Functional vs Non-Functional Requirements Lab (Interactive)
Pick core flows, quantify SLOs, declare non-goals, and score your minute-zero scope contract. Choose the Rule-of-3 functional flows for a Twitter, Uber, YouTube, or TinyURL prompt, set availability, latency, and ratio targets, and see the scope-creep penalty update live.
Requirements Scoping Contract
Propose a Rule-of-3 scope, quantify NFR physics, declare non-goals, and score your minute-0 contract.
Functional scope (click to include)
Non-functional physics
Social timelines tolerate 1-2s eventual consistency to protect 99.99% availability and sub-100ms reads.
The Passive Trap: scope too thin, interviewer will pile on features
How It Works Under the Hood
The first five minutes decide the interview. Senior candidates propose a crisp contract - exactly two to three functional flows spanning the write, read, and interaction archetypes; quantitative non-functional SLOs like p99 latency and availability nines with their real downtime minutes; and explicit out-of-scope non-goals. This lab scores the contract: tangential features like Direct Messaging earn negative points inside scope and positive points when declared as non-goals, while the CAP choice must match the workload physics - AP for social feeds, CP for ride fare and booking flows - or alignment fails.
Core Architectural Principles
- Rule of 3: 2-3 core flows covering write, read, and interaction archetypes score; extras trigger scope-creep penalties.
- Availability nines convert to concrete downtime per year so the SLO is quantitative, not a buzzword.
- CAP alignment: the AP/CP choice must match the prompt workload, and non-goals must be declared explicitly.
Propose, never interrogate. Deliver a sixty-second pitch naming three flows, three quantified SLOs, and three non-goals, then close with "Does this scope align with what you would like to evaluate?" Say the CAP choice out loud - prioritizing Availability with eventual consistency for timelines signals production judgment and locks in evaluation criteria before you draw a single box.
A tight scope protects the time budget and shows product sense, but scoping too narrow invites the interviewer to pile on features mid-session.