The biggest difference between BPMN and traditional flowcharting is the support for events. An event is a signal that something happened, and BPMN lets you say how the process should respond.
Here Important definitions!
The Events can occur at the beginning ( Start Events) or at the end (End Events) or in the middle (Intermediate) of the process. Additionally, some events can happen on the Boundary of an activity. This indicates that the event can interrupt the activity, and will divert the sequence flow from the “normal” flow to another flow.
The following picture depicts a process of ordering some products which includes a Start event (a message event), of an Intermediate error event, a Boundary Timer event, and two End events.
The Events can be of catch (when a receive trigger is fired) or throw (which sends a trigger to the process) type.
The Start Events are always of catch type and the End Events are always of throw type. The Intermediate Events can be either of throw or catch type.There are various flavors of Events in BPMN 2.0. The Event Types are listed as follows:
|Message Events||Send or receive messages.|
|Timer Events||Are always of catch type and used to signify waiting for a specific time condition to evaluate to true.|
|Signal Events||Are used for publish and subscribe of signals.|
|Error Events||Are used for exception handling and they can occur only at the end of the process.|
|Termination Event||Are used to terminate the process and can occur only at the end of the process.|
|Conditional Event||Are used for rule-based triggers.|
|Escalation Event||Has been newly introduced in BPMN 2.0 to handle escalation conditions.|
|Compensation Event||Introduced to to handle compensation in the process.|
Depending on the combination of events, phase in which the event is triggered (Start, Intermediate, Boundary) and if the event interrupts an Activity, the event can be represented with a different combination of graphic notations.