UML Diagrams :

Use Case Diagram

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.

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.

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.

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

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

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 -

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 -

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>>

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>>

Example - Use case diagram of Railway Reservation system :-

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