The use case diagram show the functionality of the system from an outside-in viewpoint.

	Actors (stick men) are anything outside the system that interacts with the system.
	Use Cases (ovals) are the procedures by which the actors interact with the system
	Solid lines indicate which actors interact with the system as part of which procedures
	Dotted lines show dependencies between use cases, where one use case is 'included' in or 'extends' another.