Based-on slide Ivan Marsic

Rekayasa Perangkat Lunak

Untuk SISTEM KOMPUTER
Kuliah 1: Pendahuluan

Mohammad Iqbal
Based-on slide Ivan Marsic

Course Information
 Textbooks
– 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

2

Pendahuluan : Software itu
Kompleks
• Complex  complicated
• Complex = composed of many simple parts
related to one another

• Complicated = not well understood, or explained

Contoh Kompleksitas:
Skedul Tugas Membangun Konstruksi Pagar

Setting posts
[ 3 time units ]

Cutting wood
[ 2 time units ]

Nailing
[ 2 time units for unpainted;
3 time units otherwise ]

Painting
[ 5 time units for uncut wood;
4 time units otherwise ]

Setting posts  Nailing, Painting
Cutting  Nailing

…shortest possible completion time = ?
[  “simple” problem, but hard to solve without a pen and paper ]

4

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 ]

Peranan Software Enggineer (1)
A bridge from customer needs to programming implementation

Customer
Programmer

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

6

Peranan Software Enggineer (2)
Customer:
Requires a computer system to achieve some business goals
by user interaction or interaction with the environment
in a specified manner

System-to-be

User

Software-to-be

Environment

Software Engineer’s task:
To understand how the system-to-be needs to interact with
the user or the environment so that customer’s requirement is met
and design the software-to-be
May be the
same person

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

7

Contoh: Mesin ATM
Understanding the money-machine problem:

7

4

1

0

2
5 3
8 6
9

ATM machine

Communication link

Bank’s
remote
datacenter

Bank
customer
8

Strategi Pemecahan-Masalah
Divide-and-conquer:
 Identify logical parts of the system that each
solves a part of the problem
 Easiest done with the help of a domain expert
who already knows the steps in the process
(“how it is currently done”)
 Result:
A Model of the Problem Domain
(or “domain model”)
9

Bagaimana Mesin ATM bekerja
Domain Model

How may I

help you?

Transaction
record
Cash

Bookkeeper

Speakerphone

Safe keeper

Safe
Phone

Window clerk
Datacenter
liaison

Dispenser

Customer

Bank’s
remote
datacenter

10

Komik

A

: Bagaimana Mesin ATM bekerja
Enter
your PIN

C

B

Verify
account
XYZ

D

Verify
this
account
Typing in
PIN number
…

E

How may
I help
you?

Withdraw
$60

Account
valid.
Balance:
$100

XYZ valid.
Balance:
$100

F

G

Release
$60

Dispense

$60

Record
$60 less

Dispensing!

H
Please take
your cash

11

Cetak Biru Software Engineering
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 …

12

Hukum Kedua 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

13

Metode Pengembangan Software
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
 Continuous user feedback essential; feedback loops on several levels
of granularity
14

Metode Waterfall
Requirements
Design
Implementation

Waterfall
method

Testing

Each activity confined to its “phase”.
Unidirectional, no way back;
finish this phase before moving to the next

Deployment &
Maintenance

15

UML – Bahasa Simbol
UML = Unified Modeling Language
«interface»
BaseInterface
ClassName
# attribute_1 : int
# attribute_2 : boolean
# attribute_3 : String

Three common
compartments:

Actor

1.

Classifier name

2.

Attributes

3.

Operations

+ operation()

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

Class1Implement

Class2Implement

+ operation()

+ operation()

Stereotype
«» provides
additional info/
annotation/
explanation

Inheritance
relationship:
BaseInterface
is implemented
by two classes

Software Class

Comment

Software Interface Implementation

instance1 : Class1

instance5 : Class2

doSomething()

instance8 : Class3

doSomethingElse()

Interaction Diagram
doSomethingYetElse()

Online information:
http://www.uml.org
16

Seberapa Banyak Kita Membuat
Diagram?


Use informal, ad-hoc, hand-drawn, scruffy diagrams
during early stages and within the development team
– Hand-drawing forces economizing and leads to low emotional
investment
• Economizing focuses on the essential, most important considerations
– Prioritize substance over the form

• Not being invested facilitates critique and suggested modifications



– Always take snapshot to preserve records for future

Use standardized, neat, computer-generated diagrams
when consensus reached and designs have “stabilized”

– Standards like UML facilitate communication with broad range of
stakeholders
– But, invest effort to make neat and polished diagrams only when
there is an agreement about the design, so this effort is worth doing
• Invest in the form, only when the substance is worth such an investment
17

Memahami Problem Domain
 System to be developed
 Actors
– Agents external to the system that interact with it

 Concepts/ Objects
– Agents working inside the system to make it function

 Use Cases
– Scenarios for using the system
18

ATM: Gallery of Players

7

4

0

Bank customer

1
8

5

2
9

6

3

System
(ATM machine)

Bank’s remote
datacenter

Aktor (Easy to identify because they are visible!)
19

Gallery of Workers + Tools

Window clerk

Datacenter
liaison

Bookkeeper

Safe keeper

Dispenser

Speakerphone

Telephone

Transaction
record

Safe

Cash

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

20

Studi Kasus : Ambil Uang Cash
A

B

Verify
account
XYZ

Enter
your PIN

7

4

1

0

8

C

How may
I help
you?

2
5 3
6
9

7

4

1

0

XYZ valid.
Balance:
$100

Typing in
PIN number
…

D

7

4

1

0

Collecting
cash …

8

2
5 63
9

Withdraw
$60

E

Please take
your cash

8

XYZ
withdrew
$60

2
5 63
9

Acknowledged

21

Bagaimana ATM Bekerja (2)
Domain Model (2)

Solution
modification

Alternative
solution
How may I
help you?

Transaction
record

Bookkeeper

Speakerphone

Draftsman
Window clerk

Dispenser

Customer

Bagaimana ATM Bekerja (3)
Domain Model (3)

Alternative
solution

Solution
modification
How may I
help you?

Transaction
record

Bookkeeper

Speakerphone

Courier

Window clerk

Dispenser

Customer

Solusi mana yg terbaik atau lebih fisibel ?

Remote
bank

Desain Rube Goldberg
Pembuka Pintu Garasi

24

Desain Aktual
Operator (includes motor and radio control mechanism)

1

2

Remote control transmitter

6
5

3

7
4

Rail with a belt or chain

5
8

6

Pressing of a button on the remote control transmitter (1)

Garage door

authenticates the device & activates the motor in the operator (2).
The motor pulls the chain (or belt) along the rail (3) and winds
the 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 door
into 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),

Safety reversing sensor

as well as the force the garage door exerts by way of the curved door arm (8)   

25

Fisibilitas & Kualitas Desain
 Judging feasibility

or quality of a design
requires great deal of domain knowledge
(and commonsense knowledge!)

26

Pengukuran Software
 What to measure?
– Project (developer’s work),
for budgeting and scheduling

– Product,
for quality assessment

27

Formal hedge pruning

28

Strategi Estimasi Pekerjaan
1.

Make initial guess for a little part of the work

2. Do a little work to find out how fast you can go
3. Make correction on your initial estimate
4. Repeat until no corrections are needed
or work is completed

29

Mengukur Masalah (1)
Step 1: Divide the problem into small & similar parts








Step 2:
Estimate relative
sizes of all parts
Size(  ) = 4



Size(  ) = 7
Size(  ) = 10

Size(  ) = 3







Size(  ) = 4
Size(  ) = 2
Size(  ) = 4
Size(  ) = 7

Mengukur Masalah (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

Mengukur Masalah (3)
• Assumptions:
– Relative size estimates are accurate
• That’s why parts should be small & similar-size!

• Advantages:
– Velocity estimate may need to be adjusted (based on
observed progress)
– However, the total duration can be recomputed quickly
• Provided that the relative size estimates of parts are accurate
—accuracy easier achieved if the parts are small and similar-size

Estimasi Biaya Eksponensial
Estimation accuracy

100%

Estimation cost

 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 accuracy

33

Estimasi Error Over Time
Estimation
error

Requirements

Start

Waterfall Method

Design

Implementation

Completion

Time

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

Estimasi Error Over Time
Estimation
error

Agile Method
Leap in estimation accuracy
because of experience gained
through completion of a part of work

Requirements
Design
Implementation

Start

Requirements
Design
Implementation

Requirements
Design
Implementation

Completion

Time

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

Agile Project Effort Estimation

36

Mengukur Kualitas Pekerjaan

Good Shape
(Low branches get sun)

Snow accumulates
on broad flat tops

Poor Shape
(Low branches
shaded from sun)

Straight lines require
more frequent trimming

Heading back not
recommended as
it alters the natural
shape of the shrub

Peaked and rounded tops
hinder snow accumulation

Remove dead wood
Remove water spouts
and suckers

Rounded forms, which
follow nature’s tendency,
require less trimming

37

Peta Konsep
Useful tool for problem domain description

SENTENCE: “My friend is coding a new program”
translated into propositions

I
Proposition

Concept

Relation

Concept

1.

I

have

friend

2.

friend

engages in

coding

3.

coding

constructs a

program

4.

program

is

new

have
friend
engages in
coding
constructs a
program
is

Search the Web for Concept Maps

new

38

Studi Kasus : Home Access
Control
 Objective:

Design an electronic system for:

– Home access control
• Locks and lighting operation

– Intrusion detection and warning
Alarm bell

System
1
2
3
4
5
X
Y

Light bulb

Lock

Photosensor

Switch

39

Studi Kasus – Detail
Alarm bell

System
1
2
3
4
5
X
Y

Lock

Light bulb

Photosensor

Switch

40

Memahami Problem
Mortise Lock Parts

1 Lock case
4

1

2 Latch bolt
3 Dead bolt

6
2

9

5

4 Strike plate
5 Strike box

3
7

6 Protective plate
7 Thumb-turn
8 Lock cylinder

8

9 Left hand lever

1
2
3
4
5
X
Y

41

Peta Konsep untuk Home Access
Control
tenant
enters
wishes

key
can be
upper bound on failed attempts

lock opened

causes

valid key

invalid key
may signal

burglar

launches

can be prevented by enforcing

dictionary attack

42

Aturan Status dan Transisi
IF validKey AND holdOpenInterval THEN unlock

IF validKey THEN unlock

locked

unlocked

IF pushLockButton THEN lock
IF timeAfterUnlock ≥ max{ autoLockInterval, holdOpenInterval } THEN lock

… what seemed a simple problem, now is becoming complex

43