Pool
The rectangular container representing a participant — an organization, system or role. A Pool contains one process (or is a black box) and talks to other Pools only through Message Flows.
The Pool answers *who participates*: a company, a department, a customer, an external system. Everything inside belongs to that participant; communication between Pools happens exclusively through dashed Message Flows — sequence flows can never cross a Pool border.
Internally, a Pool may be divided into Lanes to separate roles within the same participant.
When to use and avoid
When to use
To model collaborations between different participants (Customer × Store).
When message exchanges between organizations/systems must be shown.
To delimit each party's responsibility precisely.
When NOT to use
To separate roles inside the same participant — that's what Lanes do.
In single-participant models with no external interaction — the Pool frame is optional noise.
Expecting sequence flows to cross Pools — invalid; use message flows.
Business example
Customer and Store collaborating
Open this example in the HEFLO process editor and explore the diagram from the inside.
Open in the HEFLO editor →Step by step
- The Customer Pool is a black box — we only see its messages.
- The Store Pool (highlighted) receives the order via a message start, processes it, and confirms by message.
- The dashed connectors are Message Flows — the only legal channel between Pools; note no sequence flow crosses the border.
Differences
Pool vs Lane
Pool = autonomous participant (message flows between Pools). Lane = internal subdivision of a Pool (sequence flows cross lanes freely). Who participates → Pool; who does what inside → Lane.
White-box vs black-box Pool
A white-box Pool exposes its internal process. A black-box Pool is drawn empty: only its message exchanges are visible. Use black boxes for partners whose internals are unknown or irrelevant.
FAQ
Can a sequence flow connect two Pools?
Never — sequence flows live inside one Pool. Between Pools, only Message Flows.
How many processes fit in one Pool?
Exactly one (or none, for black boxes). Multiple participants means multiple Pools.