Problem with Sum function

Hi:

My xml file looks like this:

<node1>
      <childnode1a>
             <childnode11a>
                     <value></value>
               </childnode11a>
       </childnode1a>
</node1>

There can be any number of <childnode11a> elements containing <value>.
Now, I am trying to compute the sum(value). Instead of giving me a
total sum of all the rows, it display the values individually. I
believe we have to use recursion. Can anyone please help me with this
problem?

Thanks