Components

A component, at least for sake of this discussion, is a routine or module. In C++ a component might be an object / class.

Routines and Modules

routine

The quality of routines in a program have a tremendous impact on the reliability of that program.

A module is a collection of objects that are logically related. These may include constants, data types, variables, and program units. (routines)

Characteristic of all design methods.
Components have clearly defined inputs and outputs, and clearly stated purpose.
Easy to examine each component separately.
Organized in a hierarchy so the system can be investigated one level at a time.
Components at one level refine those in the level above.
The more abstract top levels hide the details of lower level functional or data components