One of the key concepts for an ABAP programmer to understand is that of function modules. Recently, I discussed the concept of function groups within ABAP. Today, lets us focus on function modules. From a definition viewpoint, function modules can be defined a modular units with interfaces that can be called from any ABAP programs. And since function modules operate on sAP objects, function modules which operate on the same object can be combined to form a function group.

SAP has integrated function modules within the ABAP workbench. Since the function module contains interfaces, the interface can contain import export parameters, changing parameters and even exceptions. To explain in a bit more detail:

Import Parameters are sent to the function modules from other programs and are assigned to standard ABAP dictionary types. Export parameters on the other hand are passed from the function module to the calling program. Since the export parameters are optional, they may or may not be accepted by the calling program. Parameters known as changing parameters can be sent to the function module, however the function module can change such parameters. Lastly, exceptions are used to note errors. An error may cause the function module to stop since it may trigger an exception. Exceptions can be assigned to numbers in the calling program, and SAP will use the field SY-SUBRC to generate values.

Another important point to consider is processing type of a function module. For example, remote enabled function modules can be called asynchronously in the same system and can also be called from other Non SAP systems. However, a valid system connection must exist before the function module can be called. Update function modules on the other hand, contain additional functions for enabling database changes. Function modules thus are easier to use than ABAP Sub Routines and are an core part of a function group.

You may also like the below

Transport Request in SAP
SAP R3 Performance Tuning Basics
SAP SOLMAN Solution Manager Toolset
SAP Role Maintenance Adminstration Tool