Messages

Standard UML does not show any information about message calls on class diagrams. However, I've sometimes seen conventional diagrams like Figure 5.22.

These add arrows to the sides of associations. The arrows are labeled with the messages that one object sends to another. Because you don't need an association to a class to send a message to it, you may also need to add a dependency arrow to show messages between classes that aren't associated.

This message information spans multiple use cases, so they aren't numbered to show sequences, unlike communication diagrams.