A Transition may have multiple sources, meaning it is a join from several concurrent states, or it may have multiple targets, meaning it is a fork to several concurrent States.
You can show multiple transitions with either a vertical or horizontal orientation
in your state and activity diagrams. Both the state and activity diagram toolbar
provide separate horizontal and vertical fork/join buttons for each orientation.
The two orientations are semantically identical.
To create multiple transitions:
Identify the states involved. If necessary, place all of the states on the diagram first, and lay them out as desired.
Place either a horizontal or vertical fork/join on the diagram. Resize as needed.
If depicting multiple sources, draw transitions from each of the source states to the fork/join.
If depicting multiple targets, draw a transition from the source state to the fork/join; next, draw transitions from the fork/join to each of the target states.