--- title: "Importance of use case diagram" subject: "Object Oriented Analysis and Design" chapter: 2 key: "semester_6/object_oriented_analysis_and_design:use-case-diagram-importance-uml" source: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/use-case-diagram-importance-uml site: BCT Engineering --- # Importance of use case diagram Object Oriented Analysis and Design · Chapter 2: Object Oriented Analysis - Asked in: 2073 Bhadra, 3+3 marks - Video: [Use Case Diagram in UML | Software Engineering](https://www.youtube.com/watch?v=Hj6Lkoi_VoM) — Gate Smashers - Page: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/use-case-diagram-importance-uml - Whole chapter: https://www.bctengineer.com/md/semester_6/object_oriented_analysis_and_design/chapter-2 ## Question What makes the use-case diagram as an important in UML diagrams? Illustrate your argument with a model use-case diagram for a particular scenario. ## Short answer The use-case diagram captures functional requirements from user’s viewpoint, defines system boundary, and drives development and testing. For an Online Library, Member (Search, Reserve, Renew Book) includes Login; Librarian (Issue, Return Book) with extend Charge Fine. ## Answer #### Why the use case diagram is important A **use case diagram** shows the actors outside the system and the functions (use cases) the system offers them. It is important because: 1. It captures **functional requirements** from the **user's viewpoint**, in a form that customers and non-technical people can understand. 2. It fixes the **scope and boundary** of the system (what is inside, what is outside). 3. It is the **starting point** of the whole OO process: classes, sequence diagrams, test cases and user manuals are derived from the use cases (use case driven development). 4. It helps in **planning and prioritising**: iterations are planned by use cases. 5. It serves as a **contract** between customer and developers and a base for acceptance testing. 6. It is simple, with only few symbols (actor, use case, association, include, extend, generalization). #### Model use case diagram: Online Library ```text +-----------------------------+ | Online Library System | [Member] ----|-( Search Book ) | [Member] ----|-( Reserve Book ) | [Member] ----|-( Renew Book ) | | |include | | v | | ( Login ) | [Librarian] -|-( Issue Book ) | [Librarian] -|-( Return Book ) | | ^ | | |extend | | ( Charge Fine ) | +-----------------------------+ ``` **Scenario:** A member logs in and searches a book; if unavailable, he reserves it. The librarian issues and receives the book; if the return is late, the optional use case `Charge Fine` extends `Return Book`. `Renew Book` includes `Login`. The diagram thus gives a single clear picture of who uses the library system and what the system provides. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Whose viewpoint does a use case diagram capture functional requirements from? A. The database administrator B. The compiler C. The tester only D. The user (non-technical people can understand it) Answer: D. It expresses functional requirements from the user's viewpoint in a form customers can understand. (Key point: Viewpoint of use cases) 2. How does a use case diagram help define scope? A. It fixes what is inside and outside the system boundary B. It lists all the code files C. It shows the network topology D. It shows memory use Answer: A. Actors outside and use cases inside the boundary define the scope. (Key point: System boundary and scope) 3. Why is the use case diagram the starting point of the OO process? A. It is drawn last B. Classes, sequence diagrams, test cases and manuals are derived from use cases C. It replaces all other diagrams D. It contains the source code Answer: B. Later artifacts are derived from use cases, and iterations are planned by use cases. (Key point: Use case driven development) 4. In the Online Library example, how is Charge Fine related to Return Book? A. Return Book includes Login B. Charge Fine always runs C. Charge Fine is an optional extension used when the return is late D. Charge Fine is an actor Answer: C. Fine is charged only for late returns, so it extends Return Book. 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