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OOA&D

Use Case Diagrams

USE CASE MODELING 

What is a use case?

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How to draw a use case diagram?

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Relationships between Actors and Use

Cases

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Use case stereotypes (NEW!!)

Review of Use Case Diagrams: 3 Important Terms An actor represents a role, that is, a type of user of the system Student DoHomework Used during requirements elicitation and analysis to represent behavior visible from the outside of the system Use case model : The set of all use cases that completely describe the functionality of the system. A use case represents a class of functionality provided by the system

Actor Student  An actor is a model for an external entity which interacts with the system:  EndUser, Administrator  (^) External system (Another system)  Physical environment (e.g. Weather)  An actor has a unique name and an optional description  Examples:  Student : A studying person  (^) Teaching Assistant : Member of teaching staff who supports the instructor.  Random Number generator Name Optional Description

Use Case DoHomework

• A use case represents a class of functionality provided by the system
• Use cases can be described textually, with a focus on the event flow between actor and system
• The textual use case description consists of 5 parts:
  1. Unique name
  2. Participating actors
  3. Preconditions/post-conditions
  4. Flow of events
  5. Special requirements.(if any)

Use Case To find use cases ask :

• “How does each actor use the system?” and
• “What does the system do for each actor?” 

Always started by an actor

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Always specified from the user point of view

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Naming:

 Verb with an object  e.g. Place Order 

Representation:

 an Oval with name inside Place Order GetStatus OnOrder

Use Case Model Use case diagrams represent the functionality of the system from user’s point of view Actor. Use Case System boundary Classifier

Example of a Use Case Diagram Telephone catalogue Customer Salesperson Shipping Clerk Supervisor Check status Place order Fill orders Establish credit

Example of a Use Case Diagram Move Right Fire Laser View High Scores Play Game Player Move Left

Example: Mail order system

Textual Use Case Description Example

1. Name: DoHomework 2. Participating actor(s): Student 3. Entry condition:  (^) Student received exercise sheet  Student is in good health 4. Exit condition:  (^) Student delivered solution 5. Flow of events: 1. Student fetches the exercise sheet 2. Student reads through the assignments 3. Student processes the assignments and types the solution in his Computer. 4. Student prints out the solution 5. Student delivers the solution in the following exercise 6. Special requirements: None.

Example 

BookStore that sells books and CDs which

provides a web-based selling channel from

which customers can buy its product on the

web.

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Actors:

 Customer − the person who buys products from BookStore ;  Shopkeeper − the person who is responsible for carrying on business in the shop;  System Administrator − the person who manages the web-based system;

Use Cases Find

20 Use case example Use case: ManageBasket ID: UC Actors: Customer Preconditions:

1. The shopping basket contents are visible. Flow of events:
2. The use case starts when the Customer selects an item from the basket.
3. If the Customer selects “delete item”
   1. The system removes the item from the basket
4. If the Customer types a new quantity
   1. The system updates the quantity on the item in the basket. Postconditions :
5. The basket contents have been updated.