05. Extract business rules

What it is

Turn prose into invariants: bounds, ownership, valid states, currency, duplicate behavior.

When to use it

Workflow step 5 of 17. Apply before moving to the next decision.

Syntax

5. Extract business rules
Turn prose into invariants: bounds, ownership, valid states, currency, duplicate behavior.

Example

Amount must be positive.
Source/destination must differ.
Currencies must match.
An already settled transfer cannot settle twice.

Common mistakes

Skipping this decision makes later implementation depend on unstated assumptions.

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