Maintainability
Software is maintainable if it can be modified easily after a version release (internal or external)
- improvements rather than upkeep as in other engineered products
- evidence shows that maintenance costs exceed 60% of total software costs
Corrective maintenance: removal of residual faults, or “bugs”, in software after delivery (~20%)
Adaptive maintenance: adjusting software to changes in application environment (~30%)
Perfective maintenance: changing software to improve qualities (~50%)