Clear requirement text matters

Abstract

Many “How to Write Good Requirements” guidelines seek to prevent programs from overrunning, being mired in delays, or suffering a flight catastrophe. It is rare, however, to see concrete examples that unambiguously shed light on why these best practices are necessary.This paper cites several space mission mishaps to emphasize a need for clear requirement text preparation. It explores three common genres of flaws with the text of requirements: numbers that do not have well-defined units or tolerance ranges, clauses that are ambiguous in their intention, and statements that lump multiple requirements together.Government and industry guidance rail against these three kinds of text flaws and prescribe rules to catch them. Yet poorly worded requirements still occur routinely, likely because most authors do not realize how faulty text can have severe consequences. By recounting past failures, the authors hope to motivate the readers into heeding simple, if mundane, rules and thus be spared from the unpleasant consequences of ill-written requirements.