# Domain Modeling
Actively 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 . (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, .)
## 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/
```
: 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`, . "Your glossary defines 'cancellation' as X, but you seem to mean Y. Which is it?"
### Sharpen fuzzy language
When the user uses , propose . "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, with specific scenarios. Invent scenarios that and force the user to be precise about the boundaries between concepts.
###
When the user states how something works, check whether the code agrees. If you find a contradiction, : "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. : capture them as they happen. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md).
`CONTEXT.md` should be . Do not treat `CONTEXT.md` as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary and nothing else.
###
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. ****: 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).