Derive Nfr From Driver

Derive NFR From Driver

Turns a ratified business driver (BR) — and the functional requirements (FRs) derived from it — into measurable Non-Functional Requirements with verified parentage. This skill does NOT elicit drivers and does NOT invent FRs; it derives NFRs against parents that already exist on disk.

When to Use

• A BR-* and at least one FR-* exist for the engagement and need performance, availability, scalability, or accessibility targets before Phase D begins.
• The architect is about to design components and needs SLO-shaped inputs, not adjectives.
• A reviewer asks "what does fast mean?" — derive an NFR with a numeric target instead of arguing prose.
• NOT when the driver itself is unratified — go to requirements-elicitation first.

Prerequisites

• requirements/<engagement>/BR/ contains at least one ratified BR-* artifact (ratified_by is non-empty).
• requirements/<engagement>/FR/ contains the FR(s) this NFR will constrain.
• spec/artifact-schema.md is the contract for frontmatter fields.

If a prerequisite is missing the skill must stop and report — never emit an NFR pointing at a non-existent or unratified parent.

How to Run

# 1. Confirm the parent exists and is ratified
bash scripts/verify-traceability.sh requirements/<engagement>

# 2. Create the NFR file (filename MUST equal {id}.md)
#    Then run the gate again to prove the new link resolves
bash scripts/verify-traceability.sh requirements/<engagement>

Quick Reference

The frontmatter the agent emits:

---
id: NFR-007
layer: NFR
title: Classification latency under load
parent_ids: [BR-001, FR-002]
owner: jane.doe@example.com
measurable: true
ratified_by: ""
target: "p95 < 2s on 3G, p99 < 4s"
derivation_skill: derive-nfr-from-driver
tags: [latency, classification]
---

Procedure

Step 1: Assess

• Read the parent BR-* and any candidate FR-* with view.
• Identify the quality attribute the driver implies: latency, throughput, availability, durability, accessibility, recoverability, observability, portability.
• Reject the derivation outright if the driver is unratified (ratified_by empty). Send back to requirements-elicitation.

Step 2: Derive

For each quality attribute, write one NFR with:

• A numeric target in the target field (percentile + threshold + operating envelope — never just "fast"). If you cannot write a number, you have not derived an NFR yet.
• A measurement method stated in the body (synthetic probe, RUM, load test fixture). Without it the NFR is unfalsifiable.
• An operating envelope: load profile, network condition, payload size. NFRs without envelopes drift on contact with production.

Step 3: Link

• parent_ids MUST include the driver's BR-* and SHOULD include the most specific FR-* the NFR constrains.
• derivation_skill: derive-nfr-from-driver is mandatory — the curator uses this to attribute learned patterns.

Step 4: Confirm

bash scripts/verify-traceability.sh requirements/<engagement>

The gate must pass with zero failures. A warning on ratified_by is expected until a human ratifies the NFR at the architecture review board.

Pitfalls

• DO NOT invent a parent BR to justify an NFR you already wanted — the skill exists specifically to prevent this. If the parent does not exist, stop.
• DO NOT write measurable: false to bypass the gate; the gate fails on it for NFRs by design (see spec/artifact-schema.md §2.3).
• DO NOT parent an NFR to another NFR — the schema disallows it. NFRs are leaves of the requirement layer, not branches.
• DO NOT set ratified_by from inside the agent. Ratification is the human's signal that the derivation is accepted. The agent leaves it blank.
• DO NOT copy the driver's prose into the target field. The target is a number with units; the prose belongs in the body.

Verification

• New NFR-*.md filename equals its id.
• parent_ids lists at least one BR-* that exists on disk.
• target contains a numeric threshold and an operating envelope.
• bash scripts/verify-traceability.sh requirements/<engagement> exits 0.
• bash scripts/gen-rtm.sh requirements/<engagement> shows the new NFR linked under its driver in docs/rtm.md.
• bash scripts/verify.sh passes the full gate.