BDC Recording

I want to call a transaction with BDC recording,

like

CALL TRANSACTION 'VL74' USING T_bdcdata

MODE 'N'

UPDATE c_syn

MESSAGES INTO T_messtab.

After processing from the first screen of VL74,

it goes to the next screen which is a ALV display.

In this ALV display a record is to be selected, by the checkbox which is displayed

in front of it.

While doing the recording in SHDB for the same process as described above,

I am not getting the name of the checkbox which is to be marked as 'X',

to fill my T_bdcdata.

Can anyone help me in getting the name of the checkbox which I can use in filling the

bdc data??