BAPI and BDC both are used to update data in SAP system.
In BDC we update the data in SAP through transaction.
Using BAPI we can update the data in SAP through transaction and also through database table level updates(i.e. using UPDATE,INSERT,MODIFY,DELETE statements).
In BDC we update the data in SAP through transaction.
Using BAPI we can update the data in SAP through transaction and also through database table level updates(i.e. using UPDATE,INSERT,MODIFY,DELETE statements).