Websphere Message Broker: Accessing XML elements in ESQL

Websphere Message Broker: File in File out example. I have an XML file with repeating element structure. How can I access and modify value of a particular element in ESQL. I worte following code..

CREATE PROCEDURE CopyEntireMessage() BEGIN
     --SET OutputRoot = InputRoot;
      DECLARE I INTEGER 1;
      DECLARE J INTEGER;
      SET J = CARDINALITY(OutputRoot.*[]);
      WHILE I < J DO
         SET OutputRoot = InputRoot;
         SET OutputRoot.XMLNS.student[I].name = 'XYZ';
         SET I = I + 1;
      END WHILE;
 END;

But its not working. Picking up the file from input folder but i cannot see anything in Output folder. But if I comment

SET OutputRoot.XMLNS.student[I].name = 'XYZ';

then file is available in output folder as it is without any change.

My XML file is as below

<person>
 <student>
   <name>ABC</name>
   <age>20</age>
   <address>city1</address>
 </student>
 <student>
   <name>PQR</name>
   <age>20</age>
   <address>city2</address>
 </student>
</person>

can anybody help me on this?