Domains

A Domain is a subject area of the Product (ordering, catalog, billing) that groups the Capabilities and Entities about it. It follows the sections the Product itself shows people, and it classifies without containing: nothing moves into a Domain's folder.

In practice

In the fixture shop, six Capabilities and five Entities, such as Order and Refund, name ordering. browse-catalog names no Domain.

When you create one

One Domain per section of the Product's navigation, settings or administration that holds two or more Capabilities, named the way the Product names that section. A Product with no such section has no Domains, and that is valid.

• Use the finest section that still holds two. Settings with Billing and Team pages, each holding several Capabilities, is two Domains, not one Settings Domain.
• Something several sections reach has no Domain, and nothing that is not a section becomes one. A Capability alone on a page beside a sibling section has no Domain either.
• Something no section reaches (signing in, a link in an email, a scheduled job) joins the one section whose Capabilities change the same Entities, or has no Domain.
• Splitting a Capability never changes the Domains. If manage-orders became four Capabilities, they share a Domain only if the Product's sections say so.
• An author's Domains are kept. Once someone has written or regrouped Domains, mapping adds new Capabilities to them and never re-cuts, merges or renames them.

Team ownership, compliance concerns or code structure never make a Domain; the model describes the Product, not the organization building it.

The file

domains/<id>.md. The H1 names the Domain, the lead says what it is about, and ## Boundary says what it covers and what it does not.

---
colorSlot: 4
---

# Ordering

Everything between a full cart and a fulfilled order.

## Boundary

Owns cart contents, order state, and the transition between them. It does not
own catalog information or fulfilment logistics.

How it connects

Only two resources name a Domain, each with an optional single domain: (a Capability and an Entity). Everything else follows from those: a Screen or Journey is about the Domains of the Capabilities it uses. So one Domain gathers everything about its subject across the model.

A Domain is what a part of the Product is about; a Capability is something it can do. Where a Capability can be reached is its availability, not its Domain.

What lint checks

Errors:

• A missing H1, lead paragraph or ## Boundary.
• A ## Boundary that never says what the Domain does not own.
• A Capability or Entity naming a Domain that has no file.

Warnings:

• A Domain named by fewer than two Capabilities: it is a folder, not a region. Entities don't count.
• A Domain id that opens with a verb acting on something the model declares.