Software development plans are often incomplete and inaccurate. During the 27 years when I worked at IBM, we once needed a critical new function for the OS/360 programming system. The engineering estimate was $175,000. Naively, that is all the funding I requested. Some months later, the developers found that the work would cost $525,000. They had omitted many necessary tasks from their original plan. They had forgotten documentation; testing; the integration, build, and release processes; and quality assurance. Sure enough, however, the coding and unit test costs were about $175,000. They had made a pretty good estimate, but their plan was painfully (for me) incomplete. I had to make up the difference out of department funds.

The problem ...

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