There can be 5 relationship types in a Use Case diagram.
•	Association between actor and Use Case. eg open account   deposit funds
•	Generalization of an actor. one actor can inherit the role of other actor in activity#1 for activity#2  open account   deposit funds then transfer to credit card
•	Generalization of a Use Case. The child use case (or actor) is an enhancement of the parent use case (or actor). eg use case called “Pay Bills”. a generalization of “Pay by Credit Card”, “Pay by Bank Balance” etc.
•	Extend between two Use Cases.  extends the base use case and adds more functionality to the system
•	Include between two Use Cases. including (base) use case is incomplete without the included use case.