How bapi different from session and call transaction?

Question

how bapi different from session and call transaction?
thanks in advance.

Answer 1

For one, Batch Data Communication (BDC) is older. Business Application Programming Interface (BAPI) came later, about 10 years ago (you can see this already from the name, which contains marketese like "business" ).
More important though, they are different technologies. With BDC you build the "batch input transaction" yourself, with an ABAP program which creates the "batch input session" ("Batch-Input-Mappe" in german). You then take that session, like an object, and "run" it on a system (most of the time, this is done on a local system by the administrators, after it has been tested for correctness).
With BAPI, a system (local or remote) exposes its interface to you through some kind of Remote Function Call (RFC). Practically, it tells you: "What do you want to do? Insert that data into Materials Management? Here is the function and the the parameters you have to use for each record". You only work with the Interface - the exposed function. How this function works does not have to interest you. You don't have sessions to "run", you fire your function calls filled with data, one after another and you're done.
BAPI can be run remotely. With BDC, you probably have to call the administrators of the remote system and send them the session you created for them to run. With BDC you go through the whole transaction in one BDC session, with BAPI you may need more than one "BAPI calls" to do this.
With BAPI you don't fill obcure field names with values, you just fill the parameters. You can use a BAPI from inside your ABAP program to let a "business object" do some clearly defined work for you, then you can continue with your code doing other things. You don't do this with BDC. With BDC you write a dedicated program that creates the "session", which is then executed separately.
Batch Data Communication (BDC) is the oldest batch interfacing technique that SAP provided since the early versions of R/3. BDC is not a
typical integration tool, in the sense that, it can be only be used for uploading data into R/3 and so it is not bi-directional.
BDC works on the principle of simulating user input for transactional screen, via an ABAP program. Typically the input comes in the form of a flat file. The ABAP program reads this file and formats the input data screen by screen into an internal table (BDCDATA). The transaction is then started using this internal table as the input and executed in the background.
In Call Transaction, the transactions are triggered at the time of processing itself and so the ABAP program must do the error handling.
It can also be used for real-time interfaces and custom error handling & logging features. Whereas in Batch Input Sessions, the ABAP
program creates a session with all the transactional data, and this session can be viewed, scheduled and processed (using Transaction SM35) at a later time. The latter technique has a built-in error processing mechanism too.
Batch Input (BI) programs still use the classical BDC approach but doesnt require an ABAP program to be written to format the
BDCDATA. The user has to format the data using predefined structures and store it in a flat file. The BI program then reads this and
invokes the transaction mentioned in the header record of the file.
Direct Input (DI) programs work exactly similar to BI programs. But the only difference is, instead of processing screens they validate
fields and directly load the data into tables using standard function modules. For this reason, DI programs are much faster (RMDATIND - Material Master DI program works at least 5 times faster) than the BDC counterpart and so ideally suited for loading large volume data. DI programs are
not available for all application areas.
Business Add-In (BADI) are a new SAP enhancement technique based on ABAP Objects.
They can be inserted into the SAP System to accommodate user requirements too specific to be included in the standard delivery. Since specific industries often require special functions, SAP allows you to predefine these points in your software.
As with customer exits two different views are available:
In the definition view, an application programmer predefines exit points in a source that allow specific industry sectors, partners, and customers to attach additional software to standard SAP source code without having to modify the original object.
In the implementation view, the users of Business Add-Ins can customize the logic they need or use a standard logic if one is available.
In contrast to customer exits, Business Add-Ins no longer assume a two-level infrastructure (SAP and customer solutions), but instead allow for a multi-level system landscape (SAP, partner, and customer solutions, as well as country versions, industry solutions, and the like). Definitions and implementations of Business Add-Ins can be created at each level within such a system infrastructure.