XML schema and OO Overriding

[courtis]

How do I override an element with out losing my inheritance? Using the following:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="[URL unfurl="true"]http://www.w3.org/2001/XMLSchema"[/URL] elementFormDefault="qualified" attributeFormDefault="unqualified">
	<xs:element name="vehicles">
		<xs:annotation>
			<xs:documentation>Comment describing your root element</xs:documentation>
		</xs:annotation>
		<xs:complexType>
			<xs:sequence>
				<xs:element ref="car"/>
			</xs:sequence>
		</xs:complexType>
	</xs:element>
	<xs:element name="car" type="carType"/>
	<xs:complexType name="vehicleType">
		<xs:all>
			<xs:element name="type">
				<xs:simpleType>
					<xs:restriction base="xs:string">
						<xs:enumeration value="car"/>
						<xs:enumeration value="motorcycle"/>
						<xs:enumeration value="truck"/>
						<xs:enumeration value="boat"/>
					</xs:restriction>
				</xs:simpleType>
			</xs:element>
			<xs:element name="transmissiontype">
				<xs:simpleType>
					<xs:restriction base="xs:string">
						<xs:enumeration value="manual"/>
						<xs:enumeration value="automatic"/>
					</xs:restriction>
				</xs:simpleType>
			</xs:element>
			<xs:element name="numberofwheels">
				<xs:simpleType>
					<xs:restriction base="xs:decimal">
						<xs:minInclusive value="2"/>
						<xs:maxInclusive value="18"/>
					</xs:restriction>
				</xs:simpleType>
			</xs:element>
		</xs:all>
	</xs:complexType>
	<xs:complexType name="carType">
		<xs:complexContent>
			<xs:extension base="vehicleType"/>
		</xs:complexContent>
	</xs:complexType>
</xs:schema>

If I wanted to override type so that it had a fixed value of car and the maxInclusive on numberofwheels to be 4, I could make the element car a restriction of carType like so:

	<xs:element name="car">
		<xs:complexType>
			<xs:complexContent>
				<xs:restriction base="carType">
					<xs:all>
						<xs:element name="type" fixed="car">
							<xs:simpleType>
								<xs:restriction base="xs:string"/>
							</xs:simpleType>
						</xs:element>
						<xs:element name="transmissiontype">
							<xs:simpleType>
								<xs:restriction base="xs:string">
									<xs:enumeration value="manual"/>
									<xs:enumeration value="automatic"/>
								</xs:restriction>
							</xs:simpleType>
						</xs:element>
						<xs:element name="numberofwheels">
							<xs:simpleType>
								<xs:restriction base="xs:decimal">
									<xs:minInclusive value="2"/>
									<xs:maxInclusive value="4"/>
								</xs:restriction>
							</xs:simpleType>
						</xs:element>
					</xs:all>
				</xs:restriction>
			</xs:complexContent>
		</xs:complexType>
	</xs:element>

However if I go back to vehicleType and add another element like lights I have to also go back and add it to the restriction elements too, car in this case.