A Message represents the content of a communication between two Participants. In BPMN 2.0, a Message is a graphical object (it was a supporting element in BPMN 1.2). An ItemDefinition is used to specify the Message structure.

In a Process that is not used in a Collaboration, the communication is not displayed, but a Message can be defined for Activities that send and receive Messages (such as a Send Task). Note that the display of Messages in a Process, Collaboration, or Choreography is optional.

A message belongs to a collaboration

: BpmnMessage (architecture_autodiagram)
Figure 45 : BpmnMessage (architecture_autodiagram)
OutputMessage : BpmnOperation [0..*]
ItemRef : BpmnItemDefinition [0..1]
EventDefinition : BpmnMessageEventDefinition [0..*]
Sender : BpmnSendTask [0..*]
InputMessage : BpmnOperation [0..*]
Receiver : BpmnReceiveTask [0..*]
MessageFlow : BpmnMessageFlow [0..*]
Collaboration : BpmnCollaboration [0..1]