Editing Software maintenance (section)

==Categories of software maintenance==
The key purpose of software maintenance is ensuring that the product continues to meet usability requirements. At times, this may mean extending the product's capabilities beyond what was initially envisioned.{{sfn|Varga|2018|p=4}}

According to the [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 14764 specification, software maintenance can be classified into four types:{{sfn|Varga|2018|p=5}}
* [[Corrective maintenance]]: modification of software to fix a [[software bug|bug]] or other failure to meet requirements, typically reported by an end user.{{sfn|Varga|2018|p=5}}{{sfn|Tripathy |Naik|2014|pp=26-27}}
* [[Preventive maintenance]]: forward-looking modification of software after delivery to ensure it continues to meet requirements or fix problems that have not manifested yet.{{sfn|Tripathy |Naik|2014|p=27}}{{sfn|Varga|2018|p=5}} This type of maintenance is performed especially on systems that are required to be highly safe or available.{{sfn|Tripathy |Naik|2014|p=27}} [[Software rejuvenation]] is one form of preventative maintenance to clean up state and prevent future problems.{{sfn|Tripathy |Naik|2014|p=27}}
* Adaptive maintenance: modification of software performed after delivery to ensure its continuing usability in a changed or changing environment.{{sfn|Varga|2018|p=5}}{{sfn|Tripathy |Naik|2014|p=27}}
* Perfective maintenance: enhancement of software after delivery to improve qualities such as [[user experience]], processing efficiency, and [[maintainability]].{{sfn|Tripathy |Naik|2014|p=27}}{{sfn|Varga|2018|pp=5-6}} Perfective maintenance is necessary if other types of maintenance are carried out, because modification of an existing code base will otherwise increase complexity and cause the existing structure to deteriorate.{{sfn|Varga|2018|pp=5-6}} Perfective maintenance may include rewriting [[software documentation|documentation]], [[code refactoring]], and performance tuning.{{sfn|Tripathy |Naik|2014|p=27}}
According to some estimates, enhancement (the latter two categories) comprises some 80 percent of software maintenance.{{sfn|Varga|2018|p=5 fn 4}}