Boundary Events

Last modified: November 7, 2024

Non-interrupting timer boundary events were in public beta in Studio Pro 10.15 and released in GA in Studio Pro 10.16.

Introduction

Based on Business Process Model and Notation (BPMN) 2.0, boundary events are a type of event that is attached to the boundary of an activity (such as a task or a sub-process) to handle exceptional situations or are triggered by certain behaviors.

There are two main types of boundary events:

Non-interrupting boundary events: These events do not interrupt the ongoing activity. When triggered, they allow the activity to continue while simultaneously starting a new path from the boundary event. As per BPMN 2.0 specification, non-interrupting boundary events are visualized as two dashed circles with an icon in the center.
Interrupting boundary events: When these events are triggered, they interrupt the normal path of the activity they are attached to. The activity stops and the process flow is redirected to the boundary event’s outgoing sequence path. As per BPMN 2.0 specification, interrupting boundary events are visualized as two solid circles.

Interrupting boundary events are not available yet in the current release.

Boundary Events are always displayed by 2 circles (either solid or dashed) and are linked by a dotted line to the parent activity. The icon inside the event indicates the type of event. For example, a clock indicates that it is a timer boundary event.

Below is an example of how a timer boundary event looks like:

Adding boundary events through drag and drop

Studio Pro now supports the following boundary event:

Timer

Getting started

You can add boundary events to the following activities:

When a boundary event is added to an activity, this activity is also referred to as the parent activity of the boundary event.

Adding Boundary Events

To add a boundary event to the above-listed activities, choose one of the following ways:

Select an event from the Events section in the workflow Toolbox and drag it onto one of the activities listed above.
Right-click one of the above-listed activities to open its context menu, and click Add boundary event.
Double-click one of the above-listed activities to open its properties dialog box, go to the Events tab, and in the > Boundary events section, click New to add a new boundary event.

To configure the properties of a boundary event, double-click the event to open its properties dialog box. For more information on how to configure the properties of a timer boundary event, see the Properties section in Timer.

Rearranging Boundary Events

You can rearrange boundary events in the following ways:

Right-click a boundary event to open its context menu and click Move boundary event left or Move boundary event right, or use the Ctrl/Command + Left arrow or Ctrl/Command + Right arrow shortcut keys.
Double-click the parent activity to open its properties dialog box and click Move up or Move down to change the order of the boundary events’ paths.

This does not change the order execution of the paths, as this is dependent on the expiration of the timer.

Execution

Boundary events are initiated when their parent activity is initiated. For example, for a timer with a fixed duration, it will start its count down when the parent activity is initiated. When the parent activity is completed before any of the boundary events are triggered, none of the activities in the boundary event path will be executed and all timers will be cancelled.

With non-interrupting boundary events, the parent activity remains active/in progress when a boundary event is triggered (which means that the parent activity is not interrupted). For example, when a timer boundary event on a user task is triggered after 2 days, this task will remain in progress and the path defined below the timer boundary event is executed. When the boundary event’s path reaches the End of boundary path, the workflow will await the completion of the parent activity.

Boundary Event Variables

Boundary event variables are available starting from Studio Pro version 10.16.

Boundary events have dedicated variables that can be used to get direct access to the values of the parent activity if it is either a user task or Call workflow activity. You can get information such as the parent activity’s DueDate, which can be used in the boundary event flow and its expressions. For instance, you can use the expression addDays($ParentTask/DueDate, -2) to configure a timer boundary event so that it is triggered two days before the due date of its parent user task.

The list of variables is described below:

$ParentTask – the parent user task of the attached boundary event
$CalledWorkflowInstance – the parent Call workflow activity of the attached boundary event

Current Limitation

The current release of boundary events has the following limitation which is actively being developed:

Non-interrupting timer boundary events currently have no recurrence. They are only executed once and will not repeat.