need xpath help please

i'am testing an xml structure:

<Articles>


...


   <Article ID="333">

     <author>Paul</author>

     <title>i hate xpath </title>

        <child1>bla</child1>

       <child2>blabla
          <subchild>
             <subsubchild DEEP = "Attribute"></subsubchild>     //this is my nightmare
          </subchild>
       </child2>

       <child3>testing</child3>

   </Article> 
...

</Articles>

what xpath expression will fetch and update the subsubchild attrib value ? i am mostly concerned with fetching and updating sub values of any node, no matter how deeply or superficially located, if the parent ID (333 in this case). is known ? currently i have used :

$query= "//*[@ID=333]//*node()[@DEEP and @DEEP = "Attribute"]";
$outcome = $xml->xpath($query);
    echo isset($outcome[0][0]) ? "found" : "unavailable";

and several more related xpressions, they're all fraustrating my efforts with Invalid expression report. can anyone be of help please ?