Reference

• Commands (intent)
• Procedures (pure business logic)
• Events (immutable facts)
• Policies (reconciliation logic)
• Queries (read operations)
• Mutations (write operations)

Events

• Must described in past-tense
• Must be Immutable
• Should be self contained (all data required for representing some model state is contained in events)
• Ordered

Commands

• Represent an intention or request to perform an action
• MUST be serializable (JSON, YAML, etc.)
• MUST be immutable
• Named in imperative form (e.g., ScanPartition, InspectStorage)
• MUST NOT contain business logic or behavior
• Self-contained with all required data for execution

Procedures

• Consume Commands
• CAN emit Events
• CAN query state (read-only)
• MUST NOT mutate state
• Have signature: (context: ProcedureContext, command: Command) -> None
• Stateless (all state via context or command)
• Contain business logic for processing commands

Policies

• Consume Events
• CAN emit Commands
• CAN query state (read-only)
• CAN mutate state (via mutations)
• Have signature: (context: PolicyContext, event: Event) -> None
• Stateless (all state via context or event)
• Contain business logic for reacting to events

Models

Queriers

• Perform read-only operations
• MUST NOT mutate state
• MUST NOT emit events or commands
• Have signature: (input: QueryInput) -> QueryResult
• Deterministic when possible
• CAN access external systems (databases, filesystems, APIs)
• Return serializable data structures

Mutators

• Perform write operations
• CAN mutate state (event store, databases, filesystems, etc.)
• MUST NOT emit events or commands directly
• Have signature: (input: MutationInput) -> MutationResult
• Idempotent when possible
• CAN have side effects
• Return confirmation or status of the mutation