<xs:attribute name="TargetSource" use="optional">
    <xs:annotation>
        <xs:documentation xml:lang="en">Specifies to whom the request should be targeted for the information that is to be returned.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="Core">
                <xs:annotation>
                    <xs:documentation xml:lang="en">Requested information should be based on travel data (availabiltiy, rates) stored inhouse.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Vendor">
                <xs:annotation>
                    <xs:documentation xml:lang="en">Requested information should taken from the vendor's system.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>