This discusses how modularity helps to make complexity in software system manageable. The most import measure of Complexity is the financial cost associated with software maintenance: i.e., the cost required to change a System. A number of independent studies concur that software maintenance accounts for ~80% of the total lifetime cost of a software system: e.g., Erlikh, L. (2000) determined that 80% of software costs are concerned with evolution of the software.
