domain-modeling

Files (4)

• SKILL.md
• openai.yaml · agents/
• ADR-FORMAT.md · references/
• GLOSSARY-FORMAT.md · references/

SKILL.md (first lines)

# Domain Modeling

Actively build and sharpen the project's domain model as you design. This is the _active_ discipline — challenging terms, inventing edge-case scenarios, and writing the glossary and decisions down the moment they crystallise. (Merely _reading_ `GLOSSARY.md` for vocabulary is not this skill — that's a one-line habit any skill can do. This skill is for when you're changing the model, not just consuming it.)

## File structure

Most repos have a single context:

```
/
├── GLOSSARY.md
├── docs/
│   └── adr/
│       ├── 0001-event-sourced-orders.md
│       └── 0002-postgres-for-write-model.md
└── src/
```

If a `GLOSSARY-MAP.md` exists at the root, the repo has multiple contexts. The map points to where each one lives:

```
/
├── GLOSSARY-MAP.md
├── docs/
│   └── adr/                          ← system-wide decisions
├── src/
│   ├── ordering/
│   ├── GLOSSARY.md
│   │   └── docs/adr/                 ← context-specific decisions
│   └── billing/
│   ├── GLOSSARY.md
│       └── docs/adr/
```

Create files lazily — only when you have something to write. If no `GLOSSARY.md` exists, create one when the first term is resolved. If no `docs/adr/` exists, create it when the first ADR is needed.

## During the session

### Challenge against the glossary

When the user uses a term that conflicts with the existing language in `GLOSSARY.md`, call it out immediately. "Your glossary defines 'cancellation' as X, but you seem to mean Y — which is it?"

### Sharpen fuzzy language

When the user uses vague or overloaded terms, propose a precise canonical term. "You're saying 'account' — do you mean the Customer or the User? Those are different things."

### Discuss concrete scenarios

When domain relationships are being discussed, stress-test them with specific scenarios. Invent scenarios that probe edge cases and force the user to be precise about the boundaries between concepts.

### Cross-reference with code

When the user states how something works, check whether the code agrees. If you find a contradiction, surface it: "Your code cancels entire Orders, but you just said partial cancellation is possible — which is right?"

### Update GLOSSARY.md inline

When a term is resolved, update `GLOSSARY.md` right there. Don't batch these up — capture them as they happen. Use the format in [GLOSSARY-FORMAT.md](./references/GLOSSARY-FORMAT.md).

`GLOSSARY.md` should be totally devoid of implementation details. Do not treat `GLOSSARY.md` as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary and nothing else.

### Offer ADRs sparingly

Only offer to create an ADR when all three are true:

1. **Hard to reverse** — the cost of changing your mind later is meaningful
2. **Surprising without context** — a future reader will wonder "why did they do it this way?"
3. **The result of a real trade-off** — there were genuine alternatives and you picked one for specific reasons

If any of the three is missing, skip the ADR. Use the format in [ADR-FORMAT.md](./references/ADR-FORMAT.md) (Simple vs Formal ADRs). When creating a Formal ADR with `deciders:` frontmatter, default to the user's local GitHub username (via `gh api user --jq .login` or `git config user.name`), never generic (`Team`) or AI names. For managing system-wide ADRs, RFCs, Design Specs, or running automated ADR validation, reach for the [`docs`](../../productivity/docs/SKILL.md) skill (`bun run skills/productivity/docs/scripts/validate-adrs.mjs`).

From ngxccc/engineered-skills, MIT.

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