Events

Events are facts that happened and are of interest to the software system. In principal, anythings that is detected by the software system is an event. Events can be detected from outside of the system, for example:

• User selected a product
• Third-party service sent an API request Events can be detected from within the system, for example:
• Free trial period ended
• User credit score updated As you can see, all the example are phrased in a past tense. This is because events are things that have already happened.

Event Structure

In Eventualize, All events have the same structure:

property name	data type	meaning
event_type	string	required. A description of the event (e.g. “user earned points”)
captured_at	datetime	required. The point in time in which the event was detected
captured_by	string	required. The name of the service that detected the event
payload	json	required. The data of the event (e.g. username, number of points)
stored_at	datetime	Optional. Populated by Eventualize after the event has been stored

Now that we understand events, we can learn how they are used to derive the system’s state. Hint: this is what Aggregates are for. Let’s proceed to the Aggregates section!