Staring at a process diagram full of circles and diamonds? BPMN symbols explained simply: circles are events, rounded rectangles are activities, diamonds are gateways, and arrows show the order of work.
This guide is part of our wider look at business process management.
| Symbol | What it shows |
|---|---|
| Events | Drawn as circles containing symbols specific to the event type |
| Activities | Shown as rounded rectangles |
| Gateways | Shown as diamonds that lead to at least two possible outcomes |
| Sequence flows | Link activities in the order they are performed |
| Message flows | Communications between pools |
| Swimlanes | Containers that separate one set of activities from others |
These descriptions come from IBM’s BPMN overview. Notation details and tool support can change, so check the source before you rely on them.
How BPMN notation is organized
BPMN is a graphical language built on flowcharts. The Object Management Group has maintained it since 2005, and it exists to replace vague text descriptions with a diagram everyone reads the same way.
Every symbol falls into one of four families:
- Flow objects: events, activities and gateways, the things that define what happens.
- Connecting objects: lines with arrows that join flow objects.
- Swimlanes: containers showing who or which group does the work.
- Artifacts: extra information such as data objects, groups and annotations.
Once you can place a symbol into one of these families, most diagrams stop looking intimidating. You read the flow objects first, follow the arrows, then check the lanes to see who owns each step.
Events: the circles
An event is a trigger that starts, alters or concludes a process. BPMN depicts events as circles, and a small icon inside the circle tells you the type.
The position of the circle matters as much as its icon. Start events initiate a process, intermediate events occur during a process, and end events conclude it.
By convention the border tells you which is which:
- A thin single line usually marks a start event.
- A double line usually marks an intermediate event.
- A thick line usually marks an end event.
Events can include messages, timers and dates, transactions, errors, escalations and requests. A start event with an envelope icon, for example, means the process begins when a message arrives. An empty circle simply says the process starts or ends without a specific trigger.
Activities: the rounded rectangles
An activity is an action or task performed during the business process. Business process diagrams show activities as rounded rectangles, with a short verb-and-noun label such as “Approve invoice”.
Activities can be simple or more complex, including subprocesses and multiple iterations. A subprocess hides a whole group of steps inside one box, which keeps a high-level diagram readable.
A good habit is to label every activity with an action. If a box reads “Invoice” you cannot tell what happens to it, but “Check invoice” is clear to anyone on the team.
Gateways: the diamonds that route work
A gateway controls where the flow goes next. Shown as diamonds, gateways lead to at least two possible outcomes depending on the decision made.
The marker inside the diamond tells you the rule:
- Exclusive: depicted as a diamond containing an X; the workflow must proceed down only one of the available options.
- Inclusive: depicted as a diamond containing a circle; the options are not mutually exclusive, so more than one path may run.
- Parallel: a diamond containing a plus sign; the workflow splits into multiple simultaneous paths.
- Complex: a diamond containing an asterisk, for routing rules the other types cannot express.
The most common mistake is mixing these up. An exclusive split means “either, or”, while a parallel split means “all of these at once”, and the two lead to very different behavior when the process runs.
Flows, pools and lanes
Arrows and containers turn separate shapes into a readable story. Sequence flows link activities in the order that they are performed within the business process, and they are drawn as solid lines with arrowheads.
Message flows are different. They are communications that flow between pools, which are discrete departments or other groups, and they are drawn as dashed lines.
Swimlanes are containers that separate one set of activities from others. A pool usually stands for a whole participant such as a customer or a supplier, and lanes inside it split the work among roles or teams.
Because lanes show who does what, they are especially useful when you want to see handoffs. Every time an arrow crosses from one lane to another, someone is passing work on, and that is often where delays hide.
Artifacts and reading a real diagram
Artifacts provide supplemental information about the process, such as data objects, groups and annotations. They never change the flow itself, so you can read the diagram without them and add them for clarity.
To read an unfamiliar diagram, work through it in this order:
- Find the start event and the end events.
- Follow the sequence flows through each activity.
- Stop at every gateway and note what condition decides the path.
- Check the lanes to see who owns each step.
- Look for message flows that cross into another pool.
When you are ready to draw your own, the next step is learning how to model a full process end to end; our guide to BPMN process modeling covers that. Once a process is running, you can compare the diagram against real event logs with process mining.
A short worked example
Picture an expense claim. A start event fires when an employee submits a form, and an activity called “Review claim” follows in the finance lane.
Next comes an exclusive gateway asking whether the claim is valid. One path leads to “Pay claim” and then an end event, while the other returns the claim to the employee with a request for changes.
Even this tiny diagram uses events, activities, a gateway, sequence flows and lanes together. Reading it aloud, step by step, is a quick way to test whether the diagram says what you mean.
Common mistakes with BPMN symbols
- Using a task box where a gateway is needed, hiding a decision inside a label.
- Leaving gateways unmarked, so readers guess whether paths are exclusive or parallel.
- Drawing sequence flows between pools instead of message flows.
- Overloading one diagram with every artifact until the main flow disappears.
- Skipping end events, which leaves the outcome of each path unclear.
Keeping a diagram small and consistent usually matters more than using every symbol available. Most business processes can be described well with events, activities, gateways, flows and lanes alone.
Frequently asked questions
What do the circles in BPMN mean?
Circles are events. They mark where a process starts, something that happens during it, or where it ends, with an icon inside showing the type.
What is the difference between a sequence flow and a message flow?
A sequence flow links activities in the order they are performed. A message flow carries communication between pools, such as between departments.
What does a diamond mean in BPMN?
A diamond is a gateway. It splits or merges the flow, and the marker inside, such as an X or a plus sign, tells you whether paths are exclusive or parallel.
Who maintains the BPMN standard?
The Object Management Group has maintained BPMN since 2005, according to IBM’s overview.
