Conversion from ABAP into XML

Hi,

I am trying to convert data of internal table into XML, using below code

TYPES : BEGIN OF tp_vbap,

           vbeln TYPE vbap-vbeln,

           posnr TYPE vbap-posnr,

           matnt TYPE vbap-matnr,

         END OF tp_vbap.

DATA : tl_vbap TYPE STANDARD TABLE OF tp_vbap.

DATA : l_object TYPE REF TO cl_xml_document.

SELECT vbeln posnr matnr FROM vbap INTO TABLE tl_vbap  UP TO 100 ROWS.

CREATE OBJECT l_object.

l_object->create_with_data( dataobject =  tl_vbap ).

l_object->export_to_file( filename = l_pathtext ).

But in XML file all fields i get are in CAPITAL, like VBELN andd POSNR.I want it to be case sensitive.

How to do that?

Thanks.