What is SAP ABAP BDC and How you use it?

BC Basis Components-

-ABAP workbench-
-BC Basis Programming interfaces
--Data transfer

During data transfer, data is transferred from an external system into the SAP
R/3 System. •Transfer data from an external system into an R/3 System as it is
installed. •Transfer data regularly from an external system into an R/3 System.

Example: If data for some departments in your company is input using a system
other than the R/3 System, you can still integrate this data in the R/3 System. To do
this, you export the data from the external system and use a data transfer method to
import it into the R/3 System.
Batch input with batch input sessions : Data consistency check with the help of
screen logic.

With the batch input method, an ABAP program reads the external data that is to be
entered in the R/3 System and stores the data in a "batch input session". The
session records the actions that are required to transfer data into the system using
normal SAP transactions.

When the program has generated the session, you can run the session to execute
the SAP transactions in it. You can explicitly start and monitor a session with the
batch input management function (by choosing System ® Services ® Batch input), or
have the session run in the background processing system.

Use the BDC_OPEN_GROUP function module to create a new session. Once you
have created a session, then you can insert batch input data into it with
BDC_INSERT. Use the BDC_INSERT function module to add a transaction to a
batch input session. Use the BDC_CLOSE_GROUP function module to close a
session after you have inserted all of your batch input data into it.