Associations are handled the same way as linking elements in other diagrams. Drag the cursor from Flight to FlightDescription and release. The Diagram pane will show the new association as a blue line. If you look in the Editor after creating the association, you'll see that Flight has member named lnkFlightDescription . Note that lnkFlightDescription does not appear in the Flight node of the Diagram pane.
Most links go from one class to another.
But some can be self-links, starting and ending at the same class. You can put a self-link in our model to distinguish between a flight plan and an actual flight. Make the diagram link display to be Direct. Then draw a self-link on Flight . Below is a snapshot of the diagram so far.