The SAP System offers two primary methods for transferring data into the System from other SAP Systems and non-SAP Systems. These two methods are collectively called “batch input” or “batch data communication” ( BDC).Both BDC methods work by carrying out normal SAP transactions, just as a user would. However, BDC can execute the transactions automatically and is therefore suitable for entering large amounts of data that are already available in electronic form. The first processing method could be called “classical batch input” or ” Classical BDC”. In it, an ABAP program reads the external data that is to be entered in the SAP System and stores the data in a “BDC session.” A session stores the actions that are required to enter your data using normal SAP transactions.This method uses the function modules BDC_OPEN, BDC_INSERT, and BDC_CLOSE to generate sessions. In the second method, your program uses the ABAP CALL TRANSACTION USING statement to run an SAP transaction.BDC data does not have to be deposited in a session for later processing. Instead, the entire BDC process takes place inline in your program. There is a third BDC method using the ABAP CALL DIALOG statement. However, SAP recommends against using this method unless necessary. The CALL DIALOG method is now outdated and is more complex and less comfortable to use than the other techniques. All these three BDC methods use a common data structure for holding the instructions and data for SAP transactions. This structure is defined as structure BDCDATA in the ABAP Dictionary.