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A. The Laws of Software Design
This appendix summarizes all of the actual laws discussed in this book:
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The purpose of software is to help people.
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The Equation of Software Design:
where:
- D
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Stands for the desirability of the change.
- Vn
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Stands for value now.
- Vf
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Stands for future value.
- Ei
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Stands for the effort of implementation.
- Em
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Stands for the effort of maintenance.
This is the primary law of software design. As time goes on, this equation reduces to:
Which demonstrates that it is more important to reduce the effort of maintenance than it is to reduce the effort of implementation.
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The Law of Change: The longer your program exists, the more probable it is that any piece of it will have to change.