The basiscs – the activity
To start: BPMN defines a set of “icons”, which are used to represent different parts of a process.
The first icon, one will likely come across, is the “activity”. It stands for an activity that is part of the documented process.
There are different types of activities, which can take place in a process; the one we’re seeing here is a simple “Task”. A task is an atomic activity within a process; it’s commonly used when the process activity cannot be broken down into any more detailed actions.
Different kinds of a BPMN event
Start and End event
One sole task by itself would in principle already be a “valid” BPMN process. In practice, several activities are commonly strung together in a sequence. The start and end of an event is placed at the front and end respectively. Both are represented by an “event”, which is commonly marked by a circle.
- Start event: the start event is a single thin-lined circle.
- End event: the end event is a bold-lined circle.
Intermediate events and triggers
Apart from a start and end event, there are also intermediate events which can be triggered over the course of a process.Such events are represented by double-lined circles. They generally come with a variation of symbols embedded in their center to define which kind of event we are looking at. Typical events can be:
- Messages (1:1) being sent or received
- Signals (1:n) being sent or received
- Conditions or (context) states changing
If the pictogram in the circle is filled (typically black), it means the process is triggering an event.
If the pictogram is outlined (typically black outline with white filling), it means the process is catching an event. One important to note here is, that the process generally pauses/halts until the event actually is being caught by the process. If no event is ever triggered, the process will basically halt and never end.
Lets look at the following simple example:
- Our start event is triggered by the condition “hunger”
- We then choose our desired toppings
- Then the process halts until we receive an invitation to place our order
- Next we mark the desired toppings on the order form
- Last, we hand over the order form – thereby “messaging” the information to the pizza shop
A simple analogy which is very often used to describe the workings of BPMN is the use of a token like in a board game. Every process is being “instantiated” by putting a token on the first event or activity in the process. The token then progresses towards the end of the process – step by step. When there’s a catching event, the token waits on the activity or event before it until the event actually is triggered.
When the token finally reaches the end event, the token is “consumed” and the process is terminated.
Continue to next chapter
Continue on to the next chapter on how a process can end.