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In software engineering, the laws of software evolution refer to a series of laws that Lehman and Belady formulated starting in 1974 with respect to software evolution. The laws describe a balance between forces driving new developments on one hand, and forces that slow down progress on the other hand. Over the past decades the laws have been revised and extended several times. ==Context== Observing that most software is subject to change in the course of its existence, the authors set out to determine laws that these changes will typically obey, or must obey in order for the software to survive. In his 1980 article,〔 Lehman qualified the application of such laws by distinguishing between three categories of software: * An ''S''-program is written according to an exact specification of what that program can do * A ''P''-program is written to implement certain procedures that completely determine what the program can do (the example mentioned is a program to play chess) * An ''E''-program is written to perform some real-world activity; how it should behave is strongly linked to the environment in which it runs, and such a program needs to adapt to varying requirements and circumstances in that environment The laws are said to apply only to the last category of systems. 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「Lehman's laws of software evolution」の詳細全文を読む スポンサード リンク
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