XML Upload- download

Hi

I want to upload an XML file from the presentaion server and then my class method will process it and convert into another xml structure, that file needs to be downloaded to presentaion server back

My method import/export parameters are

SOURCE Importing Type XSTRING

PARAM Importing Type Ref To IF_MAPPING_PARAM

TRACE Importing Type Ref To IF_MAPPING_TRACE

DYNAMIC_CONFIGURATION Importing Type Ref To IF_MAPPING_DYNAMIC_CONF

RESULT Exporting Type XSTRING

source is source xml file and result is the targrt xml file .......

Any ideas ?????

Regards

Swatantra