# BPMN pools and lanes

A pool is a participant, usually a whole organisation or system. A lane subdivides a pool into roles. Between pools you can only send messages, which is exactly right: you cannot control another company's process.

That constraint is the single most useful thing about BPMN.

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## When it matters

* Cross-organisation processes.
* Any process where the handoffs are the interesting part.

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## The symbols

| **Symbol**     | **Means**                                                             |
| -------------- | --------------------------------------------------------------------- |
| Pool           | A participant. Contains a whole process, or is drawn as a black box.  |
| Black box pool | Collapsed, with no internal detail. The usual way to show a customer. |
| Lane           | A role or system inside a pool.                                       |
| Message flow   | The only connection allowed between two pools.                        |

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## A few things that catch people out

* Draw external participants as black box pools. You do not know their internal process, and pretending you do is misleading.
* One process per pool. Two processes in one pool is a modelling error.
* Lanes are organisational, not technical. They do not change execution.

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## Related

[BPMN data objects and storesWhat the process reads and writes.](https://help.gocapable.com/diagrams/bpmn-data-objects-and-stores.html)

[BPMN groups and annotationsNotes that carry no semantics.](https://help.gocapable.com/diagrams/bpmn-groups-and-annotations.html)

[BPMN notation referenceBack to the full symbol reference.](https://help.gocapable.com/diagrams/bpmn-notation-reference.html)

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_Sequence flow stays inside the pool._