Maintenance

All development processes and costs after delivery of a software product belong to the maintenance phase. Often neglected, this phase is in many cases more costly and more lengthy than the development process before:

New or changed requirements of the customer (41.8%).

Changes in data formats (17.6%).

Emergency fixes (12.4%).

Routine fixes (9%).

Hardware changes (6.2%).

Documentation (5.5%).

Efficiency improvements (4%).

Other (3.4%).

The percentages give the relative maintenance costs that were drawn from a study by Lientz and Swanson in 1980 out of 487 software projects. Despite the age of this study there are no significant differences to newer projects.

Source: Bertrand Meyer, ``Object-Oriented Software Construction'', ``About Software Maintenance''.

	New or changed requirements of the customer (41.8%).
	Changes in data formats (17.6%).
	Emergency fixes (12.4%).
	Routine fixes (9%).
	Hardware changes (6.2%).
	Documentation (5.5%).
	Efficiency improvements (4%).
	Other (3.4%).