<?xml version="1.0" encoding="UTF-8"?>
<xs:schema     
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   targetNamespace="http://sample.com/procure"
   xmlns:po="http://sample.com/procure"
   elementFormDefault="qualified">
   <xs:include schemaLocation="included.xsd"/>
   <xs:element name="purchase-order">
       <xs:complexType>
           <xs:sequence>
               <xs:element name="customer" type="po:customer"/>
               <xs:element name="shipper" type="po:shipper" minOccurs="0"/>
           </xs:sequence>
       </xs:complexType>
   </xs:element>
</xs:schema>
