26 Function Modules in SAP ABAP
Function Modules in SAP ABAP are independent, reusable cross-program procedures encapsulated inside a centralized system library. They are managed using the Function Builder via transaction code SE37. Unlike internal subroutines, they have a strictly defined data exchange interface and can be called from any global ABAP program.
Function Groups: The Containers
Every function module must reside inside a Function Group, which serves as a logical container for related modules.A function module cannot exist on its own; it must belong to a Function Group.
A function group acts as a logical bucket or container for FMs that share common business purposes (e.g., HR payroll logic).
When you activate a function group, the system automatically creates a main program comprising two underlying files:
Top Include: A global area where variables and data structures are defined, making them shared and accessible across every FM within that group.
UXX Include: A framework file containing structural links to the individual source code blocks of your FMs.