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UML Use Case Modeling:
Use Case Diagram / Use Case Description
6 January 2016
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Use Case Approach
library system
Provide lending
services
Library user
Control user
administration
Books
database
Library staff
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Use Case Modeling
• Use Case model – A model that describes the functional
requirements of a system in terms of use cases.
• A use case model partitions system functionality into
– requirements / goals / transactions (‘use cases’) that are
– meaningful to users (‘actors’);
and is shown on a use case diagram
• System developers and customers/end-users discuss a
use case model. {In an iterative process, this lead to a requirement
specification on which all agree.}
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UML Views
vocabulary
functionality
system assembly
configuration management
Component
view
Design view
Use Case
view
behaviour
performance
scalability
throughput
Concurrency
view
logical
Deployment
view
physical
system topology
distribution
delivery
installation
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Use Case Diagram Definition
A diagram that shows a set of use cases and actors
and their relationships.
Use cases represent system functionality, the requirement
of the system from the user’s perspective.
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Use Case Definition
• Fowler:
– A use case is a typical interaction that a user has with a system in
order to achieve some goals.
– A use case is a description of a set of sequence of actions,
including variants, that a system performs to yield an observable
result of value to an actor.
• Cockburn:
– A use case describes a system’s behavior.
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Use Case
•
•
•
A use-case is a set of sequences of
actions a system performs that yield an
observable result of value to a particular
actor.
A use-case describes a requirement for
the system, that is, what it should do, but
not how it should do it.
UseCaseName
A use-case is a set of scenarios tied
together by a common user goal.
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Actor 1of2
•
An actor is someone or something that
interacts with the system. It is who or
what uses the system.
– Could be human beings, other systems, timers,
hardware devices, etc.
•
•
Actors that stimulate the system are the
initiators of events are called primary
actors (active); Actors that only receive
stimuli from the system are called
secondary actors (passive).
ActorName
An actor is a role that a user plays with
respect to the system.
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Actor 2of2
•
An actor communicates with the system
by sending and receiving messages.
– Who/ what will be interested in the system?
– Who/what will want to change or interface with
the system?
– Who/want information from the system?
ActorName
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System Boundary
•
Represents the boundary
between the (physical) system
and the actors who interact
with the (physical) system.
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Use Case Diagram
A diagram that shows the relationships among actors and use
cases within a system.
Financial Trading System
Set Limits
Update Accounting
Accounting System
Analyze Risk
<<include>>
Price Deal
<<include>>
Trading Manager
Value Deal
Capture Deal
Trader
Salesperson
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Include (Uses) Relationship
• Include : this relationship is used when there is a common
chunk of behaviour across more than one use case.
• Primary use case includes the functionality of included use
case.
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Use Case Relationships
<<extend>>
Place Order
<<include>>
Supply Customer
Data
<<include>>
Request Catalog
<<include>>
Order Product
Arrange Payment
generalization
These use cases
are varieties of
Arrange Payment
Cash Payment
Credit Payment
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Generalization Relationship
• Generalization is used when there is one use case similar
to another.
• Inheriting parent behaviour, adding and overriding with the
child’s behaviour.
• Sub use case inherits behaviour and semantics from
super use cases.
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Use Case Relationships
<<extend>>
Place Order
<<include>>
Supply Customer
Data
<<include>>
Request Catalog
<<include>>
Order Product
Arrange Payment
generalization
These use cases
are varieties of
Arrange Payment
Cash Payment
Credit Payment
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Use Case Relationships
condition: {user request catalog}
extension point: more requests
Place Order
___________
Place
Order
more requests
<<include>>
Supply Customer
Data
<<include>>
<<extend>>
Request Catalog
<<include>>
Order Product
Arrange Payment
generalization
These use cases
are varieties of
Arrange Payment
Cash Payment
Credit Payment
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Extend Relationship
• Extend is used to add behaviour to the primary use case
at certain extension points.
• A use case is optionally extended by functionality of
another use case.
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Use Case Diagram Guidelines
• Use cases should ideally begin with a verb – i.e. “Generate
report”. Use cases should not be open ended.
• Avoid showing communication between actors, and actors
should be named singular.
• Use case diagrams does not show sequence.
• Generally the use of include and extend is discouraged
because they add unnecessary complexity to a use diagram.
• Since the primary purpose of use cases is to show user
centered functionality, the precedence of use cases is less
important.
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D2D example
• D2D is a commercial online dating service
• Requirements
– Interest
– Subscribe
• Request for a subscription
• Cancel a subscription
– Profiles
• Inspect a profile
• Modify a profile
– Messages
– News
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D2D Example
• D2D is a commercial online dating service
• Requirements
– Interest
– Subscribe
• Request for a subscription
• Cancel a subscription
D2D
Request for
subscription
Visitor
Inspect profile
– Profiles
• Inspect a profile
• Modify a profile
– Messages
– News
Modify profile
Subscriber
Cancel subscription
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Primary Use Cases : Examples
Request for
subscription
Visitor
Visitor
Modify profile
Inspect profile
Subscriber
Subscriber
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Separation
• If there are many requirements (also called processes in this
stadium); a requirement can be managed separately.
• In the case of D2D Profiles:
– Inspect a profile
• Look for a profile
• Consult a profile
– Modify a profile
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Secondary Use Cases : An Example
Use cases that supports the use case request for a
subscription
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Secondary Use Cases : An Example
Use cases that supports the use case request for a
subscription
–
–
–
–
–
Import a subscription
Validate a subscription
Import credit card
Validate credit card
Mail confirmation by e-mail
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Secondary Use Cases : An Example
{uses include / extend relationships}
D2D
Import
subscription
Request for
subscription
Validate
subscription
<<include>>
<<include>>
Visitor
Inspect profile
Request for
subscription
<<include>>
<<include>>
Modify profile Visitor
Validate
creditcard
<<extend>>
Subscriber
Import
creditcard
Cancel subscription
Mail confirmation
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Secondary Use Cases : An Example
{uses generalization relationships}
Renew
subscription
<<include>>
Pay
subscription
D2D
Pay subscription
with Creditcard
Pay subscription via
Collection
Pay subscription via
Account
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Use Case Diagram – secondary actor
Import
subscription
<<include>>
<<include>>
Request for
subscription
Visitor
<<include>>
Validate
subscription
Import
creditcard
<<include>>
<<extend>>
Validate
creditcard
Credit card
company
Mail confirmation
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Question?
Timer
Which use case is not valid?
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Question?
Originating from UML SIG – UML
Lecture series;
APIIT Asia Pacific Institute of
Information Technology
What’s wrong?
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Question?
WHY?
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Use Case Description1of2
A use case can be described by a use case text (also
called use case specification), including the next
characteristics:
–
–
–
–
Name: the name of the use case concisely
Actors: the involved actors
Precondition: condition of the system at the start of the use case
Stepwise description (flow of events / pathway): interaction
between system and actor(s)
– Exception: exceptional cases
– Result: post condition of the system
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Use Case Description2of2
A use case description serves as a bridge between
stakeholders of a system and the development team.
Systems analyst produce use
case diagram & use case text in
consultation with end users
Use Case
Diagram
Derived from UML SIG – UML
Lecture series;
APIIT Asia Pacific Institute of
Information Technology
Use Case
Specification
Programmers look at
uses case text to
understand complete
requirements
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Use Case Text example from Inspect a profile
Look for profile
Inspect
preferences
<<include>>
Subscriber
<<extend>>
Inspect profile
<<extend>>
Inspect photo
<<extend>>
Mail message
Visitor
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Use Case Text example from Inspect a profile
Use case ‘mail a message’
•
•
•
•
Name
mail a message
Actors
subscriber
Precondition profile is known, actor is logged in
Description 1. get the profile
2. show web page
3. actor types in a new message
4. actor confirms mailing the message
5. application (d2d) sends message to profile
6. actor receives confirmation of sending a message
•
Result
message mailed to profile; or actor has canceled
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Scenario
A scenario is a sequence of steps describing an
interaction between a user and a system.
– A scenario is an instance of a use-case.
– A scenario describes a possible interaction with the system.
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Scenario for use case ‘log in subscriber’
Description
Chosen scenario
1.
2.
3.
4.
5.
6.
7.
Number of valid logins < 3.
Show web page.
Actor types in login name and
password.
Actor confirms.
Login is valid.
Mark actor as subscriber.
8.
Validate number of invalid logins .
If number of invalid logins more than 2, stop.
Show web page.
Actor types in login name and password.
Actor confirms.
Application validates login.
If login valid
7.1 mark actor as subscriber.
If login invalid
8.1 raise the number of invalid logins.
8.2 repeat from step 1.
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Scenario example 1 of 2
• Consider a Web-based on-line store, we might have a
‘Buy a Product’ scenario that would say this :
– The customer browses the catalogue and
adds desired items to the shopping basket.
– When the customer describes the shipping and credit card
information and confirms the sale.
– The system checks the authorization on the credit card and
confirms he sale both immediately and with a follow-up mail.
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Scenario example 2 of 2
Buy a Product
Main Success Scenario:
1.
2.
3.
4.
5.
6.
7.
8.
Customer browses through catalog and selects items to buy
Customer goes to check out
Customer fills in shipping information (address; next-day or 3-day delivery)
System presents full pricing information, including shipping
Customer fills in credit card information
System authorizes purchase
System confirms sale immediately
System sends confirming email to customer
Extensions:
3a: Customer is regular customer
3a1:
System displays current shipping, pricing, and billing information
3a2:
Customer may accept or override those defaults, returns to MSS at step 6
6a: System fails to authorize credit purchase
6a1:
Customer may re-enter credit card information or may cancel
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Template of use case text
Name
Name used to refer to a use case.
Actors
All actors involved.
Preconditions
Condition of the system at the start of the
use case.
Description
A complete stepwise description of the
interaction between system and actor(s).
Extensions
Lists the extension points currently
defined for this selected Use Case.
Exceptions
Special and/or unexpected exceptional
cases.
Result
Condition of the system at the end of the
use case.
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NS Ticket machine – a use case approach
Destination
Purchase Ticket
Traveler
Maintenance
basic data
Take ticket
NS
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NS Ticket machine – use case diagram
Buy OV ticket
<<extend>>
<<include>>
Buy NS ticket
Traveler
Pay ticket
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NS Ticket machine – use case text
Use Case
Buy OV Ticket
Actors
Traveller
Preconditions
Traveller has a valid pass
Description
1.
2.
3.
4.
5.
6.
7.
Ticket device expects destination code
Traveller enters destination code
Extension point: NS ticket
Ticket device checks code and calculates the charge. Shows destination code & fare.
Activates ticket machine for paying
Traveller pays (use case: Pay ticket)
Ticket device print and supplies ticket
Traveller takes ticket
Extension
Destination code = NS station.
3a. Ticket device expects ticket type
3b. Traveller enters Single/Return, Discount Y/N, Class
Exceptions
Traveller interrupt the interaction or walk away
Traveller enters an incorrect destination code
Payment is not finished off successful
Result
Traveller has ticket.
(NS can look forward to the payment)
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Study matter
• Martin Fowler
UML distilled , 2nd / 3rd edition – UML beknopt
Addison Wesley
• Grady Booch, James Rumbaugh, Ivar Jacobson
The Unified Modeling Language User Guide, 2nd edition
Addison Wesley
• Sander Hoogendoorn
Pragmatisch modelleren met UML 2.0
Addison Wesley
{ some slides are based from here}
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