# Domain Modeling

> 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.

- Skill: `future3ooo/domain-modeling` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add future3ooo/domain-modeling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/future3ooo/domain-modeling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: future3OOO (https://skillmd.com/u/future3ooo)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/future3ooo/domain-modeling

---


# 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 when they crystallize.

Merely reading `CONTEXT.md` for vocabulary is not this skill. That is a one-line habit any skill can follow. Use this skill when changing the model, not just consuming it.

## File Structure

Most repos have a single context:

```text
/
|-- 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:

```text
/
|-- CONTEXT-MAP.md
|-- docs/
|   `-- adr/
`-- src/
    |-- ordering/
    |   |-- CONTEXT.md
    |   `-- docs/adr/
    `-- billing/
        |-- CONTEXT.md
        `-- docs/adr/
```

Create files lazily. 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. Example: "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. Example: "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 precision around concept boundaries.

### Cross-Reference With Code

When the user states how something works, check whether the code agrees. If you find a contradiction, surface it. Example: "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` immediately. Do not batch these up; capture them as they happen. Use the format in [CONTEXT-FORMAT.md](CONTEXT-FORMAT.md).

`CONTEXT.md` should be devoid of implementation details. Do not treat it 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 it works this way.
3. **The result of a real trade-off** - there were genuine alternatives and one was chosen for specific reasons.

If any of the three is missing, skip the ADR. Use the format in [ADR-FORMAT.md](ADR-FORMAT.md).