On criteria for module interfaces

While the benefits of modular software development are widely acknowledged, there is little agreement as to what constitutes a good module interface. Computational complexity techniques allow evaluation of algorithm time and space costs but offer no guidance in the design of the interface to an implementation. Yet, interface design decisions often have a critical effect on the development and maintenance costs of large software systems. Criteria that have led to simple, elegant interfaces are presented in detail. These criteria have been developed and refined through repeated practical application. The use of the criteria is illustrated with concrete examples