What is bdc

Question

can anyone tell me what is bdc

Answer 1

Data Transfer 
BDC
Batch Data Communication
It is used to transfer data from Sap to Sap or from Non Sap to sap system. It uses the normal transaction codes to transfer the data.
Data Transfer Methods 
You can use the following methods to transfer data:
•        CALL TRANSACTION: Data consistency check with the help of screen logic.
•        Batch input with batch input sessions: Data consistency check with the help of screen logic
Difference between Batch Input and CALL TRANSACTION
If the direct input cannot be used for your task, this makes creating a data transfer program easier since the underlying transactions ensure that the data consistency checks are executed.
In the case of an error during the data transfer (if data records are inconsistent, for example), you can restart the transfer at the point in the program where the error occurred.
Data Transfer Overview
Batch input methods
With the batch input method, an ABAP program reads the external data that is to be entered in the SAP 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.
CALL TRANSACTION methods
In the second method, your program uses the ABAP statement CALL TRANSACTION USING to run an SAP transaction. External data does not have to be deposited in a session for later processing. Instead, the entire batch input process takes place inline in your program.
Choosing Data Transfer Methods
Selecting a Data Transfer Method  
When you transfer data in ABAP, you have three options to submit the data for the data transfer. Only the first two methods can be recommended without reservation. The third method, by way of CALL DIALOG, is outmoded. CALL DIALOG is less comfortable than the other methods. You should use it only if you must.
•     Use the CALL TRANSACTION USING statement
Summary: With CALL TRANSACTION USING, the system processes the data more quickly than with batch input sessions. Unlike batch input sessions, CALL TRANSACTION USING does not automatically support interactive correction or logging functions.
Your program prepares the data and then calls the corresponding transaction that is then processed immediately.
The most important features of CALL TRANSACTION USING are:
o     Synchronous processing
o     Transfer of data from an individual transaction each time the statement CALL TRANSACTION USING is called
o     You can update the database both synchronously and asynchronously
The program specifies the update type
o     Separate LUW (logical units of work) for the transaction
The system executes a database commit immediately before and after the CALL TRANSACTION USING statement
o     No batch input processing log
•     Create a session on the batch input queue.
Summary: Offers management of sessions, support for playing back and correcting sessions that contain errors, and detailed logging.
Your program prepares the data and stores it in a batch input session. A session is a collection of transaction data for one or more transactions. Batch input sessions are maintained by the system in the batch input queue. You can process batch input sessions in the background processing system.
Your program must open a session in the queue before transferring data to it, and must close it again afterwards. All of these operations are performed by making function module calls from the ABAP program.
The most important aspects of the session interface are:
o     Asynchronous processing
o     Transfers data for multiple transactions
o     Synchronous database update
During processing, no transaction is started until the previous transaction has been written to the database.
o     A batch input processing log is generated for each session
o     Sessions cannot be generated in parallel
The batch input program must not open a session until it has closed the preceding session.
Executing Data Transfer Programs 
Procedure
If you are using an SAP data transfer program, follow the procedure specified in the program documentation.
If you are using a generated data transfer program, proceed as follows:
1.     Start the data transfer program.
2.     Decide which batch input method you want to use for the data transfer.
a) CALL TRANSACTION USING:
You must specify the:
– Processing mode: You use this parameter to specify whether processing should take place in the background or in dialog mode.
Possible values are:
A     Display all
E     Display only errors
N     No display
– Update mode: This parameter determines how the data is to be updated:
Possible values are:
S     Synchronous
A     Asynchronous
L     Local update
– Error session: Here you have the option to specify a session name for a batch input session in which data is to be written in the case of an error. You can use this to identify incorrect data records after the batch input program has run and to import the records into the R/3 System once you have corrected them.
If you are creating an error session, you must also specify:
– User: Specify the user with whose authorizations the sessions are processed.
– Keep session: This specifies whether or not the session should be deleted once it has been processed.
– Lock date: Specify the processing date for the error session.
b) Generate session:
– Session name: Specify a name for the batch input session to be generated.
– User: Specify the user with whose authorizations the sessions are processed.
– Keep session: This specifies whether or not the session should be deleted once it has been processed.
– Lock date: Specify the processing date for the error session.
3.     Specify a character that is to be used as the NODATA character.
4.     Specify the path of the data file from which the data is to be imported into the R/3 System.
5.     Execute the program.
6.     If you have generated a session, or if errors occurred in CALL TRANSACTION USING mode, you must now edit the generated sessions. You can find information on this in BC - System services in  batch input sessions.
Creating a Session with BDC_OPEN_GROUP  
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.
You cannot re-open a session that already exists and has been closed. If you call BDC_OPEN_GROUP with the name of an existing session, then an additional session with the same name is created.
A batch input program may have only one session open at a time. Before opening a session, make sure that any sessions that the program closes any sessions that it previously had opened.
BDC_OPEN_GROUP takes the following EXPORTING parameters:
•        CLIENT
Client in which the session is to be processed.
Default: If you don't provide a value for this parameter, the default is the client under which the batch input program runs when the session is created.
•        GROUP
Name of the session that is to be created. May be up to 12 characters long.
Default: None. You must specify a session name.
•        HOLDDATE
Lock date. The session is locked and may not be processed until after the date that you specify.  Only a system administrator with the LOCK authorization for the authorization object Batch Input Authorizations can unlock and run a session before this date.
Format: YYYYMMDD (8 digits).
Default: No lock date, session can be processed immediately. A lock date is optional.
•        KEEP
Retain session after successful processing. Set this option to the value X to have a session kept after it has been successfully processed. A session that is kept remains in the input/output queue until an administrator deletes it.
Sessions that contain errors in transactions are kept even if KEEP is not set.
Default: If not set, then sessions that are successfully processed are deleted. Only the batch input log is kept.
•        USER
Authorizations user for background processing. This is the user name that is used for checking authorizations if a session is started in background processing. The user must be authorized for all of the transactions and functions that are to be executed in a session. Otherwise, transactions will be terminated with “no authorization” errors.
The user can be of type dialog or background. Dialog users are normal interactive users in the SAP system. Background users are user master records that are specially defined for providing authorizations for background processing jobs.
Advantages:
Types of BDC :
CLASSICAL BATCH INPUT (Session Method)
CALL TRANSACTION
Session method.
1) synchronous processing.
2) can tranfer large amount of data.
3) processing is slower.
4) error log is created
5) data is not updated until session is processed.
Call transaction.
1) asynchronous processing
2) can transfer small amount of data
3) processing is faster.
4) errors need to be handled explicitly
5) data is updated automatically