Boundary events help us describe how to handle errors, escalations, and time-outs that require deviations from the happy path.

An escalation boundary event

  • Every boundary event is associated with a particular activity.
  • Boundary events are intermediate, catching events.

The most common types of boundary events are error, escalation, message, and timer events.

Common boundary events

Internal exceptions are caused by something that happens within the activity with which the boundary event is associated. Internal exceptions trigger error and escalation boundary events.

  • The purpose of an error boundary event is to handle errors or exceptions that occur during the execution of an activity within a process.
  • The purpose of an escalation boundary event is to escalate a situation to a higher level of authority or management for resolution when a specified condition or threshold is met.

External exceptions trigger message and timer boundary events.

  • message boundary event is triggered by receiving a message from an external source, such as another participant, process, or system.
  • timer boundary event triggers a process flow after a certain amount of time has elapsed. It’s commonly used to manage deadlines or trigger the sending of reminders and notifications.

Boundary events can be interrupting or non-interrupting.

  • When activated, interrupting boundary events will—as their name suggests—interrupt the activity with which it is associated and initiate an alternative process flow.
  • When triggered, a non-interrupting boundary event will initiate a process flow without inhibiting the execution of the activity with which the boundary event is associated. In other words, a non-interrupting boundary event will trigger an additional process flow.