Event Driven Development

Event Notification happens when a system sends event messages to notify other systems of a change in its domain

In event notification the source system must always get an answer for the notification.

The problem with event notification emerges when a logical flow runs over various event notifications because it can be hard to see the flow from the program text

An event must carry all the data on needed for the receiver to decide what to do next.

Event-Carried State Transfer pattern involves more complexity on the receiver

The best example of Event-Sourcing is a version-control system

There is no need for a clear separation between domain processing and deriving a working copy from the event log.