Linking items
You link items on a Communication Diagram with message flows. Message flows depict an association between objects, acting as the mechanism by which information is exchanged between objects. Events and operations are carried by message flows. You cannot link actors to other actors.
To link items:
• On the Communication Diagram tab, click 
• Click the items to be linked
• You can also run from free space to an instance.
A message flow is displayed on the diagram to link the items.