On Communication Diagrams, the Messages are decorated by a small arrow in the direction of the Message close to the Message name and sequence number along the line between the lifelines ... Source OMG Systems Modeling Language (SysML) 1.6
A found Message is denoted with a small black circle at the starting end of the Message. Source OMG Systems Modeling Language (SysML) 1.6
A lost Message is denoted with a small black circle at the arrow end of the Message. Source OMG Systems Modeling Language (SysML) 1.6
An object deletion Message (messageSort equals deleteMessage) must end in a DestructionOccurrenceSpecification. Source OMG Systems Modeling Language (SysML) 1.6
An object creation Message (messageSort equals createMessage) has a dashed line with an open arrow head. Source OMG Systems Modeling Language (SysML) 1.6
A reply Message (messageSort equals reply) has a dashed line with either an open or filled arrow head. Source OMG Systems Modeling Language (SysML) 1.6
A synchronous Message (messageSort equals synchCall) has a filled arrow head. Source OMG Systems Modeling Language (SysML) 1.6
An asynchronous Message (messageSort equals asynchCall or asynchSignal) has an open arrow head. Source OMG Systems Modeling Language (SysML) 1.6
The form of the line or arrowhead reflects properties of the message Source OMG Systems Modeling Language (SysML) 1.6
The send and receive events may both be on the same lifeline. Source OMG Systems Modeling Language (SysML) 1.6
17.4.4.1 Message - A message is shown as a line from the sender MessageEnd to the receiver MessageEnd. The line must be such that every line fragment is either horizontal or downwards when traversed from send event to receive event. Source OMG Systems Modeling Language (SysML) 1.6
