ANSWER

A “swimlane” is a generic industry term used to describe the grouping of common activities in a process diagram into labeled rectangular area.

Two of the more common standards for process diagrams are the UML Activity Diagram and the BPMN Business Process Diagram (aka Swimlane Diagram).

In UML, the generic “swimlane” is represented by a concept that is called an Activity Partition.  The UML 2.0 specification describes an activity partition as a “kind of activity group for identifying actions that have some characteristic in common.”  Activity Partitions can be further divided into Activity Sub-partitions. There is really no difference between an Activity Partition and an Activity Sub-Partition other than the level at which the group activities based on a common set of characteristics.

In BPMN, the generic term “swimlane” is represented by either a Pool or a Lane in the swimlane diagram.  A Pool is a graphical representation of a participant within the business process diagram.  Pools can represent different businesses, a generic business partner (like a supplier, manufacturer, or buyer), or be more granular if modeling a single business without external dependencies.  Additionally, a Pool may reference a process and show the internal details (white box), or it may have no internal details (black box). A Pool acts as a container for the activities and sequence flows between activities. 

Lanes are mentioned in the BPMN specification as being used to organize and categorize activities within a pool.  However, the precise meaning of a lane or its appropriate scope is left up to the modeler, as the specification is silent in this area.

So, besides the fact that a Lane is used to subdivide a Pool, what is ultimately the difference between the two?  Sequence flows can cross Lanes between activities but they cannot cross Pools. Only messages can pass between Pools.  This is by design and is a major benefit of the BPMN notation. Messages indicate transfer of information within a conversation between two parties.  These are points of risk within the business process and deserve extra attention.  Both minimizing points of communication as well as ensuring clear communications take place help reduce process risk.

Additionally, participants of one pull have no control over the completion of activities that may occur in another pool. Whereas, activities divided between lanes can sometimes be performed by the same person, even if they that person is performing a different role (wearing multiple hats).