All ABAP programs are modular in structure and made up of processing blocks (see Structure of Processing Logic). There are two kinds of processing blocks, those that are called from outside a program by the ABAP runtime system, and those that can be called by ABAP statements in ABAP programs.
Processing blocks that are called using the ABAP runtime system:
· Event Blocks
· Dialog Modules
Processing blocks that are called from ABAP programs:
· Function modules
· Methods (see ABAP Objects)
The processing blocks that you call from ABAP programs are called procedures.
As well as modularization in processing blocks, ABAP allows you to modularize source code by placing ABAP statements either in local macros or global include programs.
The modularization of ABAP programs in event blocks and dialog modules serves for general execution of ABAP programs while modularization in procedures and source code modules serves for improving the readability and maintainability of ABAP programs, prevention of redundancies, reusability of functions, and the encapsulation of data.