Modularization techniques

The ABAP programs have processing blocks, those which are called by run-time environment i.e Event blocks and Dialog modules, and those which are called by ABAP programs i.e Function modules, Methods and Sub-routines. Refer to the following link from SAP Help to know about the modularization techniques in ABAP:

http://help.sap.com/saphelp_nw04/helpdata/en/9f/db970e35c111d1829f0000e829fbfe/frameset.htm