Fred Brooks, in his key book The Mythical Man-Month,[1] states that over 90% of the costs of a typical system arise in the maintenance phase, and that any successful piece of software will inevitably be maintained.
In fact, Agile methods stem from maintenance-like activities in and around web based technologies, where the bulk of the capability comes from frameworks and standards.[citation needed]
Software maintenance address bug fixes and minor enhancements and software evolution focus on adaptation and migration.