Ivan MarsicRutgers University

LECTURE 1: IntroductionLecture time: 1 hr. 20 min.

Course Information

• Web: http://www.ece.rutgers.edu/~marsic/Teaching/SE

• Lecture Notes:http://www.ece.rutgers.edu/~marsic/books/SE

• Textbooks (see more on the course website)– Bruegge & Dutoit: Object-Oriented Software Engineering: Using UML, Patterns and

Java, Third Edition, Prentice Hall, 2010. | ISBN 0-13-6061257– Miles & Hamilton: Learning UML 2.0, O’Reilly Media, 2006. ISBN: 0-596-00982-8

• Teaching Assistant:Swapnil Mhaske <smhaske@eden.rutgers.edu>

2

Team Projects

• Form teams of 6 (± 1?) studentsDEADLINE: Friday, January 25, 2013After that, teams assigned randomly

• Project Ideas:http://www.ece.rutgers.edu/~marsic/books/SE/projects

• No more than two (2) groups working on the same project

• One (1) new project allowed• Email your project idea ASAP, before proposal is due, for feedback

3

Personal Health Monitoring Devices

4

Available budget:$500

To do:1. Search the Web for devices and apps that you would like to work with2. Email the components list with costs+websites

Project Deliverables

5

Item Due date

Iterat.

#1

1.   Proposal January 29 2.   First report   (Specification only)      • Part 1 (Statement of Work & Requirements)      • Part 2 (Functional Requirements Spec & UI)      • Full Report #1

 February 12February 18February 22

3.   Second report   (Design only)      • Part 1 (Interaction Diagrams)      • Part 2 (Class Diagram and System Architecture)      • Full Report #2

 March 1March 8March 15

4.   First demo April 2 ► ... Ite

r #2

5.   Third report   (All reports collated) April 27 6.   Second demo May 1 ► ...

7.   Electronic Project Archive May 3

Team Project Grading

35pts

26pts

12 p

100

Team 3

21 p

50 pts

70

Team 2

30pts

100

Team 1

30pts

30pts

Earned points

Project grade

21 pts

TeamProjectgrade

Member ID

Earnedpoints

Adjustedpoints

Normalizedpoints

T1 100%

M1,1 30 30 (30/35 * 100) = 86

M1,2 30 30 (30/35 * 100) = 86

M1,3 30 30 (30/35 * 100) = 86

T2 70%M2,1 21 (21 * 0.7) = 14.7 (14.7/35 * 100) = 42

M2,2 50 (50 * 0.7) = 35 100

T3 100%

M3,1 21 21 (19/35 * 100) = 60

M3,2 12 12 (12/35 * 100) = 34

M3,3 35 35 100

M3,4 26 26 (26/35 * 100) = 74

Introduction: Software is Complex

• Complex complicated

• Complex = composed of many simple parts

related to one another

• Complicated = not well understood, or explained

Complexity Example:Scheduling Fence Construction Tasks

Setting posts[ 3 time units ]

Cutting wood[ 2 time units ]

Painting[ 5 time units for uncut wood;

4 time units otherwise ]

Nailing[ 2 time units for unpainted;

3 time units otherwise ]

Setting posts Nailing, Painting

Cutting Nailing

…shortest possible completion time = ?

8[ “simple” problem, but hard to solve without a pen and paper ]

More Complexity

Suppose today is Tuesday, November 29

What day will be on January 3?

[ To answer, we need to bring the day names and the day numbers into coordination, and for that we may need again a pen and paper ]

The Role of Software Engg. (1)

CustomerCustomerProgrammer

A bridge from customer needs to programming implementation

First law of software engineeringSoftware engineer is willing to learn the problem domain(problem cannot be solved without understanding it first) 10

The Role of Software Engg. (2)

11

Customer:Requires a computer system to achieve some business goalsby user interaction or interaction with the environmentin a specified manner

System-to-be

Software-to-be

System-to-be

Software-to-beUser

Software Engineer’s task:To understand how the system-to-be needs to interact withthe user or the environment so that customer’s requirement is metand design the software-to-be

Programmer’s task:To implement the software-to-bedesigned by the software engineer

Environment

May be thesame person

Example: ATM Machine

Bank’sremote

datacenter

Bankcustomer

ATM machine

12 34

5 67 890

12 34

5 67 890

12 34

5 67 890

Communication link

Understanding the money-machine problem:

12

How ATM Machine Might Work

Window clerk

Bookkeeper

Safe keeper

Datacenterliaison

Dispenser

Safe

Cash

Transactionrecord

Phone

Speakerphone

Bank’sremote

datacenter

Domain Model

How may I help you?

Customer

Domain model created with help of domain expert

13

Cartoon Strip: How ATM Machine Works

B

Verify this

account

B

Verify this

account

C Verify account

XYZ

XYZ valid. Balance:

$100

C Verify account

XYZ

XYZ valid. Balance:

$100

D

Account valid.

Balance: $100

D

Account valid.

Balance: $100

G Record $60 less

G Record $60 less

A Enter your PIN

Typing in PIN number

…

A Enter your PIN

Typing in PIN number

…

E How may I help you?

Withdraw $60

E How may I help you?

Withdraw $60

F Release $60

Dispense$60

F Release $60

Dispense$60

H

Please take your cash

Dispensing!H

Please take your cash

Dispensing!

14

Software Engineering Blueprints

Specifying software problems and solutions is like cartoon strip writing

Unfortunately, most of us are not artists, so we will use something less exciting:UML symbols

However …

15

Second Law of Software Engineering

• Software should be written for people

first

– ( Computers run software, but hardware quickly

becomes outdated )

– Useful + good software lives long

– To nurture software, people must be able to understand

it

16

Software Development Methods

Method = work strategy The Feynman Problem-Solving Algorithm:

(i) Write down the problem (ii) think very hard, and (iii) write down the answer.

Waterfall Unidirectional, finish this step before moving to the next

Iterative + Incremental Develop increment of functionality, repeat in a feedback loop

Agile User feedback essential; feedback loops on several levels of

granularity

17

Waterfall Method

Deployment &Maintenance

Requirements

Design

Implementation

TestingWaterfallmethod

18

Unidirectional, no way backfinish this step before moving to the next

UML – Language of Symbols

«interface»BaseInterface

+ operation()

Actor

ClassName

# attribute_1 : int# attribute_2 : boolean# attribute_3 : String

+ operation_1() : void+ operation_2() : String+ operation_3(arg1 : int)

Software Class

Three commoncompartments:

1. Classifier name

2. Attributes

3. Operations

Comment

Class1Implement

+ operation()

Class2Implement

+ operation()

Software Interface Implementation

Interaction Diagram

doSomething()

instance1 : Class1 instance5 : Class2 instance8 : Class3

doSomethingElse()

doSomethingYetElse()

Inheritancerelationship:BaseInterfaceis implementedby two classes

Stereotype «» provides additional info/ annotation/ explanation

19

UML = Unified Modeling Language

Online information:http://www.uml.org

Understanding the Problem Domain

• System to be developed

• Actors

– Agents external to the system

• Concepts/ Objects

– Agents working inside the system

• Use Cases

– Scenarios for using the system

20

ATM: Gallery of Players

Actors (Easy to identify because they are visible!)

Bank’s remotedatacenter

System(ATM machine)

Bank customer

12

345

678

90

12

345

678

90

Bank’s remotedatacenter

System(ATM machine)

Bank customer

21

Gallery of Workers + Things

Concepts (Hard to identify because they are invisible/imaginary!)

Window clerk Bookkeeper Safe keeperDatacenterliaison

Dispenser

Safe CashTransactionrecord

TelephoneSpeakerphone

22

Use Case: Withdraw Cash

B Verify account

XYZ

XYZ valid. Balance:

$100

B Verify account

XYZ

XYZ valid. Balance:

$100

12 34

5 67 890

12 34

5 67 890

C How may I help you?

Withdraw $60

12 34

5 67 890

12 34

5 67 890

C How may I help you?

Withdraw $60

12 34

5 67 890

12 34

5 67 890

A Enter your PIN

Typing in PIN number

…

12 34

5 67 890

12 34

5 67 890

A Enter your PIN

Typing in PIN number

…

D

12 34

5 67 890

12 34

5 67 890

Please take your cash

Collecting cash …

D

12 34

5 67 890

12 34

5 67 890

Please take your cash

Collecting cash …

E XYZ withdrew

$60

Acknowledged

E XYZ withdrew

$60

Acknowledged

23

Window clerk

Bookkeeper

Dispenser

Transactionrecord

Speakerphone

How may I help you?

Customer

Draftsman

Solution modification

Solution modification

How ATM Machine Works (2)Domain Model (2)

Alternative solution

How ATM Machine Works (3)Domain Model (3)

Remotebank

Window clerk

Bookkeeper

Dispenser

Transactionrecord

Speakerphone

How may I help you?

Customer

Courier

Solution modification

Solution modification

Alternative solution

Which solution is the best or even feasible?

Rube Goldberg Design

26

Garage door opener

Actual Design

27

Rail with a belt or chain

Operator (includes motor and radio control mechanism)

Garage door

Safety reversing sensor

Pressing of a button on the remote control transmitter (1)authenticates the device & activates the motor in the operator (2).The motor pulls the chain (or belt) along the rail (3) and windsthe torsion spring (4).The torsion spring winds the cable on the pulleys (or drums) (5)on both sides of the door. The cables lift the door, pushing the different sections of the doorinto the horizontal tracks (6)At the same time, the trolley (or traveler) (7) moves along the rail (3)and controls how far the door opens (or closes),as well as the force the garage door exerts by way of the curved door arm (8)

Remote control transmitter 2

1

3

4 5

5

6

6

7

8

Software Measurement

• What to measure?

– Project (developer’s work),

for budgeting and scheduling

– Product,

for quality assessment

28

Formal hedge pruning

29

Sizing the Problem (1)

Size( ) = 10

Size( ) = 7

Size( ) = 4

Size( ) = 3

Size( ) = 4

Size( ) = 2

Size( ) = 4

Size( ) = 7

Step 2:Estimate relative sizes of all parts

Step 1: Divide the problem into small & similar parts

Sizing the Problem (2)

• Step 3: Estimate the size of the total work

Total size = points-for-section i (i = 1..N)

• Step 4: Estimate speed of work (velocity)

• Step 5: Estimate the work duration

Travel duration = Path size

Travel velocity

Sizing the Problem (3)

• Advantages:

– Velocity estimate may need to be adjusted (based on

observed progress)

– However, the total duration can be computed quickly

(provided that the relative size estimates of parts are

accurate – easier to achieve if the parts are small and

similar-size)

Exponential Cost of Estimation

Estimation cost

Est

imat

ion

accu

racy

100%

Improving accuracy of estimation beyond a certain point requires huge

cost and effort (known as the law of diminishing returns)

In the beginning of the curve, a modest effort investment yields huge

gains in accuracy33

Estimation Error Over Time

Time

Estimationerror

CompletionStart

The cone of uncertainty starts high and narrows down to zero as the project approaches completion.

Requirements Design ImplementationImplementation

Agile Project Effort Estimation

35Time

2nd iteration n-th iteration

Estimated completion date

Items pulled by the team into an iteration

1) Prune Section 8 3.5 days (7pts)

Work backlog

2) Prune Section 7 2 days (4pts)

3) Prune Section 6 1 day (2pts)

4) Prune Section 5 2 days (4pts)

1st iteration

5) Prune Section 4 1.5 days (3p)

6) Prune Section 1 2 days (4pts)

7) Prune Section 2 3.5 days (7p)

Work items

8) Prune Section 3 5 days (10p)

21 days

5 daysList prioritized by the customer

Estimated work duration

Good Shape(Low branches get sun)

Poor Shape(Low branches

shaded from sun) Heading back not recommended as it alters the natural shape of the shrub

Remove dead wood

Remove water spouts and suckers

Snow accumulates on broad flat tops

Straight lines require more frequent trimming

Peaked and rounded tops hinder snow accumulation

Rounded forms, which follow nature’s tendency,

require less trimming

Measuring Quality of Work

36

Concept Maps

Proposition

Concept Relation Concept

1. I have friend

2. friend engages in coding

3. coding constructs a

program

4. program

is new

SENTENCE: “My friend is coding a new program”

translated into propositions

Search the Web for Concept Maps

I

friend

have

coding

engages in

program

constructs a

newis

37

Useful tool for problem domain description

Case Study: Home Access Control

• Objective: Design an electronic system for:– Home access control

• Locks and lighting operation

– Intrusion detection and warning

System

Lock Photosensor Switch

Light bulb

Alarm bell

1

2

3

4

5

X

Y

1

2

3

4

5

X

Y

38

Case Study – More Details

System

Lock Photosensor Switch

Light bulb

Alarm bell

1

2

3

4

5

X

Y

1

2

3

4

5

X

Y CentralComputer

Backyard doors:External &

Internal lock

Front doors:External &

Internal lock

CentralComputer

Backyard doors:External &

Internal lock

Front doors:External &

Internal lock39

Know Your Problem

1

9

7

8

6

2

3

54

7 Thumb-turn

1 Lock case

2 Latch bolt

3 Dead bolt

9 Left hand lever

8 Lock cylinder

6 Protective plate

5 Strike box

4 Strike plate

Mortise Lock Parts

1

2

3

4

5

X

Y

1

2

3

4

5

X

Y

40

Concept Map for Home Access Control

tenant

key

can be prevented by enforcinglock opened

wishes

causes

enters

valid key invalid key

can be

dictionary attack

may signal

upper bound on failed attempts

burglar launches

41

States and Transition Rules

locked unlocked

IF validKey THEN unlock

IF pushLockButton THEN lock

IF timeAfterUnlock ≥ max{ autoLockInterval, holdOpenInterval } THEN lock

IF validKey AND holdOpenInterval THEN unlock

42… what seemed a simple problem, now is becoming complex