importing elements from multiple namespaces and defining their sc hemaLocations in a corresponding XML data file

Let's say I have a complexType "twoFoosType" made up of two elements named "foo" from different namespaces and a global element "twoFoos" that uses this complexType:
 
    <xsd:element name="twoFoos" type="twoFoosType"/>
    <xsd:complexType name="twoFoosType">
        <xsd:element ref="ns1:foo"/>
        <xsd:element ref="ns2:foo"/>
    </xsd:complexType>
 
How do I use "twoFoos" in an XML data file and give the schemaLocation of "twoFoos" and the two "foo" elements?  I assume that this structure is partially correct...
 
    <twoFoos xmlns="http://www.foo.com" xmlns:ns1="http://www.foo.com/ns1" xmlns:ns2="http://www.foo.com/ns2">
        <ns1:foo/>
        <ns2:foo/>
    </twoFoos>
 
...but I am not clear how to define the schemaLocation for all three namespaces.
 
thanks in advance, Chuck
 
Chuck Han, Data Architect
Autodesk, Inc.
+1.415.507.8742