Use Case Diagram

Object Oriented Design and Analysis
Use Case Diagram

Introduction
Use-cases are descriptions of the functionality of a system
from a user perspective.

Depict the behaviour of the system, as it appears to an outside
user.

Describe the functionality and users (actors) of the system.

Show the relationships between the actors that use the
system, the use cases (functionality) they use, and the
relationship between different use cases.

Document the scope of the system.

Illustrate the developer’s understanding of the user’s
requirements.

Use Case Diagram, purpose
• Use case models are developed at different levels of abstraction
– system, system component, or a class.
• Use case modelling is an iterative and incremental process.
– If user requirements change, the changes should be made in all the
affected documents.
Requirements
document
(text in natural language)
Class
diagrams
Activity
diagrams
Sequence
diagrams
Statechart
diagrams

Use Case diagrams, basic UML notation
 Use Case: A Use Case is a description of a set of
interactions between a user and the system.
 Components of use case diagram:
 Actor
 Use case
 System boundary
 Relationship
use case name
use case name
use case name

Use cases: Information captured
• Actors
• Relationships with other use cases
• Pre-conditions
• Details
• Post-conditions
• Exceptions
• Constraints
• Alternatives

ACTOR
 An actor is some one or something that must
interact with the system under development
 Actors can be human or automated systems.
 Actors are not part of the system.
 UML notation for actor is stickman, shown below.
Student Faculty Employee

ACTOR (contd..)
• It is role a user plays with respect to system.
• Actors carry out use cases and a single actor
may perform more than one use cases.
• Actors are determined by observing the direct
uses of the system

Primary and Secondary Actors
• Primary Actor
– Acts on the system
– Initiates an interaction with the system
– Uses the system to fulfill his/her goal
– Events Something we don’t have control over
• Secondary Actor
– Is acted on/invoked/used by the system
– Helps the system to fulfills its goal
– Something the system uses to get its job done

USE CASE
What is USE case?
 A use case is a pattern of behavior, the system
exhibits
 The use cases are sequence of actions that the
user takes on a system to get particular target
 USE CASE is dialogue between an actor and the
system.
• Examples: Add a course

Contd..
• A use case typically represents a major piece of
functionality that is complete from beginning to end.
• Most of the use cases are generated in initial phase,
but may add some more after proceeding.
• A use case may be small or large. It captures a broad
view of a primary functionality of the system in a
manner that can be easily grasped by non technical
user.

System Boundary
 It is shown as a rectangle.
 It helps to identify what is external versus internal, and
what the responsibilities of the system are.
 The external environment is represented only by actors.

Relationship
• Relationship is an association between use case and actor.
• There are several Use Case relationships:
 Association
 Extend
 Generalization
 Uses
 Include

Extend Relationship
 The extended relationship is used to indicate that use
case completely consists of the behavior of another use
case at one or specific point
 use cases that extend the behavior of other core use
cases. Enable to factor variants
 The base use case implicitly incorporates the behavior of
another use case at certain points called extension
points
 It is shown as a dotted line with an arrow point and
labeled <<extend>>
Login
Register
New User
<< extend>>

Generalization
 Generalization is a relationship between a
general use case and a more specific use case
that inherits and extends features to it
 use cases that are specialized versions of other
use cases
 It is shown as a solid line with a hollow arrow
point

Uses Relationship
 When a use case uses another process, the
relationship can be shown with the uses
relationship
 This is shown as a solid line with a hollow arrow
point and the <<uses>> keyword

Include Relationship
 Include relationships insert additional behavior into a
base use case
 use cases that are included as parts of other use cases.
Enable to factor common behavior.
 The base use case explicitly incorporates the behavior of
another use case at a location specified in the base.
 They are shown as a dotted line with an open arrow and
the key word <<include>>

Extend vs Include

18
Example
place
phone call
cellular
network
user
receive
phone call
place
conference
call
receive
additional
call
use
scheduler
<<extend>>
<<extend>>
Cellular Telephone

Use Case Description
Each use case may include all or part of the following:
 Title or Reference Name - meaningful name of the UC
 Author/Date - the author and creation date
 Modification/Date - last modification and its date
 Purpose - specifies the goal to be achieved
 Overview - short description of the processes
 Cross References - requirements references
 Actors - agents participating
 Pre Conditions - must be true to allow execution
 Post Conditions - will be set when completes normally
 Normal flow of events - regular flow of activities
 Alternative flow of events - other flow of activities
 Exceptional flow of events - unusual situations
 Implementation issues - foreseen implementation problems

Example- Money Withdraw
• Use Case: Withdraw Money
• Author: PKD
• Date: 11-09-2013
• Purpose: To withdraw some cash from user’s bank account
• Overview: The use case starts when the customer inserts his card
into the system. The system requests the user PIN. The system
validates the PIN. If the validation succeeded, the customer can
choose the withdraw operation else alternative 1 – validation
failure is executed. The customer enters the amount of cash to
withdraw. The system checks the amount of cash in the user
account, its credit limit. If the withdraw amount in the range
between the current amount + credit limit the system dispense
the cash and prints a withdraw receipt, else alternative 2 –
amount exceeded is executed.
• Cross References: R1.1, R1.2, R7

• Actors: Customer
• Pre Condition:
– The ATM must be in a state ready to accept transactions
– The ATM must have at least some cash on hand that it can dispense
– The ATM must have enough paper to print a receipt for at least one
transaction
• Post Condition:
– The current amount of cash in the user account is the amount before
the withdraw minus the withdraw amount
– A receipt was printed on the withdraw amount
– The withdraw transaction was audit in the System log file

Typical course of events

• Alternative flow of events:
– Step 3: Customer authorization failed. Display an error
message, cancel the transaction and eject the card.
– Step 8: Customer has insufficient funds in its account.
Display an error message, and go to step 6.
– Step 8: Customer exceeds its legal amount. Display an
error message, and go to step 6.
• Exceptional flow of events:
– Power failure in the process of the transaction before step
9, cancel the transaction and eject the card

 One method to identify use cases is actor-based:
- Identify the actors related to a system or organization.
- For each actor, identify the processes they initiate or participate in.
 A second method to identify use cases is event-based:
- Identify the external events that a system must respond to.
- Relate the events to actors and use cases.
 The following questions may be used to help identify the use
cases for a system:
- What are tasks of each actor ?
- Will any actor create, store, change, remove, or read information in the
system ?
- What use cases will create, store, change, remove, or read this information ?
- Will any actor need to inform the system about sudden, external changes ?
- Does any actor need to be informed about certain occurrences in the system ?
- Can all functional requirements be performed by the use cases ?

Use Case Diagram

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Use Case Diagram