System Design Card 358 — Requirements Clarification / Structure
Concern
Every design starts with defining what must be true for the system to be considered successful. A notification system for security alerts is a different system from a marketing fanout service even if both 'send messages'.
What Structure means for this concern
In BASIC, the Structure step is where you turn the chosen trade-offs into a clear high-level architecture and request flow. For Requirements Clarification, that means the candidate should make this concern visible at the right moment instead of bolting it on at the end.
Design move
A good move is to make the plan visible before full execution. Tie the concern back to the user flow, the workload, and the dominant trade-off. That keeps the design grounded and makes it easier for the interviewer to follow why a cache, queue, replica, partition, or rate limiter is actually necessary.
Common miss
The common miss is skipping functional and non-functional requirements and drawing architecture into a vacuum. BASIC helps because the staged flow keeps this concern proportional to the prompt and connected to the rest of the architecture.
BASIC prompt
“When I reach the Structure stage, how does Requirements Clarification change the architecture, the trade-offs, or the review checklist?”