the top-down approach to solution development

Following is an example of how Top Down programming works. It starts with a system, them breaks down to programs, modules, routines and subroutines that are themselves a set of statements.

a system comprises all the programs in the suite (and gets described by a System Flowchart. At this level, data movement is defined by Context diagrams)

a program comprises all of the modules required to perform the required task (the data between modules can be described in structure charts)

a module is a group of subroutines that together achieve a subtask (dataflow between modules can be defined by dataflow diagrams)

a subroutine is a set of statements that performs a single logical task (the modules are defined by algorithms or pseudocode)