domain-modeling

Files (4)

• ADR-FORMAT.md
• CONTEXT-FORMAT.md
• GLOSSARY-FORMAT.md
• SKILL.md

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* `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.)

## File structure

Most repos have a single context:

```
/.agents/docs/
├── CONTEXT.md
├── ADR-LIST.md
```

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

```
/.agents/docs/
├── CONTEXT-MAP.md
├── GLOSSARY.md                         ← project-wide ubiquitous language
├── ADR-LIST.md                         ← system-wide decisions
├── ordering/
│   ├── CONTEXT.md
│   └── ADR-LIST.md                     ← context-specific decisions
└── billing/
    ├── CONTEXT.md
    └── ADR-LIST.md
```

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 `GLOSSARY.md` exists, create it when the first cross-context term is resolved. If no `ADR-LIST.md` 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.

### Maintain the root GLOSSARY.md

The root `GLOSSARY.md` (next to `CONTEXT-MAP.md`) holds the project-wide ubiquitous language: terms used across more than one context. A term belongs there when it is shared kernel, a shared handle, or ambiguous across contexts (e.g. `Order`, `Contract`, `Price`, `CustomerNumber`); a term used in exactly one context belongs in that context's `CONTEXT.md`. Each term has exactly one home: once a term is in `GLOSSARY.md`, use it everywhere, including inside `CONTEXT.md` definitions; never redefine it per context. Follow [GLOSSARY-FORMAT.md](GLOSSARY-FORMAT.md). Create it lazily with the first cross-context term and update in place as language sharpens.

### 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).

From Jeroen-G/skills, MIT.

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