BDC is a method for transfer data in SAP. Data that you want it to be operated by BCD must have structure as bellows:

BDCDATA Structure

Field Name     Type        Description
PROGRAM        CHAR(40)    Program Name
DYNPRO         NUMC(4)     Screen No.
DYNBEGIN       CHAR(1)     Begin a screen (If yes then equal ’X’)
FNAM           CHAR(132)   Field Name
FVAL           CHAR(132)   Field Value