Use cases help analysts determine how users will interact with a system by describing scenarios of system use through sequences of events initiated by an actor. A use case represents a collection of scenarios and can depict a system in terms of the goals users want to accomplish. Relationships like generalization allow use cases and actors to inherit behaviors, with child use cases adding to what is defined by the parent use case.

2. THE USE CASE
- The use case is a construct that helps analysts work
with users to determine system usage.
- A collection of use cases depicts a system in terms of
what users intend to do with it.
- Think of a use case as a collection of scenarios about
system use. Each scenario describes a sequence of
events. Each sequence is initiated by a
person, another system, a piece of hardware, or by
the passage of time.

3. -Including a Use Case
is also referred to as using a use case.
Extending a Use Case:-

4. In a use case model, a stick figure represents an
actor, an ellipse represents a use case, and an
association line represents communication between
the actor and the use case.
Generalization:-.
Classes can inherit from one another and so can use
cases. In use case inheritance, the child use case
inherits behavior and meaning from the parent, and
adds its own behavior. You can apply the child
wherever you apply the parent.

5. One use case can inherit the meaning and behavior
of another.
The generalization relationship can exist between
actors as well as use cases.

6. - Like classes and use cases actors can be in a
generalization relationship.
- The use case is a powerful tool for gathering
functional requirements.