1. Chapter 5:
Use Cases
Chapter 6 & 25 in Applying UML and Patterns Book.

2. Overview What use cases are and how to write them.
Different format of use cases.
How to draw a use case diagram.
Extend and include use cases.

3. By the end of this chapter, you will..
Understands the use case diagram and the different relationship types inside the use case diagram.
Understands the meaning of “Use Case”.
Understands the different methods in writing the use cases.

4. Capturing functional requirements with use case diagram
It describes the main system functions from the standpoint of an external observer.
Used during requirements elicitation to represent external behavior.
It emphasize on what the system does rather than how it.
It is created during the early stages of a project – during the analysis phase rather than during the design phase.
It provides a high-level view of what the system does and who uses it.
It provides the basis for determining the user interfaces (UIs) to the system.

5. Example: Use Case Diagram ATM Banking System

6. Use Case Diagram Any use case diagram should contain: Actor(s).
Use cases.
Associations/Relationships among actors and use cases.

7. Use Case Diagram Actor
Actors are drawn as stick persons with the role of the actor written below.
Actor names are unique typically represent the role that an actor plays with respect to the system.
Is someone (e.g. human beings) or something (e.g. other objects or systems) that interact with the system.
Is entity external to the system who participates in the story of the use case (receive or input), such as a person, computer system or organization.
Example: a library clerk, cashier, customer, Passenger, GPS satellite, bank, customer department.
Actor role name

8. Use Case Diagram Use Case
Use cases are drawn as ellipses with the name of the use case written inside the ellipse.
Use case name typically consists of an active verb and one or more nouns that concisely describe the system function modeled.
Use case

9. Use Case Diagram Use Case
Use Cases: is a collection of related scenarios that describe actors using a system to support a goal.
Scenario (Use Case instance):
Is a possible example of what happens when an actor interacts with the system.
Represents a unit of functionality that the system provides.
Contains a specific sequence of actions and interactions between actors and the system under discussion.
Example: the scenario of entering book information into the catalog, or buying items at a store, or using an ATM.

10. Use Case Diagram Association/Relationship
Actors are connected to the use case(s) with which they interact by a line, which represents the relationship between the actor(s) and the use case(s).
One actor may be associated with one or more use cases.
One use case may be associated with one or more actors.

11. Example 1: Use Case Diagram Banking System

12. Example 2: Use Case Diagram Registration System

13. Example 3: Use Case Diagram Library System

14. Activity: Use Case Diagram
Possible use cases for an online ticket reservation website:
Sign in, sign out, register, add post, delete post.
Sign in, sign out, Book flight, cancel flight, buy ticket.
Sign in, sign out, rate service, buy item.

15. Use Case(s)
Each use case have an associated behavior specification which describes the sequence of actions making up a use case scenario.
Use case behavioral description has two formats:
Expanded Use Case
High Level Use Case
Describes a process in details. It has an additional section not present in HL.
Describes a process very briefly, usually in 2 or 3 sentences.
Purpose: Intention of the use case.
Type: 1- Primary, Secondary or Optional. 2- Essential or Real.
Cross References: Related use cases and system functions.
Typical course of actions: describes in detail the conservation of interaction between the actors and the system.
It consists of :
Use Case: Use case name.
Actors: List of actors (external agents) indicating who initiates the use case.
Description (Success scenario): Narrative description of the process.

16. High Level Use Case Format: HL Example 1: Buy Items
Use Case: Buy Items
Actor: Customer(initiator) , Cashier
Description (Success Scenario): A customer arrives at a checkout with items to purchase. The Cashier records the purchase items and collects payment. On completion, the Customer leaves with the items.

17. High Level Use Case Format: HL Example 2: Library - Add Resources
Use Case: Add Resources
Actor: Librarian
Description (Success Scenario): The use case begins when the Librarian receives new resources (books and videos) to add to the catalog. The title, call number, and other information are recorded. Then the resources are placed on a shelf organized by resource type and call numbers.

18. Expanded Use Case Types Primary - Secondary - Optional
Represents processes that may not be tackled.
Describes a rare, unusual, or exceptional processes.
Ex: Request for stocking new product.
Describes a major, common process.
Ex: Buy items.

19. Expanded Use Case Types Primary - Secondary - Optional
Book ticket use cases is a:
Primary
Secondary
Optional

20. Expanded Use Case Types Essential - Real
Abstract level use cases:
Real
Essential
Concretely describes the process in terms of its real current design, committed to specific input and output Technology.
Design-oriented.
Expressed in terms of the solution. Ex: screen shots of windows, entry into input fields, and so forth.
The essence of the process.
Analysis-oriented.
Expanded use cases that are expressed in an ideal form free of technology and implementation details.
HL are always essential.
Expresses process relatively independent of HW/SW solutions.

21. Expanded Use Case Types Essential - Real
Examples of essential vs. real types:
Real
Essential
The Librarian uses the laser wand to scan the bar code for the call number, which is transmitted to the computer.
The Librarian records the call number.
Ex1
The Account Holder inserts the card into the ATM card reader. He is prompted to enter his PIN (see screen shot 4), which he inputs with a numeric keypad.
The Account Holder identifies himself to the ATM.
Ex2

22. Expanded Use Case Format Example: Buy Items with Cash
Use Case: Buy Items with Cash.
Actor: Customer (initiator), cashier.
Purpose: Capture a sale & its cash payment.
Overview (Success Scenario): A customer arrives at a checkout with items to purchase. The Cashier records the purchase items and collects a cash payment. On completion, the Customer leaves with the items.
Type: Primary.
Cross References: Functions R1.2,…

23. Expanded Use Case Format Example: Buy Items with Cash (cont.)
System Response
Actor Action
1. This use case begins when a Customer arrives at the POST checkout with items to purchase.
3. Determines the item price and adds the item information to the running sales transaction. The description and price of the current item are presented.
2. The Cashier records the identifier from each item. If there is more than one of the same item, the Cashier can enter the quantity as well.
5. Calculate and presents the sale total.
4. On completion of item entry, the Cashier indicates to the POST that item entry is complete.
6. The Cashier tells the Customer the total.

24. Expanded Use Case Format Example: Buy Items with Cash (cont.)
System Response
Actor Action
7. The Customer gives a cash payment possibly greater than the sale total.
9. Shows the balance due back to the Customer & generate a receipt.
8. The Cashier records the cash received amount.
11. Logs the completed sale.
10. The Cashier deposits the cash received & extracts the balance owing. The Cashier gives the balance owing, & the printed receipt to the Customer.
12.The Customer leaves with the items purchased.
Alternatives: Line 2. Invalid identifier entered. Indicate errors.
Line 7. Customer didn’t have enough cash. Cancel sales transaction.

25. Expanded Use Case - Essential vs
Expanded Use Case - Essential vs. Real Types Example 1: Buy Items with Cash
Essential use case
Real use case
System Response
Actor Action
Determines the item price & adds the item information to the running sales transaction. The description and the price of the items are presented.
This Cashier records the identifier for each item.
System Response
Actor Action
Display the item price & adds the item information to the running sales transaction. The description & price of the current item are displayed in
Textbox 2 of Window1.
For each item, the Cashier types in the UPC field of Window1. They then press “Enter Item” button with the mouse or Enter key.

26. Expanded Use Case - Essential vs
Expanded Use Case - Essential vs. Real Types Example 2: ATM Withdraw Cash
Essential use case
Real use case
System Response
Actor Action
Presents options.
This Customer identifies themselves.
System Response
Actor Action
2. Prompts for PIN.
1. The Customer inserts his card.
4. Display options menu.
3. Enter PIN on keypad.

27. Identifying Use Cases Either by: Example: Type 2: Event based
Type1: Actor based
Identify the external events that a system must respond to.
Relate the events to actors and use cases.
Identify the actors related to an organization.
For each actor, identify the processes they initiate or participate in.
Log in, Cash out.
Cashier
Buy items, Refund items.
Customer

28. Use Cases = Processes
A use case describes a process, such as business process.
A process describes, from start to finish, a sequence of events, actions and transactions required to produce or complete something of value.
Example:
Withdraw cash from an ATM.
Order a product.
Register for courses at a school.
Check the spelling.
Handle a call.

29. Decision Point & Branching
A Use case may contain decision points such as in Buy Items, the customer may choose to pay via cash, credit or check.
If one of them is the typical case (usual), then the typical case is the one written in Typical course of events, and the other alternatives should be written in the Alternatives section.
If all the alternatives are equal in their likelihood, (like the payment types), write in the main section of Typical course of events a branch event, that indicates that the possible branches are written in subsections.
Then write a subsection for each branch, again using Typical course of events.
If subsections have alternatives, write them in an Alternatives section.

30. Decision Point & Branching Example: Buy items
Section: Main
System Response
Actor Action
1. This use case begins when a Customer arrives at POST checkout with items to purchase.
2. …..
3. Customer chooses payment type:
a. If cash payment, see section pay by Cash.
b. If credit payment, see section pay by Credit.
c. If check payment, see section pay by Check.
4. Logs the completed sale. 5. Print the receipt.
6. The cashier gives the receipt to the customer.
7. The customer leaves with the items.

31. Decision Point & Branching Example: Buy items (cont.)
Section: Pay by cash
System Response
Actor Action
1. The customer gives a cash payment- possible greater than the sale total.
2. The Cashier records the cash tendered.
3. Shows the balance due back to the Customer.
4. The Cashier deposits the cash received and extracts the balance owing.
The Cashier gives the balance owing to the
Customer.
Alternatives: Line 4. Insufficient cash in drawer to pay balance. Ask for cash from supervisor or ask Customer for a payment closer to sale total.

32. Plan and Elaborate Phase Steps
Define system function.
Define system boundary, actors & use cases.
HL use cases.
Draw use case diagram.
Expand critical use cases (Essential / Analysis).
Real use case (Design).
Rank use case (not discussed).

33. System Administrators
Example 1 2- Define actors and use cases:
Log in, Cash out.
Cashier
Buy items, Refund items.
Customer
Start up, Shut down.
Manager
Add new users.
System Administrators

34. Example 1 (cont.) 3- Use cases in HL format:
Use Case: Buy Items
Actors: Customer (initiator), Cashier
Type: Primary
Description: A Customer arrives at a checkout with items to purchase. The Cashier records the purchase items and collects a payment. On completion, the Customer leaves the store with the items.
Use Case: Start Up
Actors: Manager
Type: Primary
Description: A Manager powers on a POST in order to prepare it for use by Cashiers. The Manager makes sure the date and time are correct, after which the system is ready for Cashiers’ use.

35. Example 1 (cont.) 4- Use cases diagram:

36. Example 1 (cont.) 5- Expand critical use cases:

37. Example 1 (cont.) 5- Expand critical use cases:

38. Example 1 (cont.) 5- Expand critical use cases:

39. Example 2 Use Case: Make a book Entry Use Case: UC1 - Make Book Entry
Actor: Library clerk
Success Scenario:
A library clerk accesses a terminal in order to enter one or possibly many book entries in a database. At the end of every entry, the system displays a confirmation message. At the end of the session the system would display an informative message.

40. Example 2 (cont.)
Use Case Diagram

41. The <<extends>> Relationship
<<extends>> relationships represent exceptional or seldom invoked cases.
A reusable use case (component) that conditionally interrupts (is invoked optionally - like a menu selection in an application) the execution of another use case to augment its functionality.
The functionality in the original problem statement needs to be extended.
The exceptional event flows are factored out of the main event flow for clarity.
The base use case can be executed without the use case extension in extend associations.
The responsibility for deciding when the extending use case should be used lies with the extending use case.
Arrow points to use case being extended.

42. The <<extends>> Relationship
Use cases representing exceptional flows can extend more than one use case.
The direction of an <<extends>> relationship is to the extended use case.
For example: the use case “ReportEmergency” is complete by itself, but can be extended by the use case “Help” for a specific scenario in which the user requires help.

43. The <<extends>> Relationship
Major variation: If you have a major alternative path in the use case, and it’s complex enough to have its own alternative paths, then placing it on your diagram will honestly expose the complexity - which is helpful in costing, assignment and scheduling.
Optional subgoal: If you have parts of the use case that would be optional to implement (or even optional to execute) to meet the actor’s goals, put those parts into their own use case. Doing so clarifies the relationships between actors and their goals. It also emphasizes that you may deliver these optional goals in later releases.

44. The <<extends>> Relationship

45. The <<extends>> Relationship

46. The <<extends>> Relationship

47. The <<extends>> Relationship

48. The <<extends>> Relationship

49. The <<include>> Relationship
<<includes>> relationship represents behavior that is factored out of the use case.
A use case uses another use case (“functional decomposition”).
Used to indicate that one use case includes the functionality of another use case.
A function in the original problem statement is too complex to be solvable immediately.
Describe the function as the aggregation of a set of simpler functions. The associated use case is decomposed into smaller use cases.
A reusable use case (component) that is unconditionally called into the execution of another use case (always included in the process – like running BIOS in a system boot).

50. The <<include>> Relationship
Responsibility for the decision about when to use it lies with the calling use case.
Arrow points to the included use case. The direction of a <<includes>> relationship is to the using use case (unlike <<extends>> relationships).

51. The <<include>> Relationship

52. The <<include>> Relationship

53. The <<include>> Relationship

54. <<extends>> and <<include>> Relationships Summary
Do not try to identify «include» and «extend» relationships in your first cut model.
Use «include» to abstract sequences of steps out of the primary Use Cases that are useful to the analyst to avoid repetitious descriptions.
Use «extend», sparingly, to overlay additional functionality on top of a well-formed Use Case to divide up the complexity of a large and complex Use Case.

55. Generalization/Specialization Relationship
Called inheritance relationship.
Occurs when there is a general sequence of events, but when considering the details, there are many specialised variations of the use case.
Graphically, this is shown by a generalisation line pointing from the specialised use case to the more general use case.

56. Actor Generalization

57. Actor Generalization

58. Actor Generalization