A use case models the interactions between external actors and a system to achieve goals. It captures functional requirements from the user's perspective and involves users in requirements gathering. A use case consists of actors and use cases, which describe a sequence of steps in the interaction. Scenarios provide specific examples of a use case. Use cases help test and communicate system functionality.

1. USE CASE MODELLING
• A use case is a scenario that describes the
use of a system by an actor to accomplish a
specific goal.
• An actor is a user playing a role with respect
to the system.
- people, other systems.
• Scenario
A sequence of steps that describe the
interactions between an actor and the
system.
• The use case model consists of the collection
of all actors and all use cases.

2. Use cases help ..
· Capture the system's functional requirements
from the users' perspective
· Actively involve users in the requirements-
gathering process
· Provide the basis for identifying major classes
and their relationships
· Serve as the foundation for developing system
test cases

3. USE CASE MODELLING
-functional reqts., analysis phase
- what a system does: functions represented as use cases
- Actor: external agent that interacts with the system,
exchanges info. with the system (user, sub-system, etc.)
- a role played by user
Note: a use case represents a complete functionality.
– view of system behavior from an external person’s viewpoint
– effective tool for validating requirements
– an effective communication tool
– basis for a test plan
– basis for user manual
Developing the use cases in not difficult; ensuring that you
have them all is murder.

4. • Use Case Diagrams
– Actor
– Line: actor communicates with or is associated
with use-case
Customer Loses a Tape

5. • Use Case relationships:
– <<uses>>: one use case always involves the
steps of another
– <<extends>>: under certain conditions, a use case
follows a variant
Customer
Loses a Tape
Buy a Tape
<<uses>>
Customer
VIP Loses a Tape
<<extends>>

6. Goals of use cases
• Interactions that provide value to actors
• No implementation specific language
– No assumptions about how the use case may be realized in code or
user-interface
– Note: use-cases drive the whole life-cycle, and they get refined –
implementation specific use-cases
• User-appropriate level of detail
– General at requirements gathering stage
• User-appropriate volume
– Large systems: no more than 70-80 use cases
– Small number of use cases – forces abstraction

7. Use case scenarios
• a realization of a use case.
• Instance of an use case that effectively tests one path through a use
case
• To demonstrate whether a use case accurately reflects user needs
• useful during testing
Example:
Use case name: Determine benefits eligibility for enrollee
Steps:
1. This use case starts when the social worker enters the enrollee’s name and
employment situation.
2. This use case ends when the system responds with a determination of
whether the enrollee is eligible for benefits and the financial extent of benefits.
Alternative path:
In step 1, if the enrollee has applied for benefits previously, based on the
enrollee’s own disclosure, the social worker enters the enrollee’s name to search
for his or her previous records

8. Use case scenario - example
Example of scenario
1. The social worker asks Edward Trueman if he has applied previously
for and/or received benefits. And Mr. Trueman replies that he has
applied previously.
2. The social worker provides Mr. Trueman’s name as search criterion
3. The system provides Mr. Trueman’s previous records, which state
that he applied for benefits on Dec 9th
, 1997, and was determined to
be ineligible on Dec 9th
1997 because of his current part-time
employment status at Boeing Aerospace in the capacity of assembly
line worker.

9. Registration for
special class
Class
registration
Prereq courses
not completed
Student Billing
Student
Bursar’s
office
Registration
Clerk
Instructor
<<Extends>> <<Extends>>
Use-Case Diagram
Extends: extension to or variation of a use-case that exists in its own right

10. Order Food
Hire Employee
Reorder
supplies
Produce
mgt. reports
Track sales
and inv. data
<<uses>>
<<uses>>
Customer
Applicant
Supplier
Service Person
Manager
Uses: factors common behavior amongst multiple use-cases into a
generalized use-case.

11. Step 1: Identifying Actors and Use Cases
– From context diagram, workflow diagram
Step2:Construct Use Case Model
– System scope and boundary in terms of use cases and actors
– partitioned into sub-systems
Step 3:Use Case sequence of actions
Step4: Identifying use case dependencies
Step5: Use case alternate course of actions
Step6: Finding Potential Objects
– Nouns in use case
Step7: Selecting proposed Objects
• Class Diagram (Object Association Model, Object
Relationship Model)

12. • Finding the actors
- Ask client and domain experts how system will
be used
- Who will perform the obvious tasks?
Secondary tasks of maintenance and
administration? Interact with other systems?
- Clear and differentiated names (eg. manager
vs supervisor)

13. • Recording the use cases
- For each actor, what interactions /”results” they
require of the system –each is a use case
• Not overly precise yet, just note them down
– What tasks does the actor want the system to perform
– What information must the actor provide to the system
– Are there events that the actor must tell system about
– Does actor need to be informed when something
happens
– Does actor help initialize or shut down the system

14. Example: video store system Actor: Customer
- What tasks does the actor want the system to perform?
- Find movie to rent, rent tape, return tape, reserve tape
- What information must the actor provide to the
system?
- Name, address, membership#, film name
- Are there events that the actor must tell system about?
- Change of address
- Does actor need to be informed when something
happens?
- Reserved tape is ready to be rented
- Does actor help initialize or shut down the system
- no

15. Example: video store system
Resulting use cases:
• Customer joins and provides contact information
including name, address, phone#, credit information,
spouse and kids
• Customer browses system looking for a tape to rent
• Customer comes to store looking for a specific tape
to rent
• Customer rents a tape
• Customer returns a tape
• Customer reserves a tape
• Customer is contacted when a reserved tape is ready
Note: simple phrases, without much details initially.

16. • Finding the actors
- Ask client and domain experts how system will
be used
- Who will perform the obvious tasks?
Secondary tasks of maintenance and
administration? Interact with other systems?
- Clear and differentiated names (eg. manager
vs supervisor)

17. • Recording the use cases
- For each actor, what interactions /”results” they
require of the system –each is a use case
• Not overly precise yet, just note them down
– What tasks does the actor want the system to perform
– What information must the actor provide to the system
– Are there events that the actor must tell system about
– Does actor need to be informed when something
happens
– Does actor help initialize or shut down the system

18. Example: video store system Actor: Customer
- What tasks does the actor want the system to perform?
- Find movie to rent, rent tape, return tape, reserve tape
- What information must the actor provide to the
system?
- Name, address, membership#, film name
- Are there events that the actor must tell system about?
- Change of address
- Does actor need to be informed when something
happens?
- Reserved tape is ready to be rented
- Does actor help initialize or shut down the system
- no

19. Example: video store system
Resulting use cases:
• Customer joins and provides contact information
including name, address, phone#, credit information,
spouse and kids
• Customer browses system looking for a tape to rent
• Customer comes to store looking for a specific tape
to rent
• Customer rents a tape
• Customer returns a tape
• Customer reserves a tape
• Customer is contacted when a reserved tape is ready
Note: simple phrases, without much details initially.

20. Example: video store system
– Other actors:
• Clerk adds a new film to the system
• It is time to order more films – manager wants to know
which films are popular so as to get extra copies
• Store orders 10 new copies of film; when they arrive,
clerk adds them to system and puts them on shelf
• Manager wants to know if he is making money
• thinking of these may lead to some more customer use
cases:
- Customer wants to know new movies in the store.

21. Example: video store system
• Use cases from attributes of “things”
– tapes have actors, film name, director, release date
– Customer wants to find every movie starring a
specific actor
– Customer wants to find movies with same director as
the last film she rented
– Manager wants to put together list of movies rated
‘G’.
• Use cases to manage the attributes:
– Clerk adds new film to system
– Clerk removes obsolete film from system
– Clerk updates information about a film

22. Example: video store system
• These use cases can remind us of similar
responsibilities for customers:
– Clerk adds customer to the system
– Clerk removes customer account from system
– Clerk updates customer’s account

23. • Use case name, description
Example: Customer Loses a Tape
The customer reports to the clerk that he has lost a
tape. The clerk prints out the rental record and asks
customer to speak with the manager, who will
arrange for the customer to pay a fee. The system
will be updated to reflect lost tape, and customer’s
record is updated as well. The manager may
authorize purchase of a replacement tape.

24. • Scenarios: a use case scenario shows the flow of
events in a particular instance of a use case.
– focussed on the business problem, not the solution
- shows most common situation
- can have greater or less detail as required to understand flow
of interactions and events
- also consider exceptional rather than the normal situations.
• Scenario guidelines
– how does the scenario begin? what causes it to end?
- what is the distinction between what the actors do and how the
system responds
- what feedback will the actor receive?
- which activities may repeat, and what causes them to stop?
– Is there conditional branching in the flow of the scenario?

25. • Formal description of use cases:
- Use case name
- Actors, brief description
- Actions taking place
- scenario – flow of events
- Some use cases have multiple scenarios to
explore various contingent activities
- Preconditions –before the use case can begin
– Eg. for Lost a Tape use case, customer must be
member and must have rented a tape.
- Post-conditions: state of system and perhaps for
actors, after the use case is completed

26. Member
Services
Department
Past
Member
Club
Member
Request
Membership rpts
Submit
subscription
renewal
Create new
subscription
program
Submit New
Subscription
Send subscription
renewal offer
Send new
subscription offer
Potential
Member
Member
Services System
Submit Regular
Order
Request Sales
Reports
Submit
Promotion Order
Marketing Department
Create New
Seasonal
Promotion
Create New
Monthly
Promotion
Request
Promotion
Reports
Send Club
Promotion
Membership
System
Orders
SubSystem
Promotions
SubSystem

27. Send subscription
renewal offer
subscription
renewal
Create new
subscription program
Send new
subscription
offer
Submit New
Subscription
depends on
depends on
depends on
depends on
Submit
Promotion Order
Send Club Promotion
Create New
Seasonal
Promotion
Create New
Monthly
Promotion
depends on
OR
depends on
depends on
Request
Membership
rpts
Request
Promotion Reports
Request Sales
Reports
Submit Regular
Order
Member Services System Use Case Dependency Diagram

28. ACTORS USE CASE
Club Member Initiates Submit Promotion Order
Submit Regular Order
Potential Member Initiates Submit New Subscription
Past Member Initiates Submit Subscription Renewal
Membership Services Dept. Initiates Request Membership Reports
Marketing Department Initiates Create New Monthly Promotion
Create New Seasonal Promotion
Create New Subscription Program
Request Promotion Reports
Request Sales Reports
Membership Services System Initiates Send New Subscription Offer
Send Club Promotion
Send Subscription Renewal

29. USE CASE NAME Submit Promotion Order
ACTOR Club Member
DESCRIPTION Describes the process when a club member submits a club promotion
order to either indicate the products they are interested in ordering or
declining to order during this promotion
1. This use is initiated when the club member submits the promotion
order to be proceeded
2. The club member's personal information such as address is validated
against what is currently recorded in member services
3. The promotion order is verified to see if product is being ordered
4. The club member's credit status is checked with Accounts Receivable
to make sure no payments are outstanding
5. For each product being ordered, validate the product number
6. For each product being ordered, check the availability in inventory
and record the ordered information which includes "quantity being
ordered" and give each ordered product a status of "open"
7. Create a Picking Ticket for the promotion order containing all ordered
products which have a status "open"
Normal Course
8. Route the picking ticket to the warehouse
PRECONDITION Use case send club promotion has been processed
POST CONDITION Promotion order has been recorded and the picking ticket has been
routed to the warehouse
ASSUMPTIONS

30. USE CASE NAME Submit Promotion Order
ACTOR Club Member
DESCRIPTION Describes the process when a club member submits a club promotion order to either indicate
the products they are interested in ordering or declining to order during this promotion
1. This use is initiated when the club member submits the promotion order to be proceeded
2. The club member's personal information such as address is validated against what is
currently recorded in member services
3. The promotion order is verified to see if product is being ordered
4. The club member's credit status is checked with Accounts Receivable to make sure no
payments are outstanding
5. For each product being ordered, validate the product number
6. For each product being ordered, check the availability in inventory and record the ordered
information which includes "quantity being ordered" and give each ordered product a status
of "open"
7. Create a Picking Ticket for the promotion order containing all ordered products which have a
status "open"
8. Route the picking ticket to the warehouse
NORMAL COURSE
2. If the club member has indicated an address or telephone number change on the promotion
order, update the club member's record with the new information
3. If the club member is not ordering product at this time, modify the promotion order's status
to be "closed" and modify the selection of the month ordered product's record to have a
status of "rejected", then cancel the transaction
4. If Account Receivable returns a credit status that the customer is in arrears, invoke abstract
use case Send Order Rejection Notice Modify the promotion's order's status to be "on hold
pending payment"
5.
a) If the product number is not valid, create an Order Error Report containing the club
member's information, the promotion order information, and the product number in
error. Each completed report will be routed to a Member Services clerk for
resolution.
b) If the club member is not ordering the selection of the month, modify the ordered
product's record to have a status of "rejected"
6. If the product being ordered is not available, record the ordered product information which
includes "quantity being ordered" and give a status of "backordered"
ALTERNATE COURSE
7. If there are no ordered product records with a status "open", cancel the transaction
PRECONDITION Use case send club promotion has been processed
POST CONDITION Promotion order has been recorded and the picking ticket has been routed to the warehouse
ASSUMPTIONS

31. POTENTIAL OBJECT LIST
Club Member
Potential Member
Past Member
Member Services Department
Marketing Department
Member Services System
Member Address
Promotion Order
Product
Product Inventory
Order Quantity
Ordered Product
Credit Status
Payments
Ordered Product Status
Picking Ticket
Warehouse
Member Telephone Number
Selection of Month
Transaction
Accounts Receivable
Promotion Order Status
Order Error Report
Member Services Clerk

32. POTENTIAL OBJECT LIST REASON
Club Member √ Type of "MEMBER"
Potential Member √ Type of "MEMBER"
Past Member √ Type of "MEMBER"
Member Services Department X Not relevant for current project
Marketing Department X Not relevant for current project
Member Services System X Not relevant for current project
Member Address X Attribute of "MEMBER"
Promotion Order √ Result of an event named "PROMOTION"
√ Type of "MEMBER ORDER"
Product √ "PRODUCT"
Product Inventory X Attribute of "PRODUCT"
Order Quantity X Attribute of " MEMBER ORDER"
Ordered Product √ "PRODUCT ON ORDER"
Credit Status X Attribute of "MEMBER"
Payments X Out of Scope
Ordered Product Status X Attribute of "PRODUCT ON ORDER"
Picking Ticket X Potential interface item
Warehouse X Not relevant for current project
Member Telephone Number X Attribute of "MEMBER"
Selection of Month √ Type of "TITLE"
Transaction X Not relevant for current project
Accounts Receivable X Not relevant for current project
Promotion Order Status X Attribute of "MEMBER ORDER"
Order Error Report X Potential interface item
Member Services Clerk X Not relevant for current project

33. New
Mem
bership
Plan
&
Sub. Offer
Sales
and
Prom
otion
Reports
New
M
onthly
OR
Seasonal Prom
otion
Club promotion
Promotion order
regular order
Subscription renewal
offer
Subscription renewal
Club
Member
Past
Member
Potential
Member
Order to be filled
Membership
Reports
Warehouse
Member Services Dept. Marketing Dept.
A/C Receivable
DB
Member credit status
Subscription Offer
New Subscription
Member Services
Context Model