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Software maintenance is the modification of software after delivery.[1]
As per the IEEE standard glossary of software engineering terminology, software maintenance refers to the process of modifying and updating software after its initial development and deployment, to correct faults, improve performance or other attributes, add new features to meet evolving user requirements, or adapt to a changed environment. It is important to emphasize that software maintenance thus involves many activities that go beyond mere bug fixing. Software maintenance is an ongoing process that is essential for the longevity of a software system, to keep it effective, adaptable and relevant in an ever-evolving technological landscape.
Software maintenance is often considered lower skilled and less rewarding than new development. As such, it is a common target for outsourcing or offshoring. Usually, the team developing the software is different from those who will be maintaining it. The developers lack an incentive to write the code to be easily maintained. Software is often delivered incomplete and almost always contains some bugs that the maintenance team must fix. Software maintenance often initially includes the development of new functionality, but as the product nears the end of its lifespan, maintenance is reduced to the bare minimum and then cut off entirely before the product is withdrawn.
Each maintenance cycle begins with a change request typically originating from an end user. That request is evaluated and if it is decided to implement it, the programmer studies the existing code to understand how it works before implementing the change. Testing to make sure the existing functionality is retained and the desired new functionality is added often comprises the majority of the maintenance cost.
Software maintenance is not as well studied as other phases of the software life cycle, despite comprising the majority of costs. Understanding has not changed significantly since the 1980s. Software maintenance can be categorized into several types depending on whether it is preventive or reactive and whether it is seeking to add functionality or preserve existing functionality, the latter typically in the face of a changed environment.