Lesson 1 of 3
Pools: separate participants
A Pool represents a separate participant in a process — a distinct organisation, an independent system, or a major actor whose internal process may or may not be relevant to the diagram.
Entities that operate independently and communicate by passing messages each get their own Pool. A Customer, a Supplier, a Retailer, and an External Payment Gateway are each a Pool.
Lanes: subdivisions within a Pool
A Lane is a horizontal or vertical subdivision inside a Pool. It represents a role, department, or system within the same organisation. Finance Clerk, Finance Manager, and Payment System are all part of the same company — so they are Lanes inside a single Pool, not separate Pools.
The rule beginners always get wrong
Sequence Flow (solid arrow) goes between elements inside the same Pool. Message Flow (dashed arrow) goes between Pools. This is not a style preference — it is a rule in the BPMN 2.0 standard. Breaking it makes the diagram ambiguous about organisational boundaries and technically incorrect.
The practical distinction
Ask: Are these two actors part of the same organisation? If yes → Lanes inside one Pool. If no → separate Pools connected by Message Flow.
| Situation | Correct structure | Connection type |
|---|---|---|
| Finance Clerk and Finance Manager in the same company | Two Lanes inside one Company Pool | Sequence Flow (solid) |
| Company and its Supplier | Two separate Pools | Message Flow (dashed) |
| HR department and IT department in the same company | Two Lanes inside one Company Pool | Sequence Flow (solid) |
| Company and external Payment Gateway | Two separate Pools (Gateway is collapsed) | Message Flow (dashed) |
| Customer placing an order and the retailer fulfilling it | Two separate Pools | Message Flow (dashed) |
Multiple Lanes: best practices
- Use Lanes when different roles inside the same organisation perform different steps. This makes handoffs visible — every Sequence Flow crossing a Lane boundary is a handoff.
- A single-Lane Pool is fine if all the work happens within one role or department.
- Lanes represent roles, not individuals. 'Finance Clerk' not 'Sarah Thompson.'
- Systems can be Lanes too. If an automated system performs a step, give it a Lane: 'Payment System', 'CRM', 'ERP.'
Wrong: A Sequence Flow connects 'Send Invoice' in the Supplier pool to 'Receive Invoice' in the Company pool.
Corrected: A Message Flow (dashed) connects the Supplier Pool to the Company Pool. Inside the Company Pool, 'Receive Invoice' is the first task in the Finance Clerk Lane.
✓ When to use
- Pools for any actor that is a separate organisation, external party, or system operating independently
- Lanes to subdivide a Pool by role, department, or internal system
- Lanes even for a single handoff — two tasks in different lanes make one handoff visible
✗ When not to use
- ✕Don't use Pools for internal departments — they should be Lanes
- ✕Don't create a Lane for every individual person — Lanes are roles, not named individuals
- ✕Don't overload a Pool with more than 5 Lanes — it usually signals the process needs decomposition