>
      </xs:element>
    </xs:sequence>
  </xs:complexType>
</xs:element>