For the event sourcing pattern to work, all changes to an object’s state should be rep‐ resented and persisted as events. These events become the system’s source of truth (hence the name of the pattern). This process is shown in Figure 7-1.

Figure 7-1. Event-sourced aggregate

The database that stores the system’s events is the only strongly consistent storage: the system’s source of truth. The accepted name for the database that is used for persist‐ ing events is event store.