What are the three different types of software maintenance and how is effort distributed across these maintenance types?

What are the three different types of software maintenance and how is effort distributed across these maintenance types?
Answer: There are three different types of software maintenance:

1. Fault repairs: Coding errors are usually relatively cheap to correct; design errors are more expensive as they may involve rewriting several program components. Requirements errors are the most expensive to repair because of the extensive system redesign which may be necessary.

2. Environmental adaptation: This type of maintenance is required when some aspect of the system’s environment such as the hardware, the platform operating system, or other support software changes. The application system must be modified to adapt it to cope with these environmental changes.

3. Functionality addition: This type of maintenance is necessary when the system requirements change in response to organizational or business change. The scale of the changes required to the software is often much greater than for the other types of maintenance.

Effort distribution:

Fault Repair (17%), Environmental Adaptation (18%), Functionality Addition (65%)