Events

Events are immutable, past-tense facts — the record of something that happened. An event declaration defines the event type’s name and properties. Properties use concepts or primitives.

Syntax

event <Name>
  <property> <Type>
  ...

Example

event InvoiceRegistered
  invoiceId     InvoiceId
  customerId    CustomerId
  invoiceNumber InvoiceNumber
  lines         InvoiceLine[]
  currency      CurrencyCode
  registeredAt  DateTime
  status        InvoiceStatus

Type modifiers

Modifier	Syntax	Example
Collection	<Type>[]	lines InvoiceLine[]
Optional	<Type>?	note String?

Guidance

• Name events in the past tense and make them self-describing: InvoiceRegistered, never Created.
• One purpose per event. If an event needs a nullable property to cover two situations, model the second situation as its own event.
• Compliance is inherited. A property typed with a @pii concept is PII — nothing extra to declare on the event.
• The event-source identity is not an event property; it travels in the event context. Commands bind it when they produce events.