90-90 rule

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The 90-90 rule (literally from English ninety-ninety rule ) is an aphorism from software development . He humorously sums up different phenomena of software programming , especially time management during the development phase. The author of the rule is Tom Cargill of Bell Laboratories . She became known in 1985 when Jon Bentley cited her in his column Programming pearls of the Communications of the ACM magazine under the title Rule of Credibility . It is:

"The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time. "

“The first 90 percent of the code takes the first 90 percent of development time. The remaining 10 percent of the code requires the other 90 percent of the development time. "

- Tom Cargill, Bell Laboratories

statement

The wording of the 90-90 rule is reminiscent of the Pareto principle , but, in contrast to it, it is not meant very seriously: the fact that the percentage sum of the development time is more than 100% is an allusion to the time lag that often occurs in software projects is observed. Scheduled deadlines are sometimes postponed several times or simply not adhered to, which is why the actual development time of software often takes significantly longer (180%) than the originally planned period (100%).

The rule also describes the lack of skill in identifying complicated codes when the effort is being estimated. If during the first 90% of the planned project duration the time and the amount of code still match, while working on the last 10% of the code it becomes apparent that the same amount of time is needed for this as for the first 90%, because the effort involved was completely underestimated.

In agile software development , the rule often applies to tasks that are considered "almost finished". Often times, this widespread condition indicates that while the planned work has essentially been completed, the task cannot be marked as complete because it is still waiting for other activity. However, it may still be a long time to come to completion.

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  1. ^ Jon Bentley: Programming pearls: Bumper-Sticker Computer Science . (fee required) In: Communications of the ACM . 28, No. 9, 1985, ISSN  0001-0782 , pp. 896-901. doi : 10.1145 / 4284.315122 .