1. ® IBM Software Group © 2006 IBM Corporation Writing Good Use Cases Module 1: Introduction to Use-Case Modeling

2. 2 Objectives  When you complete this module, you should be able to:  Define actor, use case, and use-case model  List the benefits of use cases  Explain how use cases fit into a requirements management process and the software development lifecycle

3. 3 Use cases involve a shift in thinking From a focus on the function of a system To a focus on the value a system must deliver for its stakeholders

4. 4 Actor  An actor represents a role that a human, hardware device, or another system can play in relation to the system  An actor is external to the system  A complete set of actors describes all of the ways in which outside users communicate with the system  Unified Modeling Language (UML) notation for actor: Actor

5. 5 Use case  A use case is…  the specification of a set of actions  performed by a system,  which yields an observable result that is, typically,  of value for one or more actors or other stakeholders of the system. (Unified Modeling Language - UML 2.0)  Used to specify the behavior of a system, without revealing the internal structure of the system Use Case

6. 6 Use cases contain software requirements  Each use case  Is a coherent unit of functionality provided by a system  Describes sequences of actions that the system takes to deliver something of value to an actor  Models a dialog between the system and actors  Is a complete and meaningful flow of events from the perspective of a particular actor

7. 7 Benefits of use cases  Give context for requirements  Put system requirements into logical sequences  Illustrate why the system is necessary  Help verify that all requirements are captured  Are easy to understand  Use terminology that customers and users understand  Tell concrete stories of system use  Verify stakeholder understanding  Aid team communication and understanding  Facilitate agreement with customers  Facilitate the creation of test cases, documentation, and design  Facilitate requirements reuse

8. 8 Who should care about use cases?  Analysts  Customers  Users  Software architects  Designers  Testers  Project managers  Documentation writers

9. 9 Guidelines for when to use use cases Good candidate System with behaviors that can be captured using a sequence of actions Example: Telephone switch System with a lot of externally observable behavior Example: Course Registration System Not a good candidate System with behaviors that cannot be captured using a sequence of actions Example: Compiler software

10. 10 What is NOT a use case  Functional decomposition  User interface specification  System design specifications

11. 11 Use cases and other requirements Design constraints  Operating systems  Environments  Compatibility  Application standards FURPS  Functionality  Usability  Reliability  Performance  Supportability Legal and regulatory requirements  Federal Communication Commission  Food and Drug Administration  Department of Defense  Canadian Standards Association  European Union Directive Use Cases

12. 12 What is a use-case model?  Describes the functional requirements of a system in terms of use cases  Links stakeholder needs to software requirements  Serves as a planning tool  Consists of actors and use cases

13. 13 Capture a use-case model  A use-case model is comprised of: Use-case diagrams (visual representation) Use-case specifications (text representation)

14. 14 Use-case diagram  Shows a set of use cases and actors and their relationships  Defines clear boundaries of a system  Identifies who or what interacts with the system  Summarizes the behavior of the system Use case 1 Use case 2 Use case 3 The System Actor 1 Actor 3 Use case 1 Use case 2 Use case 3 Use case 1 Use case 2 Use case 3 The System Actor 1 Actor 3 Actor 2 Use-case diagram

15. 15 Use-case specification  A requirements document that contains the text of a use case, including:  A description of the flow of events describing the interaction between actors and the system  Other information, such as:  Preconditions  Postconditions  Special requirements  Key scenarios  Subflows Use-case specification

16. 16 Use cases and the requirements management process Find Actors and Use Cases Detail a Use Case IBM ® Rational Unified Process ® (RUP ® ) Requirements Management workflow Outline Use Cases

17. 17 Use cases drive software development Verified byRealized by Implemented by Implementation Model Test Model Design Model Use-Case Model

18. 18 Review  What is an actor?  What is a use case?  What are some of the benefits of using use cases?  What is a use-case model?  What is a use-case diagram?  What is a use-case specification?  How does use-case modeling fit into the requirements management process?  How does use-case modeling fit into the software development lifecycle?

19. 19 Exercise 1: What is a use case?  Given a list of potential use cases, determine which, if any, are use cases.

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