Classic BAdIs 
Business Add-Ins (BAdIs) are enhancements to the standard version. 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.
***************************************************************************************************************************
This
documentation describes the classic BAdIs that have replace function modules
exits since Release 4.6d. As of Release 7.0 of the SAP NetWeaver Application
Server ABAP (SAP NetWeaver 2004s), there is a new type of BAdI. Creation of
these BAdIs is integrated into the 
Enhancement
Framework. Execution of these BAdIs is integrated, for performance
reasons, into the ABAP language. The new BAdIs have
completely replaced the classic BAdIs. A migration tool is
available for converting the classic BAdIs into new BAdIs.
***************************************************************************************************************************
As with customer
exits, two different views are available:
· In the definition view, an application programmer defines exit points in a source that allow specific industry sectors, partners, and customers to attach additional coding 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 solution, 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, country-specific versions, industry solutions, partner, customer, and so on). You can create definitions and implementations of Business Add-Ins at any level of the system landscape.
SAP guarantees the upward compatibility of all Business Add-In interfaces. Release upgrades do not affect enhancement calls from within the standard software nor do they affect the validity of call interfaces. You do not have to register Business Add-Ins in SSCR.
The Business Add-In enhancement technique differentiates between enhancements that can only be implemented once and enhancements that can be used actively by any number of customers at the same time. In addition, Business Add-Ins can be defined according to filter values. This allows you to differentiate between Add-In implementations using the filter Country or other criteria.
The enhancement technique is set up in such a way that it is possible to define interfaces for ABAP source code, screens, GUI interfaces, and tables. These allow customers to include their own enhancements in the standard. A single Business Add-In contains all of the interfaces necessary to implement a specific task.
The actual
program code is enhanced using ABAP Objects. In order to better understand the
enhancement technique behind the Business Add, we recommend reading the
section ABAP
Objects.
For more information, see the following sections:
Architecture of the Enhancement Technique
Comparison With Previous Techniques
Definition of a Business Add-In
Calling a Business Add-In in the Application Program
Implementing a Business Add-In
Filter-Dependent Business Add-Ins
Business Add-Ins: Import Procedure