<xs:schema xmlns:xs=“www.w3.org/2001/XMLSchema

         targetNamespace="http://www.tempuri.org/MainSchema"
         xmlns:tns="http://www.tempuri.org/MainSchema"
         xmlns:ns="http://www.tempuri.org/ImportedSchema"
         elementFormDefault="qualified" >
<xs:import namespace="http://www.tempuri.org/ImportedSchema" schemaLocation="./import-455953.xsd" />
<xs:complexType name="MyMainType">
  <xs:sequence>
    <xs:element name="MainA">
      <xs:complexType>
        <xs:attribute name="MainID" type="xs:int"/>
      </xs:complexType>
    </xs:element>
    <xs:element ref="ns:AnotherElement" />
  </xs:sequence>
</xs:complexType>
<xs:element name="MainElement" type="tns:MyMainType">
  <xs:key name="MainKey" >
    <xs:selector xpath="tns:MainA" />
    <xs:field xpath="@MainID" />
  </xs:key>
</xs:element>

</xs:schema>