Modularity with clean interfaces

The user's program views an abstract object through a small number of functions which modify the state of the object. Any changes in the algorithms used for these functions, or the internal state representation, are not directly visible to the using program. Thus only a small number of programs depend on the internal state representation, and they can be collected together in a single module. This is very similar to the form of modularization proposed by D. L. Parnas [P1].