1 STEP)Define an ITAB based on Flat File.
2 STEP)Define an ITAB with ref of BDCDATA Str
3 STEP)Uplaod the data to ITAB Using pd Global class
        CL_GUI_FRONTEND_SERVICES method GUI_UPLOAD.
4 STEP)Call pd Function module BDC_OPEN_GROUP
Provide LOOP to move record from ITAB[] into ITAB.
5 STEP)Refresh ITAB(BDCDATA)
6 STEP)CALL subroutine to place the module POOL program name 
       and screen no in ITAB(BDCDATA).
7 STEP)Call subroutine to place the field name and field value 
       in ITAB(BDCDATA)
8 STEP)CALL pd Function module BDC_INSERT.(provide Mapping)
9 STEP)CALL BDC_CLOSE_GROUP.
Endloop.

call transation                     session
----------------                  -------------------------
1.synchronization is optional    1.only synchronizations
2.error handle explicitly        2.error log     created
3.faster and less amount of      3.slow and we can
transfered     
data can be transfered             large data.
4.it can process single transa   4.we can process multiple 
  cations                          transactions
5.sy-subrc is returns            5. no sy-subrc

coding of call transations
-------------------------
1.we have a flat file with specifed locations
2.we have to declare internal tables like.
   frist one is flat file length.
   second is to define structures of itab2.
   third is define bdcdata
   fourth is bdcmsgcall.
3.we can use call functions like upload,ws_upload,gui_upload
4.we can spilt the flat file data to itab2 structure.
5.we can give the pool file name and screen fields with
subroutines.
6.we can call the screen like that.....
 call transations <tcode> using bdcdata
                  mode < A/E/N>
                  update <A/S>
                  message into internal tables.
7.we can define code inbetween form ..... endform.

session method 
-------------  
1 to 4 steps is same.
5. call the functions module bdc_open_session
6. call the functions module bdc_insert
7. call the functions moudle bdc_close_session