Event, in BPMN, graphically represents the matters and phenomenon that occur in business processes by using a circle shape. It is also an important modeling element that affects the subsequent business process execution.
Overview of Event
In general, event is a word meaning that something happens, and its concrete definition is very broad and is not enumerable. Furthermore, even if we narrow down its definition range to "something happens in business process execution," we can see, by considering what could actually happen, that there are countless possibilities. Thus, BPMN categorizes those innumerable "something" into a couple of categories and limits the definition to what can impact the order or timing of activities in business processes. For example, "start of a task," "completion of a task," and "message passing under a certain condition" are included. These events can play roles of either Catching Events or Throwing Events.
Event in BPMN is an important flow object (a modeling element that connects to Sequence Flow), just like Activity and Gateway, and indicates the point of occurrence of "something" that could affect the order or timing of activities. Event is classified into 3 types shown below based on the timing of occurrence.
A specific action is triggered when conditions and situations tied to the movement of business process are received at certain timing in the pre-determined way. In other words, Event can be considered as a "trigger" that initiates an action to be done next upon pre-defined conditions and situations (catch). Start events and many intermediate events play this role, and they are further categorized into a couple of types of events based on various "triggers."
- E.g. Process that utilizes documents delivered from other departments (other business processes) to do its own task
- We can consider that this process is triggered to start at the point of receiving "(delivered) documents."
In response to conditions and situations that trigger actions, as the "results" of them, actions are performed as defined in advance. In other words, Events play a role to define actions to be taken after receiving triggers (throw). End events and some intermediate events play this role, and they are classified into a couple of types of events based on various "results."
- E.g. "Approval Process" and "(Approved Task) Execution Process"
- This is a case in which the completion of one business process is announced as a kind of "signal" to start other business processes, and we can consider that the result, in which the subsequent business process is started, is defined at the end of the preceding business process.
Categorization of Events and Notation for Markers
When business processes are described, BPMN categorizes Events based on the characteristics into various types and defines a special marker (symbol) for each of them. Upon the transition from BPMN1.0 to BPMN1.1, some markers are added and modified for the sake of visual understandability and easy notation. Types of "Events" are shown below.
Categorization based on the Point of Occurrence of Event
As shown above, in common, all events are denoted with "small circles." They are differentiated by the thickness and the number of lines.
Classification Based on Triggers and Results of Event
- BPMN1.1 Specification (2008-01-17)