However, you cannot connect two Use Cases by more than one Extends line, and you cannot connect two Use Cases by an Extends line if they are already connected by an Includes or Communicates line. An Extends line cannot be drawn from a Use Case to itself. You might use six different Sequence diagrams to model this logic, each one showing a definitive course of action. Alternatively, we can wrap up all of this logic into one neat State diagram. Each state reflects the state of the drawing cursor.
Actions cause transitions between the states.