Link between bd12 and custom program.

Dear Techies .

Hello !

I am new to ALE IDOC , and was searching a thread where i can get answer related link between bd12 and custom program.

i am trying to send data through BD12, BD14 transaction . but once i execute one of this transaction it should go to my custom program where i mask the data and send it. also i have to extend the idoc CREMAS and DEBMAS.

searching for a correct sequence of linking this all . most important is how can i link my custom program to BD 12 .

Regards