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 the moment they crystallise. (Merely reading the knowledge bundle's glossary 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

The domain model lives in an Open Knowledge Format (OKF) knowledge bundle at knowledge/ in the repo root. Most repos have a single context:

knowledge/
├── index.md              ← bundle map (reserved: no frontmatter)
├── log.md                ← change history, newest first (reserved: no frontmatter)
├── glossary/             ← one file per term (the glossary)
│   ├── index.md
│   ├── order.md
│   └── customer.md
└── adr/                  ← one file per decision
    ├── index.md
    ├── adr-0001-event-sourced-orders.md
    └── adr-0002-postgres-for-write-model.md

For multiple bounded contexts, each context is a subdirectory inside the one bundle (knowledge/ordering/glossary/, knowledge/billing/glossary/, …) and knowledge/index.md is the context map. See [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md).

Create files lazily — only when you have something to write. If no knowledge/glossary/ exists, create it when the first term is resolved. If no knowledge/adr/ exists, create it when the first ADR is needed. Whenever knowledge changes, update the concept AND append to knowledge/log.md.

Extending the bundle (new concept categories)

glossary/ and adr/ are the two categories every bundle has; spec/ (written by /to-spec) is the third canonical one. But OKF is an open format — type is a free field and the bundle is not limited to a fixed set of folders. When you meet a durable domain entity that genuinely fits none of them — a recurring kind of thing the project needs recorded in its own right — a new concept category is legitimate.

Don't spin one up silently. When you judge a new category is warranted:

1. Propose it — name the category, say what kind of entity it holds and why glossary/adr/prd don't fit.
2. Get the user's sanction before creating the directory.
3. Register it in knowledge/index.md (and give it an index.md like every other category) so the bundle map stays honest.

Default to the existing three. A new category is the exception, not the reflex.

During the session

Challenge against the glossary

When the user uses a term that conflicts with the existing language in the glossary, 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 the glossary inline

When a term is resolved, write it to knowledge/glossary/ right there. Don't batch these up — capture them as they happen. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md).

The glossary should be totally 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 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).

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: evist0
• Source: evist0/okf-matt-skills
• License: MIT

Install and usage instructions live in the source repository linked above.