<xs:element name="UnitCharacteristics"> <xs:complexType> <xs:sequence> <xs:element ref="Height" minOccurs="0" /> <xs:element ref="Thickness" minOccurs="0" /> <xs:element ref="Width" minOccurs="0" /> <xs:element ref="Weight" minOccurs="0" /> </xs:sequence> </xs:complexType> </xs:element>