<mapping>
      <class name="Root">
          <field name="children" collection="map">
             <bind-xml>
                <class name="org.exolab.castor.mapping.MapItem">
                   <field name="key" type="string">
                      <bind-xml name="id"/>
                   </field>
                   <field name="value" type="string"/>
                </class>
             </bind-xml>
          </field>
      </class>
</mapping>
