Boundary Events

Boundary events are attached to a task in workflow and “listen” for a trigger signal to perform an action.  

When the trigger signal is received, the workflow task is either interrupted and the sequence flow going out of the event is followed (interrupting behavior) or a new execution is created from the boundary event (non-interrupting behavior).

There are various boundary events used for different actions in workflow process:

·         Boundary error event

·         Boundary timer event

·         Boundary signal event

·         Boundary message event

Boundary error event

The Boundary error event is an interrupting event that catches error thrown inside the activity boundaries.

Once the error is caught, the Boundary error event handles it in the way we define it.

The best example for Boundary error event is bad online transaction. When the transaction is failed due to some reason, the user will be returned to homepage with the error message as “Transaction failed”.

The symbol is a circle with a lightning icon inside.

Boundary timer event

The Boundary timer event adds a timer on workflow process and when the timer is completed, the new sequence flow defined out of boundary will be followed.

The best example for Boundary timer event is password reset option. When the user did not reset the password within the given time, the reset link becomes invalid.

The symbol is a circle with a timer icon inside.

Boundary signal event

A boundary signal event listens to a signal being fired (from within the process instance or system-wide) while the activity upon which the event is defined is active.

The symbol is a circle with a triangle icon inside.

Boundary message event

When a boundary message event appears on the workflow process, it indicates that an incoming message can interrupt the sequence flow, and will divert the process from the “normal” flow to a defined “exception” flow.

The best example for Boundary message event is online order cancellation. When the user sends a cancellation message to the online seller, the order is cancelled from being shipped.

The symbol is a circle with an envelope icon inside.