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Software maintenance in software engineering is the modification of a software product after delivery to correct faults, to improve performance or other attributes. A common perception of maintenance is that it merely involves fixing defects. However, one study indicated that over 80% of maintenance effort is used for non-corrective actions.〔Pigoski, Thomas M., 1997: Practical software maintenance: Best practices for managing your software investment. Wiley Computer Pub. (New York)〕 This perception is perpetuated by users submitting problem reports that in reality are functionality enhancements to the system. More recent studies put the bug-fixing proportion closer to 21%.〔Eick, S., Graves, T., Karr, A., Marron, J., and Mockus, A. 2001. Does Code Decay? Assessing Evidence from Change Management Data. IEEE Transactions on Software Engineering. 27(1) 1-12.〕 ==History== Software maintenance and evolution of systems was first addressed by Meir M. Lehman in 1969. Over a period of twenty years, his research led to the formulation of Lehman's Laws (Lehman 1997). Key findings of his research include that maintenance is really evolutionary development and that maintenance decisions are aided by understanding what happens to systems (and software) over time. Lehman demonstrated that systems continue to evolve over time. As they evolve, they grow more complex unless some action such as code refactoring is taken to reduce the complexity. In the late 1970s, a famous and widely cited survey study by Lientz and Swanson, exposed the very high fraction of life-cycle costs that were being expended on maintenance. They categorized maintenance activities into four classes: * Adaptive – modifying the system to cope with changes in the software environment (DBMS, OS) 〔(''Software Maintenance and Re-engineering'' ), CSE2305 Object-Oriented Software Engineering〕 * Perfective – implementing new or changed user requirements which concern functional enhancements to the software * Corrective – diagnosing and fixing errors, possibly ones found by users 〔 * Preventive – increasing software maintainability or reliability to prevent problems in the future 〔 The survey showed that around 75% of the maintenance effort was on the first two types, and error correction consumed about 21%. Many subsequent studies suggest a similar magnitude of the problem. Studies show that contribution of end user is crucial during the new requirement data gathering and analysis. And this is the main cause of any problem during software evolution and maintenance. So software maintenance is important because it consumes a large part of the overall lifecycle costs and also the inability to change software quickly and reliably means that business opportunities are lost. 〔Lientz B., Swanson E., 1980: Software Maintenance Management. Addison Wesley, Reading, MA〕 〔Lehman M. M., 1980: Program, Life-Cycles and the Laws of Software Evolution. In Proceedings of IEEE, 68, 9,1060-1076〕 〔Penny Grubb, Armstrong A. Takang, 2003: Software Maintenance: Concepts and Practice. World Scientific Publishing Company〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Software maintenance」の詳細全文を読む スポンサード リンク
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