Apply when writing stateful logic, or when code branches a lot or repeats a shape assumption across files. Encode the domain in a structure instead of scattered conditionals.
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What the file says
# Model the Domain
Encode the real domain in a data structure instead of scattering it across conditionals.
**Why:** Scattered booleans, repeated shape assumptions, and branching spread across files are accidental complexity. A structure that matches the domain makes invalid states unrepresentable and deletes branches. Choosing it at write time is cheap. Recovering it later reads as a refactor and gets deferred.
**Reach for structures like these:**
- A state machine instead of scattered booleans, phases, or lifecycle checks.
- A typed object/model instead of loose parameters or repeated shape assumptions.
- A map, registry, lookup table, or discriminated union instead of branching spread across files.
- A reducer or command/event model instead of ad hoc state mutations.
- A module organized around one body of domain knowledge instead of a sequence such as load, validate, transform, and save. Execution order is not ownership.
- A small module boundary that gathers repeated behavior, ownership, or invariants.
- A queue, cache, index, graph/tree, or normalized collection where the data access pattern calls for it.
…
The line at the top of this page pins the label git:20261005.32edae5, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
GET https://markdownregistry.com/api/v1/artifacts/art_4fkjtrm6byzpqgzh
GET https://markdownregistry.com/api/v1/resolve?ref=barbieri/local-openfinance/principle-model-the-domain
GET https://markdownregistry.com/api/v1/blob/bbadbb9a723fac3f76e782ae45665eb94058ec10993e4bae36d4dc6b0e4eac07
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
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