An event is a common BPMN process modeling element, which represents something that “happens” during the course of a process. Examples of process events are: “a telephone call”, “at three o’clock”, “a message has been sent”, “a message has been received”, “all tasks are completed”, “an error occurred.”
In a BPMN diagram, an event is graphically represented with a circle. A diversity of different types of events can appear in a business process, and BPMN is able to support the majority of them. In total, BPMN 2 supports more than 60 different types of events.
BPMN events can be distinguished according to several criteria: An event can initiate a process, occur when a process performs, or represent the end state of a process.
Start, intermediate and end events are distinguished with the thickness of the event’s border. A start event has a thin solid line, an intermediate event has a double thin line and an end event has a thick solid line.
Events can have different types of triggers, including: a message, a signal, time, an exception and a condition.
These types of event triggers are graphically distinguished by an icon within the event element.
An event can be triggered or it can be caught, which corresponds to send and received message.
In a BPMN diagram, a throwing and a catching event are graphically distinguished with a filled or unfilled trigger icon.
A catching event can also be positioned within a process control flow, or on the border of an activity.
When positioned within a process control flow, it represents a “waiting mechanism”.
On the other hand, when positioned on an activity border, it represents a “control flow redirection mechanism”.
The control flow redirection can also be defined as interrupting or non-interrupting. The first interrupts the corresponding activity, where the second doesn’t. Interrupting and non-interrupting boundary events are distinguished with solid or dotted border lines.