<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns="http://FOO" targetNamespace="http://FOO">

        <xs:element name="foo">
                <xs:complexType>
                        <xs:complexContent>
                                <xs:restriction base="typeA">
                                        <xs:attribute name="barA" type="xs:string" use="optional"/>
                                </xs:restriction>
                        </xs:complexContent>
                </xs:complexType>
        </xs:element>

        <xs:complexType name="typeA">
                <xs:attribute name="barA" type="xs:string" use="required"/>
        </xs:complexType>

</xs:schema>