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:

/
|-- 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/
`-- 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.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.