Don't Repeat Yourself (DRY) Or Once And Only Once (O3)


Don't Repeat Yourself (DRY, also known as Single Point of Truth) is a process philosophy aimed at reducing duplication, particularly in computing. The philosophy emphasizes that information should not be duplicated, because duplication increases the difficulty of change, may decrease clarity, and leads to opportunities for inconsistency. DRY is a core principle of Andy Hunt and Dave Thomas's book The Pragmatic Programmer. They apply it quite broadly to include "database schemas, test plans, the build system, even documentation."[1] When the DRY principle is applied successfully, a modification of any single element of a system does not change other logically-unrelated elements. Additionally, elements that are logically related all change predictably and uniformly, and are thus kept in sync.

avoid multiple and possibly diverging ways to express every piece of knowledge

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