5. Corrective maintenance

Most systems have imperfections. The initial testing of the system should find many of them but more obscure errors may only be encountered as users interact with the system day after day.

Part of the system should include a way for customers / users to report these problems. Also error logs should be included in the system so maintenance staff can spot problems even if they are not reported.

Software / programming errors

Almost all commercial software systems seem to need fixing even after they have been released.

Software code can be very complex so even the most diligent test regime fails to find all of the errors.

The way these are fixed is often in the form of a software patch that the user downloads or it is sent to their computer by the IT staff over the company network..

Another common corrective maintenance action is to fix security vulnerabilities in the code. Again, the usual way of doing this is by software patch.

Logical or business process errors

This is where the system is not behaving in the way it was intended, not because of a programming error but because the coder misunderstood what was needed to support the business in the first place.

For example, a database may be storing data in such a way that it is causing problems for other systems within the company. These types of errors may be much harder to fix compared to straight forward programming errors because they may be a fundamental part of the system.

This is why a robust requirements document is needed to avoid logical and business process errors.