State about the Use Case Diagram

A use case diagram represents a set of use cases, actors and their relationships. These diagrams shall be used to model context or requirement of a system. It consists of use cases, actors, generalization, dependency, relationship, association, constraints, roles, packages and instances. The use case diagram makes systems, subsystems, and classes accessible by presenting an outside view of how elements may be used in context. The notation for use cases and relationship between use cases, base cases and extend cases is shown as:

 Figure: Relationship among use cases