Sending message between State Diagrams

• Dashed arrowed line between objects enclosing substates. The Event signatures of the transitions in the two objects must match
• Dashed line from transitions between states of an object to the box enclosing its sub-states with corresponding event signatures.
• Sub-states may be or-substates (disjoint) or and-substates (concurrent)
• History indicator will allow resumption of activities held in its memory.