1. Intro: Use Case and Use Case Diagram Documentation

2. Use Case A use case is a contract of an interaction between the system and an actor. Use Case Diagram: an integration of use cases

3. Use Case Diagram A use case diagram illustrates a set of use cases for a system, the actors, and the interactions between actors and use cases. A graphical overview of the functionality provided by a system in terms of actors, their goals (represented as use cases), and any dependencies between those use cases.actorsuse cases

4. Use Case Diagram Objectives 1.Create a semi-formal model of the functional requirements 2. Analyze and define: Scope External interfaces Scenarios and reactions

6. What makes a good Use Case Diagram? Lack of ambiguity - Each requirement must be interpreted in a single manner. Completeness - The collection of all use cases is everything that can be done to/with the system. Consistency - Requirements should not conflict with each other. If there are, tradeoffs must be detected and discussed. Avoid design - Requirements should raise a need, not answer it.

7. Construct a Use Case Diagram

8. Finding actors External objects that produce/consume data: 1.Must serve as sources and destinations for data 2.Must be external to the system Humans Machines External systems Sensors

9. Actor Relationships – Generalization/Specialization Define hierarchy for actors Notation The child actor inherits all use- cases associations Should be used if (and only if), the specific actor has more responsibility than the generalized one (i.e., associated with more use-cases)

10. Association: Actor and Use Case Solid line: Interaction between actors and use case Arrowhead (optional) Control flow Initial invocation, primary actor

11. Use Case Relationships Goal: enable flexibility in requirements specification 1.Isolating functionality 2.Enabling functionality sharing 3.Breaking functionality into manageable chunks Relationships 1.Include 2.Extend 3.Generalization

12. Include Goal: 1.Decomposing complicated behavior 2.Centralizing common behavior the behavior of the included use case is inserted into the behavior of the including use case - The first use case often depends on the outcome of the included use case.

13. Extend the behavior of the extension use case may be inserted in the extended use case under some conditions Note the direction of the arrow The base use-case does not know which use-case extends it

15. Generalization use case may have common behaviors, requirements, constraints, and assumptions with a more general use case.

16. Example: Cellphone Company System Hint - Actors: Phones, Phone Companies

18. Writing Use Cases Name: Actors: Descriptions: – Precondition – Main flow – Sub flow – Alternative flow

19. Precondition What the system needs to be true before running the use-case. – User account exists – User has enough money in her account – There is enough disk space

20. Main flow The success scenario is the main story-line of the use-case Assumption: everything is okay, no errors or problems occur, and it leads directly to the desired outcome of the use-case It is composed of a sequence of subflows Example: Step 1: Administrator enters course name, code and description (interaction) Step 2: System validates course code Step 3: System adds the course to the db and shows a confirmation message (interaction)

21. Branches: If the user has more than 10000$ in her account, the system presents a list of commercials Otherwise… Repeats: User enters the name of the item he wishes to buy System presents the items User selects items to buy Systems adds the item to the shopping cart User repeats steps 1-4 until indicating he is done Sub flow

22. Used to describe exceptional functionality Examples: 1.Errors 2.Unusual or rare cases 3.Failures 4.Starting points 5.Endpoints 6.Shortcuts Alternative flows

23. Write Include in User Case Reference

24. Write Exclude in Use Case Extension Point

25. Use Case sample

26. Include Concept

28. Extend Concept

31. Generalization Concept

32. Effective Use Cases Only one side (system or actor) is doing something in a single step Write from an “objective” point of view using active tense Any step should lead to some progress

33. Effective Use Cases “Get the amount form the user and give him the money” “User click the enter key” ATM

34. 1.No actor 2.Too many user interface details “User types ID and password, clicks OK or hits Enter” 3.Very low goal details User provides name User provides address User provides telephone number Effective Use Cases – Common Mistakes

35. From Use-Case to Use-Case Diagrams Top down ? Starting with an overview of the system, and then splitting Use-cases Bottom up ? Starting with throwing all scenarios on the page, and then combining them: Most of the analysis process are actually combined

36. Common Rules Number Limit: The diagram should have between 3 to 10 base use-cases. No more than 15 use cases (base + included + extending). ---- If the dependency between two parts of a use-case is weak, they should be divided. Abstraction: All use-cases should be in similar abstraction levels. Size: Use cases should be described in half a page or more. - split using include/exclude

37. When we are done When every actor is specified. When every functional requirement has a use- case which satisfies it. A tractability matrix can help us determine it:

38. Use Case and Use Case Diagram a Summary When to use What is Use Case and Use Case Diagram How to Construct Use Case Diagram How to Write Use Case Questions?