The pit crew has 7 seconds. Tires need changing, fuel needs topping up, and the engine needs checking — all at the same time. How do you model work that happens in parallel?
Before we hit the racetrack, you need to understand one concept that makes BPMN click: the token.
Imagine a marble rolling through your process diagram. It starts at the start event, passes through tasks one by one, and eventually reaches the end event. When a task is being worked on, the marble sits there and waits. When the task is done, the marble rolls forward to the next element.
At an exclusive gateway (which you learned in the Shoe Shop), the marble takes one path. Simple. But what happens when work needs to happen at the same time?
Token concept: Imagine a marble rolling through your diagram. At a parallel gateway, the marble is cloned. At an exclusive gateway, the marble picks one path. At a closing gateway, the marbles merge back into one.
Gonzalez is a Formula One driver. Successful, famously impatient, and leading the field in the final race of the season. Ten laps in, he needs a pit stop. His team has to change the tires and refuel the car - and they need to do it simultaneously. Every second in the pit costs positions on the track.
If the fuel team had to wait for the wheel team to finish, or vice versa, the pit stop would take twice as long. Gonzalez would lose the championship. The process needs to express: "these things happen at the same time."
That's what the parallel gateway does. It looks like a diamond with a plus sign inside - and unlike the exclusive gateway, it has no question on top. No decision is being made. It simply says: "all paths activate simultaneously."
Back to the token concept: when the marble hits a parallel gateway, it gets cloned. If there are two outgoing paths, you now have two marbles. Three paths, three marbles. Each one rolls independently through its branch.
At the other end, a closing parallel gateway waits. It knows how many marbles to expect. It won't release a single marble until all of them have arrived. That's the synchronization point - the moment where parallel work comes back together.
Parallel gateways are diamonds with a plus sign. They activate all outgoing paths at once - the token is cloned. The closing gateway waits for every clone to arrive before releasing a single token forward.
Here's how Gonzalez's pit stop works in BPMN:
The process starts when Gonzalez pulls into the pit lane. The token hits the parallel gateway and splits into two:
Both teams work at the same time. The wheel team is fast - four tasks done in seconds. The fuel team is slightly slower - refueling takes longer. Gonzalez is getting nervous.
But the closing gateway waits patiently. It doesn't release Gonzalez until both tokens arrive. The fuel team closes the gas cap, the second token reaches the gateway, and Gonzalez rockets back onto the track.
The parallel gateway isn't just for racing. It shows up everywhere:
Whenever you hear "at the same time," "simultaneously," or "in parallel" - that's a parallel gateway.
The exclusive gateway (X) and parallel gateway (+) look similar. Even experienced modelers mix them up. Build a mental bridge now:
One makes a choice. The other doesn't choose - it does everything.
Exclusive (X): Cross out all paths except one. Parallel (+): Add all paths together. Build this mental bridge now - it will save you from the traps in Chapter 4.
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