CourseAI System Design: The Complete Course · Module 2: Requirements · part 15 of 107
Part 15 · Module 2: Requirements

Lesson 2: Setting the quality bar before the design

28 min read·
Module 2 · Lesson 2 · About 45 minutes · Needs: Module 1 lesson 1 (plausible failures) and lesson 1 of this module (problem framing)

The situation

Week 2 at Northdesk, Monday 9 November 2026. Joel has written the requirement for Ask: "answers should be accurate". Helen sends it back. Accurate how often, wrong in which way, and what happens to the employee when it is wrong?

Take one golden question. Olga Quigley, in operations at Marlow County Council, asks "How many days of annual leave do I get?". The 2026 policy says 30; the superseded 2025 policy, still indexed, says 28. This lesson turns "accurate" into four numbers a gate can check.

BEFORE AND AFTER From a wish to four numbers BEFORE answers should be accurate cannot fail a release AFTER: THE QUALITY BAR wrong answers at most 2% unsafe answers none unanswered at most 15% test answers at least 300
"Accurate" cannot fail a release (red, a requirement that protects nobody); four numbers can (blue, Northdesk's bar; green, the limits a gate checks).

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