|
| 1 | +--- |
| 2 | +name: domain-modeling |
| 3 | +description: Build and sharpen a project's domain model. Use when the user wants to pin down domain terminology or a ubiquitous language, record an architectural decision, or when another skill needs to maintain the domain model. |
| 4 | +--- |
| 5 | + |
| 6 | +# Domain Modeling |
| 7 | + |
| 8 | +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* `CONTEXT.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.) |
| 9 | + |
| 10 | +## File structure |
| 11 | + |
| 12 | +Most repos have a single context: |
| 13 | + |
| 14 | +``` |
| 15 | +/ |
| 16 | +├── CONTEXT.md |
| 17 | +├── docs/ |
| 18 | +│ └── adr/ |
| 19 | +│ ├── 0001-event-sourced-orders.md |
| 20 | +│ └── 0002-postgres-for-write-model.md |
| 21 | +└── src/ |
| 22 | +``` |
| 23 | + |
| 24 | +If a `CONTEXT-MAP.md` exists at the root, the repo has multiple contexts. The map points to where each one lives: |
| 25 | + |
| 26 | +``` |
| 27 | +/ |
| 28 | +├── CONTEXT-MAP.md |
| 29 | +├── docs/ |
| 30 | +│ └── adr/ ← system-wide decisions |
| 31 | +├── src/ |
| 32 | +│ ├── ordering/ |
| 33 | +│ │ ├── CONTEXT.md |
| 34 | +│ │ └── docs/adr/ ← context-specific decisions |
| 35 | +│ └── billing/ |
| 36 | +│ ├── CONTEXT.md |
| 37 | +│ └── docs/adr/ |
| 38 | +``` |
| 39 | + |
| 40 | +Create files lazily — only when you have something to write. If no `CONTEXT.md` exists, create one when the first term is resolved. If no `docs/adr/` exists, create it when the first ADR is needed. |
| 41 | + |
| 42 | +## During the session |
| 43 | + |
| 44 | +### Challenge against the glossary |
| 45 | + |
| 46 | +When the user uses a term that conflicts with the existing language in `CONTEXT.md`, call it out immediately. "Your glossary defines 'cancellation' as X, but you seem to mean Y — which is it?" |
| 47 | + |
| 48 | +### Sharpen fuzzy language |
| 49 | + |
| 50 | +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." |
| 51 | + |
| 52 | +### Discuss concrete scenarios |
| 53 | + |
| 54 | +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. |
| 55 | + |
| 56 | +### Cross-reference with code |
| 57 | + |
| 58 | +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?" |
| 59 | + |
| 60 | +### Update CONTEXT.md inline |
| 61 | + |
| 62 | +When a term is resolved, update `CONTEXT.md` right there. Don't batch these up — capture them as they happen. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md). |
| 63 | + |
| 64 | +`CONTEXT.md` should be totally devoid of implementation details. Do not treat `CONTEXT.md` as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary and nothing else. |
| 65 | + |
| 66 | +### Offer ADRs sparingly |
| 67 | + |
| 68 | +Only offer to create an ADR when all three are true: |
| 69 | + |
| 70 | +1. **Hard to reverse** — the cost of changing your mind later is meaningful |
| 71 | +2. **Surprising without context** — a future reader will wonder "why did they do it this way?" |
| 72 | +3. **The result of a real trade-off** — there were genuine alternatives and you picked one for specific reasons |
| 73 | + |
| 74 | +If any of the three is missing, skip the ADR. Use the format in [ADR-FORMAT.md](./ADR-FORMAT.md). |
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