<schema xmlns="http://www.ascc.net/xml/schematron" >
     <pattern name="Open model">
          <rule context="AAA">
               <assert test="BBB"> BBB element is not present</assert>
               <assert test="CCC"> CCC element is not present</assert>
          </rule>
     </pattern>
     <pattern name="Closed model">
          <rule context="AAA">
               <assert test="BBB"> BBB element is not present</assert>
               <assert test="CCC"> CCC element is not present</assert>
               <assert test="count(BBB|CCC) = count (*)">There is an extra element</assert>
          </rule>
     </pattern>
</schema>
