This document defines and explains the key elements of a use case diagram including actors, use cases, the system boundary, and communication lines. It provides examples of primary and secondary actors, describes use cases as sequences of actions performed by the system, and explains different types of relationships between use cases such as include and extend dependencies. Finally, it includes an example use case diagram for a railway reservation system to demonstrate these concepts.

1. UML
Diagrams :
Use Case Diagram

2. INTRODUCTION :
 Use Case Diagram is invented by Jacobson.
 Specifies the static use case view and functionality of a
system.
 Useful in modeling the behavior of system.
 Used to gather requirements and to get outside view of a
system.
 Identifies external and internal factors influencing a
system.
 Shows interaction among actors.

3. Terms and concepts :
1. Actor :
 performs functions of a system
 Represents role played by a person that interacts
with a system.
 Responsible for giving input to system .
 Uses processed output for performing particular
action.

4. i. Primary Actor :
 People who performs main system functions.
ii. Secondary Actor :
 People who performs admin/ maintenance task.
iii. External Hardware :
 Hardware devices which are part of application.
iv. Other Systems :
 Other systems with which the system must interact.

5. 2.Use Cases :
Indicates set of functions performed by user.
Describes sequence of actions that the system performs .
Must have unique name(either simple or qualified).
Represented by “Ellipse” .
Symbol -
Place order

6. 3.System Boundary :
 Shows how the user interacts with the system.
 Class in which use cases are executed.
 Represented by use cases within a rectangle and actors
will outside of system boundary.
 Symbol -
System
Boundary

7. 4. Communication Line :
 Used between various components.
 It can be association, generalization or dependency.
i. Association :
 Relationship between use case and actor.
 Represented by solid line(either unidirectional or bi-
directional).
 Symbol -

8. ii. Generalization :
 Relationship between actors or in between use cases.
 Represented by solid line with hollow arrow.
 Symbol -
iii. Dependency :
 Relationship between uses cases.
 Represented by dashed line with arrow.
 Symbol -

9. i. Include Dependency :
 Relationship in which use case consist features of
another use case.
 Shows interaction between base use case and include
use case.
 Represented by “<<include>>” stereotype.
 Symbol -
View balance Modified account
<<include>>

10. ii. Extend Dependency :
 It consist of extension of behavior from one use case to
another.
 Shows interaction between base use case and extension
use case.
 Represented by “<<extend>>” stereotype.
 Symbol -
Withdraw money Enter amount
<<extend>>

11.  Example - Use case diagram of Railway Reservation
system :-
Student Librarian
Pay money
Request for form
Fill form
Collect ticket
Wait for token
Give form