Nine rules for Requirements

I saw this list on a project in 2002. The rules are still relevant today.

Requirements must be:

• Unambiguous. Has only one possible meaning.
• Correct. Accurately states a customer need.
• Complete. Nothing is missing. No "To Be Determined" (TBD's).
• Consistent. Does not conflict with other requirements.
• Testable. Tests can be devised to demonstrate correct implementation.
• Traceable. Linked to system requirements, designs, code, and tests.
• Modifiable. Can be easily changed (with history) when necessary.
• Necessary. Document something customers really need.
• Prioritized. Ranked by importance.