SAP created the Business Framework to allow the technical integration and exchange of business data among SAP components and between SAP and non-SAP components. Important components of the Business Framework are the Business Application Programming Interfaces (BAPIs), which represent visible interfaces at the component boundaries and whose properties serve to integrate these components. 

The integration can include both components within a local network and components that are connected with one another through the Internet.

BAPIs allow integration at the business level, not the technical level. This provides for greater stability in the link, and independence from the underlying communication technology.

You can get all the standard SAP BAPI functions with the transactions code 'BAPI'.

BAPI Programming Reference Books
SAP R/3 Interfacing Using BAPIs; A Practical Guide to Working within the SAP Business Framework with CDROM

ABAP Certification Books
ABAP Programming: A Guide to the Certification Course

BAPI - Business Application Programming Interface
BAPI Conventions
What is the different between ALE, IDOC and BAPI?
BAPI Licensing
BAPI and ABAP objects
Difference and/or similarities between BAPI and IDOC's
BAPI vs Call transaction
COMMIT WORK and BAPI_TRANSACTION_COMMIT
Exponential form to general
persistent key
read function module definition
Difference Between BAPI and RFC
BAPI ActiveX Control
ODBC and MsAccess
BAPI C++ Library
Bapi's Customizing
Questions on BAPI and RFC Programming
How to Find Bapi for Particular Transaction in SAP
BAPI Step by step Guidance

HR BAPI
BAPI_EMPLOYEE_CHECKPASSWORD
HR-TM Object

Logistics BAPI
BAPI_GOODSMVT_CREATE to post Goods Movement
BAPI to Copy Materials from one Plant to Another
BAPI_MATERIAL_MAINTAINDATA_RT
Material Master creation/change
Material Master
Sample Abap code on BAPI_PO_CHANGE
BAPI_ALM_NOTIF_CREATE - Maintenance Notification
BAPI to create Sales Order with reference
BAPI_SALESORDER_CREATEFROMDAT2 - Sales Order Create
BAPI and JAVA Program to Interface Two System

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