Event Sequence

Chronicle has the concept of event sequences. These can be looked upon as collections of events. Every event gets assigned an incremental unique sequence number, this if the sequence number that observers uses to maintain their offset.

With every event, Chronicle collects additional metadata that is stored together with the event.

Chronicle has formalized the following event sequences:

Type	Description
Event Log	The main sequence you typically append to

Event Type generations

Every event type can evolve over time. Evolutions are represented as generations. The content property stores event content per generation, allowing for a perfect audit trail of the events and its evolution and at the same time also supporting scenarios of delivering different versions of the events, depending on the observer.

Compensations

An event sequence is append only, meaning that we do not delete anything within a sequence. Changing the content of an event is also not supported by Chronicle, instead one should perform compensations.

Compensations are replacements of the original event instance and are in fact the same event type and are stored together with the original event it replaces. Every compensation is stored with the same type of metadata as for the root event.

This approach help us guarantee a perfect audit trail of the system.

Note: Compensations are not fully implemented yet, there is no API surface for it. Internally Chronicle has been prepared for it and that is why you'll see the compensations array on every event.