Functional Requirements – Use CasesFunctional Requirements – Use Cases

Sriram Mohan/Steve Chenoweth

(Chapters 14 , 21 – Requirements Text)

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What is a Functional Requirement?What is a Functional Requirement?

Functional requirements specify particular behaviors of a system.

E.g., Suppose your “system” acts on “food” –

“Cook food” is “functional.”

Vs How well it cooks, or how fast, or how easily is not.

Why?

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What is a Use Case?What is a Use Case?

A sequence of actions a system performs that yield an observable result of value to a particular actor

Sequences of actions Performed by system of interest Observable result of value to a particular actor

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Benefits – Requirements ManagementBenefits – Requirements Management

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 ?

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Benefits – Development Life Cycle

Use cases become the vehicle for the following activities:

◦ Development of test plans for acceptance testing

◦ Creation of interaction design specifics, simply by adding detail to the use cases about “how” the actions will be done

◦ The basis for discovering a great OO design, based on the actors and their actions

Use Case TemplateUse 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

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Use Case Model - Development StepsUse 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

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1. Identify the Actors1. 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?

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2. Identify the Use Cases2. 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?

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2. Identify the Use Cases2. Identify the Use Cases

Give a descriptive name:◦ Start with an action verb

◦ Describes goal or intent Give a one-sentence description

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3. Identify Actor/Use Case Relationships3. Identify Actor/Use Case Relationships

Draw a diagram showing relationships between actors and use cases

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Eat food

Buy foodParent Child

4. Outline Use Cases4. Outline Use Cases

Describe sequence of events in basic flow (sunny day scenario)

Describe sequences of events in alternate flows (rainy day scenarios)

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5. Refine Use Cases5. Refine Use Cases

Describe sequences of events for flows Describe pre-conditions Describe post-conditions Fill in special requirements

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Pre and Post ConditionsPre and Post Conditions

What is a pre-condition? What is a post-condition?

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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 TemplateUse Case Template

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Microwave ExampleMicrowave Example

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User

Cook Food

Cook Food Use Case – Slide 1 of 4Cook 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

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Cook Food Use Case – Slide 2 of 4Cook 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 tells microwave to start

4. Unit cooks food

5. Unit indicates it is done

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Cook Food Use Case – Slide 3 of 4Cook 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

4. Make sure you detail the alternate flows completely

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Cook Food Use Case – Slide 4 of 4Cook 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◦ Unit should indicate remaining time to finish while

cooking◦ Default power setting should be "high"

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How do the use case and the storyboard fit?How do the use case and the storyboard fit?

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

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Extending Use CasesExtending Use Cases

Extend an existing use case instead of redefining it

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Microwave ExtensionMicrowave Extension

User

Cook Food

Slice Food

<<extend>>

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Including Use CasesIncluding Use Cases

Frequent sequences of events may be defined as use cases

Including a use case is like calling a subroutine

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Microwave InclusionMicrowave Inclusion

User

Cook Food

Set Timer

<<include>>

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Cook Food InclusionCook 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

RFC 2119

Will, Shall, Must Should May

Is there a difference?

Extra CreditExtra Credit

Can all functional requirements be specified using use cases? Explain

Turn in your Answer using Angel (Lessons – Extra Credit – Week 3- Use Case Extra Credit)

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Exam 1Exam 1

Managing Software Requirements (Second Edition)◦ Chapters 1 – 14(Except Chapter 11)

◦ Chapter 21 Interaction Design – Beyond Human Computer

Interaction◦ Chapter 7, 8 &11

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In-Class ActivityIn-Class Activity

Develop use cases for the following features of the student feedback project

1. Instructors must be able to create and assign quizzes to their students

2. Instructors may analyze student responses to a quiz

3. Students must be able to provide anonymous feedback

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