To organize Activities in a process model, BPMN offers the use of Swimlanes. Swimlanes represent Roles, Responsibilities and organizational structures.

There are two constructs:

• Pools - used to border process participants, usually representing one organization.
• Lanes - divide Pools to clarify structures within one organization (i.e. different sections).

A Process belongs to one Pool, an Activity belongs to one Lane.

Pools

Like in the Swimlane analogy, a 'Pool' consists of 'Lanes'.

Pools model abstract roles like 'Buyer' or 'Seller' or 'Distributor' as well as concrete instances of these roles (e.g. 'Amazon.com' and 'FedEx'). The level of detail depens on the model's intention and most notably about its granularity. Modeling for the Management it might be reasonable to represent external participants as abstract roles and to focus on the process in the own company's view.

Communication between Pools that means over organizational borders is modelled with Message Flow. Message Flows represent information that are exchanged between Pools. Message Flow can be attached to concrete Activities, to Message Events and even to just the Pool only

It is possible to abstract from concrete processes in Pools. If a model is focused on communication between organizational structures, it might be appropriate to collapse Pools and to just explicitly model Message Flow. Maybe details about another Pool's process are not even known. BPMN uses Collapsed Pools to hide a Pool's process internals.

Lanes

Lanes divide Pools to group Activities and to define Responsibilities within one organization. Lanes may be uesd to group over functional as well as over regional criteria. Lanes follow the concept of organizational structures.

It is also possible to interlace Lanes. Hierarchical Lanes are called Nested Lanes.