a help for newbie

[lood]

Hello,
I'm looking for a script to search in xml like that

<?xml....>
<global>

   <parent name="A" age="40" add="DDD">
 
 	 <child x="..." y="..." z="..." i="...">
   	 	      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
          </child>

          <child x="..." y="..." z="..." i="...">
   	 	      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
          </child>

.
.
.
   </parent>
.
   <parent name="B" age="50" add="FFF">
 
 	 <child x="..." y="..." z="..." i="...">
   	 	      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
          </child>

          <child x="..." y="..." z="..." i="...">
   	 	      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
   		      <data a="..." b="..."/>
          </child>

.
.
.
   </parent>
.
.
.
</global>

I want to search by "a" in "data" (may occur more than once)
and display everything in "child".

Thanks in advance.