Sometimes, processes don’t unfold according to expectations. That’s where escalation and error events are useful.

Consider the case of a journey by train. The journey can proceed in one of three ways:

  • The journey can be completed on schedule (the happy path).
  • The journey can be completed after a delay.
  • The journey can be canceled.

The Happy Path

Here’s how the happy path (highlighted in green) might be modeled.

The “happy path” of a train journey

Train Delayed

If there is a delay,

  • A throwing escalation intermediate event triggers the Inform customer task.
  • The journey is completed after the delay.

The yellow highlights indicate the process flow in this case:

Delayed train journey

Train Canceled

On the other hand, if the train is canceled,

  • The travel by train sub-process is interrupted.
  • The passenger goes home.
  • The journey is aborted.

The process flow in for this scenario is highlighted in red:

Canceled train journey