Episode 2 · March 26, 2026 · Hosted by Sebastian
Is Your Diagram Actually Correct? Structural Validation & Token Simulation
Four hidden BPMN traps you only catch when you run the process, not when you look at it: the silent multi-merge, fake decisions from the wrong gateway type, implicit parallelism, and non-terminating live loops. Plus why interrupting and non-interrupting events behave so differently, and why token simulation is the real quality gate.
Your diagram looks correct. But is it actually correct?
The big takeaway
A diagram can look perfect and still be logically broken.
If you don't simulate it, you're not validating behaviour, you're just reviewing shapes.
What we walked through
- 01
The silent multi-merge
A parallel split without a proper join duplicates your entire flow. It looks fine in review, but suddenly you're sending two interview invites, two rejections, two of everything. Token simulation exposes it instantly: if you see two tokens, something's off.
- 02
Fake decisions from the wrong gateway type
Using an exclusive gateway where you're actually waiting for external events, like a candidate reply or time passing, implies control where there is none. Switch to an event-based gateway: from "we decide" to "we react".
- 03
Implicit parallelism
Two outgoing flows from a task are a hidden parallel gateway. BPMN allows it, but humans miss it, and the result is unintended loops, duplicate paths or even endless executions. Rule of thumb: never split without an explicit gateway.
- 04
Non-terminating live loops
Small modelling oversights can create flows that never end. You won't catch this in a quick visual review, but the token simulator will either loop forever or behave unexpectedly.
- 05
Cancellation semantics are subtle but critical
A dashed or solid event border completely changes behaviour. Non-interrupting (dashed) runs in parallel and the main flow continues. Interrupting (solid) stops the process. We also discussed when to use process-wide cancellation, boundary events or scoped subprocesses.
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