Conversation
See: Business Process Modeling Notation (BPMN), version 2.0, page 124 and the following.
The BPMN conversation diagram has been introduced with BPMN 2.0 to provide a big picture of the interactions (in terms of related message exchanges) between collaborating participants.
The BPMN conversation diagram is similar to the BPMN collaboration diagram, but its pools are not allowed to contain a process and a choreography is not allowed between the pools.
The BPMN conversation diagram differentiates three basic elements.
Conversation nodes (Communication, Sub-conversation)
Participants (Pools)
Conversation links (message flow, participates in)
They are described in the next chapters.