<xs:complexType name="IfcOpeningElementType">
    <xs:complexContent>
      <xs:extension base="uro:IfcElementType">
        <xs:sequence>
          <xs:element name="nominalArea" minOccurs="0" type="gml:MeasureType"/>
          <xs:element name="nominalVolume" minOccurs="0" type="gml:MeasureType"/>
        </xs:sequence>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>