1  <schema xmlns="http://www.ascc.net/xml/schematron" >
2       <pattern name="Attributes present">
3            <rule context="BBB">
4                 <assert test="not(@aaa) or (@aaa and @bbb)">The element must not have an isolated aaa attribute</assert>
5                 <assert test="not(@bbb) or (@aaa and @bbb)">The element must not have an isolated bbb attribute</assert>
6            </rule>
7       </pattern>
8  </schema>