Functional Requirements – Use Cases (Chapters 14, 21) Sriram Mohan 1

What is a Functional Requirement? Functional requirements specify particular behaviors of a system. 2

What is a Use Case? A sequence of actions a system performs that yield and observable result of value to a particular actor Sequences of actions Performed by system of interest Observable result of value to a particular actor 3

Benefits Easy to write and read Think from the perspective of an user Provides a clear idea of the “what” and the “how” User involvement Use cases tell a better requirement story Typically developers are encouraged and required to write use cases. Why ? 4

Use Case Template A. Name B. Brief description C. Actors D. Basic flow E. Alternate flows F. Pre-conditions G. Post-conditions H. Other stakeholders I. System/sub-system J. Special requirements 5

Use Case Model - Development Steps 1. Identify the actors 2. Identify the use cases 3. Identify actor/use case relationships 4. Outline use cases 5. Refine use cases 6

1. Identify the Actors Who uses the system? Who gets/provides information from/to system? Who supports the system? What other systems interact with this system? 7

2. Identify the Use Cases What are the intentions of each actor with respect to the system? ◦ What are they going to use the system for? ◦ Does the actor provide some information? ◦ Does the actor need to be informed of something? 8

2. Identify the Use Cases Give a descriptive name: ◦ Start with an action verb ◦ Describes goal or intent Give a one-sentence description 9

3. Identify Actor/Use Case Relationships Draw a diagram showing relationships between actors and use cases 10 Eat food Buy food Parent Child

4. Outline Use Cases Describe sequence of events in basic flow (sunny day scenario) Describe sequences of events in alternate flows (rainy day scenarios) 11

5. Refine Use Cases Describe sequences of events for flows Describe pre-conditions Describe post-conditions Fill in special requirements 12

Pre and Post Conditions What is a pre-condition? What is a post-condition? 13

A. Name B. Brief description C. Actors D. Basic flow E. Alternate flows F. Pre-conditions G. Post-conditions H. Other stakeholders I. System/sub-system J. Special requirements Use Case Template 14

Microwave Example 15 User Cook Food

Cook Food Use Case – Slide 1 of 4 A. Name: Cook Food B. Brief description: User places food in microwave and cooks it for desired period of time at desired power level. C. Actors: User 16

Cook Food Use Case – Slide 2 of 4 D. Basic flow: 1.User opens door and places food in unit 2.User enters time for cooking 3.User pushes start button 4.Unit cooks food 5.Unit beeps 17

Cook Food Use Case – Slide 3 of 4 E. Alternate flows 1.User cancels time before starting 2.User cancels cooking before finished 3.User selects reduced power level before pushing start button 18

Cook Food Use Case – Slide 4 of 4 F. Pre-conditions ◦ Unit is plugged in ◦ Unit is in ready state G. Post-conditions ◦ Food is cooked or user cancelled operation H. Special requirements ◦ Timer should display remaining time to finish while cooking ◦ Default power setting should be "high" 19

How do the use case and the storyboard fit? 20

How do you know you have collected enough use cases? 21

22 Extending Use Cases Extend an existing use case instead of redefining it

23 Microwave Extension User Cook Food Slice Food >

24 Including Use Cases Frequent sequences of events may be defined as use cases Including a use case is like calling a subroutine

25 Microwave Inclusion User Cook Food Set Timer >

26 Cook Food Inclusion D. Basic flow: 1.User opens door and places food in unit 2.User performs Set Timer use case 3.User pushes start button 4.Unit cooks food 5.Unit beeps

Extra Credit Can all functional requirements be specified using use cases? Explain Turn in your Answer using Angel(Lessons – Extra Credit – Week 03- Use Case Extra Credit) 27

Exam 1 Managing Software Requirements(Second Edition) ◦ Chapters 1 – 14 ◦ Chapter 21 Interaction Design – Beyond Human Computer Interaction ◦ Chapter 11 28