System Design Card 381 — Data Model / Breakdown
Concern
The data model should fit the access patterns, consistency needs, and entities that matter most. A messaging system may need message records, user preferences, templates, provider receipts, and status history.
What Breakdown means for this concern
In BASIC, the Breakdown step is where you clarify the product goal, workload shape, and non-functional requirement that will dominate the design. For Data Model, 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 split the problem before trying to solve it. 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 miss is treating schema as an afterthought instead of a design core. 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 Breakdown stage, how does Data Model change the architecture, the trade-offs, or the review checklist?”