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A good requirement states something that is necessary, verifiable, and attainable.

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Even if it is verifiable and attainable, and eloquently written, if it is not necessary, it is not a good requirement. To be verifiable, the requirement must state something that can be verified by examination, analysis, test, or demonstration. Statements that are subjective, or that contain subjective words, such as "easy", are not verifiable. If a requirement is not attainable, there is little point in writing it. A good requirement should be clearly stated.

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Need. If there is a doubt about the necessity of a requirement, then ask: What is the worst thing that could happen if this requirement were not included? If you do not find an answer of any consequence, then you probably do not need the requirement.

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Verification. As you write a requirement, determine how you will verify it. Determine the criteria for acceptance. This step will help insure that the requirement is verifiable.

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Attainable. To be attainable, the requirement must be technically feasible and fit within budget, schedule, and other constraints. If you are uncertain about whether a requirement is technically feasible, then you will need to conduct the research or studies to determine its feasibility. If still uncertain, then you may need to state what you want as a goal, not as a requirement. Even if a requirement is technically feasible, it may not be attainable due to budget, schedule, or other, e.g., weight, constraints. There is no point in writing a requirement for something you cannot afford -- be reasonable.

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Clarity. Each requirement should express a single thought, be concise, and simple. It is important that the requirement not be misunderstood -- it must be unambiguous. Simple sentences will most often suffice for a good requirement.

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