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SPM: Single Point of Maintenance

The task of a maintenance programmer is to implement a requested change to a piece of software in a consistent fashion, for example, a change to the calculation of sales tax affecting multiple programs.

This task is made unnecessarily difficult if the program is constructed in such a way that algorithms and values are duplicated throughout the code, for example through the use of copy and paste, or by hard-coding values into a program.

The concept of a single point of maintenance dictates that frequently used elements should be defined, and modified, in a single location. Duplication of such elements increases the difficulty of change, may decrease clarity and increases the likelihood of inconsistency.

There are three contraventions of Single Point of Maintenance that are easy to detect: