test/schemas/import-455953.xsd

<?xml version='1.0' encoding='UTF-8'?>
<xs:schema targetNamespace="http://www.tempuri.org/ImportedSchema" elementFormDefault="qualified" xmlns:tns="http://www.tempuri.org/ImportedSchema" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  
  <xs:complexType name="AnotherType">
    <xs:sequence>
      <xs:element name="B">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="MyB" type="xs:string" />
          </xs:sequence>
          <xs:attribute name="BID" type="xs:int"/>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>

  <xs:element name="AnotherElement" type="tns:AnotherType">
    <xs:key name="AnotherKey">
     <xs:selector xpath="tns:B"/>
     <xs:field xpath="@BID"/>
    </xs:key>
  </xs:element>

</xs:schema>