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.
