So far, our processes had a very isolated focus. They didn't consider or react on any external input (e.g. a message from a customer), except the start of the process. The entire chapter is about, using events as part of the process flow to act and react with the business environment.
Events mark a state in a process, at least at the start and at the end. The BPMN 2.0 notation counts more than 60 different events, which emphasizes their importance for business process modeling.
Events are required to show, at which place the business process has to wait for external input to react accordingly. Those events could be:
- A response from a customer
- A reached point in time
- A certain condition (e.g. budget approved)
Three Aspects when using Events
Before we dive deeper into the world of events, it's important to know there are three aspects behind the usage of events. These aspects are helpful in understanding the event behavior and using them correctly.
- There are start events, intermediate events and end events - WHERE is an event used?
- Events can be catching or throwing - HOW is an event used?
- Events can be specific by a type - WHICH event is used?
Start, Intermediate, and End Events
Based on their occurrence in the process, events are categorized as start events, intermediate events and end events. You already know start and end events - let's review them and take a closer look at intermediate events.
Plain Start Event
These events can only occur at the start of a process, as they're representing the trigger. Hence, they can only have one outgoing sequence flow.
Plain Intermediate Event
Intermediate events need to have an incoming and outgoing sequence flow. They mark a state in a process without impacting the process flow. The token just "passes through" and marks the state.
Why is this useful? Blank intermediate events can be used to highlight a certain progress (Milestone) in the process flow, for example:
- Mark a stage as "phase 2 completed"
- Mark manufacturing status "component X manufactured"
Plain End Event
This event marks the end of the process, as it's representing the process goal. Hence, it can only have an incoming sequence flow.
Intermediate Events as Milestones
In some processes it might be useful to mark the state when a certain milestone has been reached. If the process gets executed in a technical environment, the time between different milestones could be measured more specifically. However, such milestones are always optional. Their importance depends on what they are actually describing in the process.
Key Takeaways - BPMN Events
Select each level in the figure for more information.