# Domain Modeling

> Build and sharpen a project's domain model. Use when the user wants to pin down domain terminology or a ubiquitous language boundary.

- Skill: `quantumquirkxyz/domain-modeling` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add quantumquirkxyz/domain-modeling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/quantumquirkxyz/domain-modeling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: quantumquirkxyz (https://skillmd.com/u/quantumquirkxyz)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/quantumquirkxyz/domain-modeling

---


## Contract

- **Input:** problem or task defined by the skill body.
- **Output:** Markdown artifact or structured result with completion criteria met.
- **Side effects:** none (design/review/documentation only unless explicitly stated).
- **Dependencies:** none (self-contained unless linked to other skills).
- **Stop condition:** all process steps completed; artifact saved; criteria checked.
- **Risk:** low.
- **Boundary:** produces reasoning or documentation artifacts; does not modify external systems unless explicitly instructed.


# 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* `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.)

## Contract

- Input: one overloaded or uncertain term, the current codebase context, and the existing glossary.
- Output: one resolved term, or one ADR-ready decision with the glossary updated to match.
- Scope: change the model, not the implementation.
- Rule: if the term is still ambiguous after challenge, say so and keep it unresolved.
- Rule: only propose an ADR when the decision is hard to reverse, surprising, and the result of a real trade-off.

## File structure

Most repos have a single context:

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

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

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

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.

## During the session

### Challenge against the glossary

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?"

### 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 CONTEXT.md inline

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).

`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.

### 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](./ADR-FORMAT.md).

## Completion criteria

- the term has a canonical meaning or is explicitly left unresolved
- the glossary reflects the resolved meaning without implementation detail
- any ADR candidate is either drafted or consciously skipped
- edge cases that affect the meaning are recorded clearly