<xs:simpleType name="DateValueExtensionType">
  <xs:annotation>
    <xs:appinfo>
      <mdr:definition>Type used to modify the type modeling date to allow "Not Applicable" and "Unknown".</mdr:definition>
    </xs:appinfo>
  </xs:annotation>
  <xs:restriction base="xs:string">
    <xs:enumeration value="Not Applicable"/>
    <xs:enumeration value="Unknown"/>
  </xs:restriction>
</xs:simpleType>