<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" 
        targetNamespace="http://www.example.org" 
        xmlns:ex="http://www.example.org"
        elementFormDefault="qualified">

     <element name="Document">
         <complexType>
             <sequence>
                 <element ref="ex:What"/>
                 <element ref="ex:Payload"/>
             </sequence>
         </complexType>
     </element>

     <element name="What">
         <complexType>
             <attribute name="taxonomy" use="required" type="anyURI"/>
         </complexType>
     </element>

     <element name="Payload">
         <complexType mixed="true"/>
     </element>
</schema>