The DCB Tag Dilemma
The “crazy wall” in the 2001 film A Beautiful Mind DCB introduces tags as a consistency mechanism to identify the events required to enforce the consistency constraints. Along with the event type, tags are one of the two key attributes you can use to filter events relevant to a specific decision. Type and tag describe two different sides of the same event—two complementary dimensions. Used together, they let you define very precisely which events you need to consider to make a particular decision. Let’s unpack what each dimension means. Event type: what happened An event’s type describes the nature of the fact itself: what happened. “StudentSubscribedToCourse” is a typical event type. It doesn’t tell you who was involved or provide any context. It only conveys the kind of thing that occurred, describing the fact without tying it to the specific entities involved. The type is also semantically tied to the business logic used to process the event. It’s easy to see why:...