02-Introduction to OOAD

8/4/2019 02-Introduction to OOAD

http://slidepdf.com/reader/full/02-introduction-to-ooad 1/82

FALL 2010

FAST National University of Computer and Emerging Sciences Islamabad, Pakistan

OBJECT ORIENTEDANALYSIS AND DESIGN

Instructor : Dr. Arshad AliShahid : Muhammad Ahmed

Lecture : 02

Date : 11th August, 2010

1



OOADFall 2010


INTRODUCTION TOOBJECT ORIENTED

ANALYSIS ANDDESIGN

Session 1



3

Object Oriented Analysis & Design, Fall 2010 © Dr. Arshad Ali Shahid and Muhammad Ahmed

Session Objectives and LearningOutcomes:

What is Object; What is Object-Orientation?

Why OO?

What is OOAD & How to do OOAD?

What are Object Oriented (OO) Methods?

(C++, Java, Oracle??)

What are OO methods used for?

What are the features of OO methods?

How are they different from SSADM?

3



Software Crises

Software Complexity

Why Object-Oriented?4



5


Software Project Failure

1. Problems Faced By The Customers US Internal Revenue System has abandoned its tax system modernization

program after having spent $4 billion;

the state of California spent $1 billion on its non-functional welfare database

system; the £339 million UK air traffic control system was reported as being two years

behind schedule;

a discount stock brokerage company had 50 people working 14 hours or more aday to correct three months of records clerically – the report commented that

the new system had been rushed into operation without adequate testing; in the United Kingdom, a Home Office immigration service computerization

project was reported as having missed two deadlines and was nine months late;

the Public Accounts Committee of the House of Commons (UK) blamedsoftware bugs and management errors for £12 million of project costs in relationto an implementation of a Ministry of agriculture computer system to administer

farm subsidies.

5



6


Software Crises

2. General

H/W advances continue to outpace the pace ofbuilding S/W to tap hardware‘s potential.

Our ability to build S/W could not keep pace withthe growing need of business and market

Demand of highly reliable operations (ticketing,communication, traffic control and power control)of S/W due to our dependency on computer

6



7


Software Crises

3. AN INDUSTRY PERSPECTIVE

Why cost estimations are mostly incorrect?

Why requirements are kept changing

Why does it take so long to get programsfinished?

Why are costs so high?

Why can‘t we find all errors before we give theS/W to our customer?

Why do we have difficulty in measuring progressas S/W is being developed?

7



8


The statistics – Chaos Report

Standish Group – 1995

365 IT executives in US companies in diverse industry segments.

8,380 projects

Project completion

16%

31%

53%

On time, on budget,

with all of the specified

features and functions

Cancelled before they

were completed

delivered and

operational but over-

budget, over-schedule

or with fewer features

and functions thanaverage cost

overrun = 189%

average

timeoverrun

= 222%.

61% of originally specifiedfeatures included

?

In Averages• 189% of original budget

• 221% of original schedule

• 61% of original functionality

8



9


Symptom of Software Crisis

About US$250 billions spent per year in theUS on application development

Out of this, about US$140 billions wasted dueto the projects getting abandoned or reworked;this in turn because of not following best

practices and standards Ref: Standish Group, 1996

9



10


Symptom of SoftwareCrisis…….

10% of client/server apps are abandoned orrestarted from scratch

20% of apps are significantly altered to avoiddisaster

40% of apps are delivered significantly late

Source: 3 year study of 70 large c/s apps 30 European firms.Compuware (12/95)

10



11


Observed Problems

Software products:

fail to meet user requirements

crash frequently

expensive

difficult to alter, debug, enhance

often delivered late

use resources non-optimally

11



OOADFall 2010


GO OBJECT-

ORIENTED – THESOLUTION

But Why Object Oriented!



13


Object Versus Function-Oriented AnalysisDesign

13

Decomposition is the primary strategy to deal with the complexity of S/W project.

Functional decomposition is common in the structured analysis and design. System

can be functionally divided into sub-functions differently by different people.

That’s why it is more commonly called as Analysis & Design.

That’s why a functional hierarchy exists.

Object oriented decomposition has been mentioned in few (Larman) books but

Object identification or classification are most suitable terms used in the OOA. That’s why Object Modeling is more commonly used term as object’s are identified

(they are already there) and modeled in a language rather defined by the analyst.

That’s why decomposition hierarchy does not exist but a collaboration between

objects.

Mp3Recorder

FmPlayer VideoPlayer

Mp3Player

Classification/Decompositionby Objects/concepts

OO A&D

Multimediasystem

Play mp3 Play fmRecord mp3

Decomposition by functions/processesStructured A&D



14


Why Object-Oriented?14



15


What kind of language can alleviate difficulties with communication & complexity hopefully well ?

Why Object-Oriented?......

―The "software crises" came about when people realized the major problems in software development were … caused by communicationdifficulties and the management of complexity‖ [Budd]

The Whorfian Hypothesis:

Human beings … are very much at the mercy of the particular languagewhich has become the medium of expression for their society … the 'realworld' is … built upon the language habits … We cut nature up, organizeit into concepts, and ascribe significances as we do, largely because weare parties to an agreement to organize it in this way … and is codified inthe patterns of our language.

15



16


Why Object-Oriented? – Consider Human Growth & ConceptFormation

Communication & complexity about the problem and the solution, allexpressed in terms of concepts in a language!

But then, What is CONCEPT? [Martin & Odell]

Consider Human Growth & Concept Formation

stage concepts infant the world is a buzzing confusion

very youngage

"blue" "sky― (individual concepts)"blue sky― (more complex concept)hypothesis: humans possess an innate capacity for perception

getting older -> increased meaning, precision, subtlety, ...

the sky is blue only on cloudless days; the sky is not really blueit only looks blue from our planet Earth because of atmospheric effectselaborate conceptual constructs

Concept formation: from chaos to order!

16



17


Why Object-Oriented?- concepts and objects

So, concepts are needed to bring order … into… apparent chaos ! But, What is CONCEPT? [Martin & Odell] [Novak, 1984, Cambridge University Press]

Does Hasham understand the concepts? Do you understand what Hasham understands?

Agree or Disagree?

Study of a first grade class When given a list of

concepts (water, salt water,Oceans, Penguins,...),

Hasham constructed a concept diagram through which he understan ds his world and communicates meaning

17



What is software crisis ? whatare it causes ? explain themwith reasons..

Assignment #118

Font : Verdana, size: 122-3 pages..

Focus on quality content rather than size

Deadline 22nd August

―Google + Wiki + copy, paste Job done‖ = 0 marks



19


What kind of language can be used to create this concept diagram, or Hasham’s mental image?

Why Object-Oriented?… for Conceptual … Modeling Reasons

19

Water

Rivers Oceans

Fish

Penguins

Crocodiles

Fresh water

Salt waterhave

havehave

live in

have

have

Can be

Can be



20


What is a model and why?

A model is a simplification of reality. e.g., a miniature bridge for a real bridge to be built

A model is our simplification of our perception ofreality

A model is an abstraction of something for thepurpose of understanding, be it the problem or asolution. To understand why a software system is needed, what it

should do, and how it should do it.

To communicate our understanding of why, what and how.

To detect commonalities and differences in your

perception, my perception, his perception and her

20



The Solution!

OBJECT ORIENTEDMODELLING

21



22


Object-Oriented Modeling

Attach the behavior and information that isimportant to objects

Associate relations between object to describethe static and dynamic organisation andstructure of real situation

22



23


Object-Oriented Modeling

Tree Next-ToHouse

Lives-inHassan

Drives Car

23

FAST National Uni ersit of Comp ter and Emerging Sciences



OOADFall 2010


WHAT IS OBJECTORIENTATION?



25


What is an Object?25

A structure that has identity and properties and behavior

It is an instance of a collective concept, i.e., a class.

An "object" is anything to which a concept applies, in our awareness Things drawn from the problem domain or solution space.

e.g., a living person in the problem domain, a software component in the solutionspace.



26


An Object

Operations:

Work

Dance

Drive

Jump

Attributes:

Height

Eye colour

Hair colour

Weight

26



27


Relationships

Static :

relations existing over a long time

objects know about each other existence

Dynamic : relations which two objects communicate with

each other

object sending stimuli to other stimuli - events, messages

27

FAST National University of Computer and Emerging Sciences



OOAD

Fall 2010


PRINCIPLES OF

OBJECT ORIENTEDMODELLING

B i P i i l f Obj



29


Object Orientation

E n c a p s

u l a t i o n

A b s t r a c t i o n

P o l y m o

r p h i s m

I n h e r i t a n c e

Basic Principles of ObjectOrientation

29

Ab t ti d



30


Abstraction andEncapsulation Abstraction Focus on the essential Omits tremendous amount of details …Focus on what an object ―is and does‖

Encapsulation a.k.a. information hiding Objects encapsulate: property behavior as a collection of methods invoked by

messages state as a collection of instance variables

30



31


Encapsulation

A concept of ‗Self-containing‘

Information hiding

‗internal‘ structure is hidden from their surroundings

Behavior and information is represented orimplemented internally

Functionality and behavior characterized by‘interfacing’ operations

31



32


What is generalization? Forall x [Car(x) - > …]

Another Example of Abstraction andEncapsulation

<<instanceOf>>

<<instanceOf>>

<<instanceOf>> Class CarAttributes

Model

Location #Wheels =4

Operations Start Accelerate

32



33


Class

What is CLASS ? a collection of objects that share common properties, attributes, behaviorand semantics, in general.

A collection of objects with the same data structure (attributes, statevariables) and behavior (function/operations) in the solution space.

Classification Grouping of common objects into a class

Instantiation. The act of creating an instance.

Class CarAttributes

Model Location #Wheels =4

Operations Start Accelerate

<<instanceOf>>

<<instanceOf>>

<<instanceOf>>

33



34


Class

A class represents a template for severalobjects and describes how these objectsoperate and structured internally

Objects of the same class have the samedefinition both for their operations and theirinformation structure (what about contents ?)

Class contains implementation of objects

34



35


a + b = 10

ClassCourse

PropertiesNameLocation

Days offeredCredit hoursStart timeEnd time

BehaviorAdd a studentDelete a student

Get course rosterDetermine if it is full

Sample Class35



36


Decreasingabstraction

Increasingabstraction Asset

RealEstat

Savings

BankAccount

Checking Stock

Security

Bond

Elements at the same level of the hierarchy should be at the same

level of abstraction

Levels of abstraction36



37


Instance

An instance is an object created from a class

A class describes the behavior and information

structure of an instance, while the current stateof the instance is defined by the operationsperformed on the instance

System‘s behavior is performed via theinteractions between instances

37



38


multiple inheritance?

Person

name

NIC No

Student

std-id

level

Employee

emp-id

age

Inheritance

Specialization: The act of defining one class as a refinement ofanother (Generalized).

Subclass: A class defined in terms of a specialization of asuperclass using inheritance.

Superclass: A class serving as a base for inheritance in a class

hierarchy Inheritance: Automatic duplication of superclass attribute and

behavior definitions in subclass.

38



39


Why Inheritance?

Show similarities

Reuse common descriptions

‗Software Reuse‘

Easy modification of model by performingmodification in one place

Avoid redundancy, leading to smaller and

more efficient model, easier to understand

39



40


The ability to hide many differentimplementations behind a single interface

Manufacturer AManufacturer B

Manufacturer C

What is Polymorphism?40



41


Objects of different classes respond to the same

message differently.

Polymorphism

payTuition

Person

Name

NIC

Student

std-idlevel

Employee

emp-id

In-StateStudent

payTuition payTuition

Out-of-StateStudent

payTuition

41



42


Why Polymorphism

A very strong tool for allowing systemdesigners to develop flexible systems (e.g.shape)

Designer only need to specify what shall occurand not how it shall occur

To add an object, the modification will only

affect the new object, not those using it

42



43


Tube

Pyramid

Cube

Shape

DrawMoveScale

Rotate

<<interface>>

Realization relationship

What is an Interface?

Interfaces formalize polymorphism Interfaces support ―plug-and-play‖

architectures

43



44


• Information hiding - all data should be hidden within a class, at least inprinciple.

• make all data attributes private

• provide public methods to get and set the data values ( We don‘tnecessarily need to have getter setters for variables relevant internally only)

• e.g. Access to the grade information should be done through public

methods , such as setGrade and getGrade

payTuition

setGrade()

getGrade()

Studentstd-idLevelgrade

Interfaces (Public)44

Abstract Class vs Concrete



45


Abstract Class vs. ConcreteClass

Abstract Class.

Which can not be instantiated

Because it has at-least one abstract method

(method which has no implementation) Concrete class.

Is a complete class. (what is a complete class ?)

Describes a concept completely.

Is intended to be instantiated.

45



46


State of an Object

What is STATE ?State is defined by the current values of theattributes or properties

What is STATE CHANGE ? A "state change" is the transition of an objectfrom one state to another.

What is EVENT ?An "event" is a noteworthy change in state [Rumbaugh]

46

What is Object Oriented



47


What is Object-OrientedApplication?

Collection of discrete objects, interacting w. eachother Objects have property and behavior (causing state

transition) Interactions through message passing (eg func or method

calls) A sender object sends a request (message) to another

object (receiver) to invoke a method of the receiverobject‘s)

Fn

Data

O1

Fn

Data

O2

Fn

Data

O3m1 m2{m in Fn}

47



48


Is It Any Good?

A system which is designed and modelledusing an object-oriented technology is:

Easy to understand

Directly related to realityNatural partitioning of the problem

More flexible and resilient to change

Systems can be developed more rapidly and at alower cost

48



49


Limitations of SSADM

Treat data and function separately -function/dataoriented method

More difficult to maintain and re-configure

E.g Information hiding/data protection either global or local Modifications are unpredictable (because of no data

encapsulation)

Method require more abstraction - not too natural

Large semantic gap between external and internalview of a system

49



50


Some Qualities of OO

Easier maintenance. Objects may beunderstood as stand-alone entities.

Objects are potentially reusable components.

For some systems, there may be an obvious

mapping from real world entities to systemobjects

50



OBJECT ORIENTEDMETHODS

51



52


Object-Oriented Methods

A technique for system modeling (not designing)

A technique to manage complexity inherent inanalysis, design, and implementation

For the analysis and design of system Provide integrated view of hardware and

software*

Provide a methodology for systemdevelopment

52



53


OO Methods

Object Oriented Design (OOD) -Booch (1983), pioneeringbut not quite scalable

Object-Oriented System Analysis (OOSA) - Shlaer Shlaer& Mellor (1988), essentially information analysis based on

data analysis based on data modeling

Object-Oriented Analysis (OOA) -Coad & Yourdon (1991), amethod for developing OO system mode

Object Modeling Technique (OMT) - Rumbaugh et al.(1991), entity/relationship modeling with extension to modelclasses, inheritance and behavior

53



54


OO Methods OO Methods.. (2)

Hierarchical Object-Oriented (HOOD) - ESA(1989), architectural design for Ada code.

Jacobson Use Case - Jacobson et al.(1992),

requirement (1992), requirement modeling,analysis, and design; also known as OOSE.

Unified Modeling Language (UML) – Booch,

Rumbaugh, Jacobson , (1997/2000), a methodthat provides a united OO approach to systemdevelopment

54

OO Methods - Some



55


OO Methods - SomeAdvantages

Reduce semantic gap between domain (theactual) and model (the design)

Closer to reality e.g. classification of objects

close to how human understand surroundings Easier to understand and maintain

Easier to modify

55

FAST National University of Computer and Emerging Sciences Islamabad Pakistan



OOAD

Fall 2010

Islamabad, Pakistan

OBJECT ORIENTED

ANALYSIS ANDDESIGN



57


What is OOAD?

• understanding, finding and describing concepts in the problem domain.

Analysis

• understanding and defining software solution/objects that represent the analysis concepts and will eventually be implemented in code.

Design

• Analysis is object-oriented and design is object-oriented. A softwaredevelopment approach that emphasizes a logical solution based onobjects.

OOAD

Traceability!

Involves both a notation and a process : Methodology

57



58


What Is Analysis and Design?

Analysis emphasizes an investigation of the problem andrequirements, rather than a solution. "Analysis" is a broad term, best qualified, as in requirements

analysis (an investigation of the requirements) or object analysis(an investigation of the domain objects).

Design emphasizes a conceptual solution that fulfills therequirements, rather than its implementation. For example, a description of a database schema and software

objects.

Ultimately, designs can be implemented.

The term is best qualified, as an object design or databasedesign.

Analysis and Design have distinct activities (hence workproducts) but both can be performed iteratively.

58

What Is Object-Oriented Analysis and



59


What Is Object-Oriented Analysis andDesign?

During object-oriented analysis, there is an emphasis on findingand describing the objects—or concepts—in the problem domain. For example, in the case of the library information system, some ofthe concepts include Book, Library, members, and librarian etc.

During object-oriented design, there is an emphasis on definingsoftware objects and how they collaborate to fulfill therequirements. For example, in the library system, a Book softwareobject may have a title attribute and a getChapter method.

59



60


An Example60

Object Oriented Analysis and



61


Analysis

Investigation of the problem

Design

Logical Solution

Construction

Code

DomainConcepts,Objects

Book

TitleAuthor

Print

DesignClass

Public class Book{

Private String title;public void print ();

}

OOLanguage

Code

Object Oriented Analysis andDesign

61

Object-Oriented Analysis &



62


Object Oriented Analysis &Design

1.

Findingobjects

2.

Organizingobjects

3.

Describinghow objects

interacts

4.

Defining theoperationsof objects

5.

Definingobjects

internally

62

O O



63


Organising Objects

ClassificationPartitioning- Similar objects- inheritance: ‗is a‘

Interactions/relationships between objects

AssociationComposition - structure object from parts

Aggregation - Whole/Part relationship: ‗has a‘

63

How to do OOAD



64


How to do OOAD- notation vs. process

UML is a notation. So are English,

Arabic,…

Notation > How

Process > What and When (steps)

Wh U OO?



65


Requirements Analysis

Architectural Design

Detailed Design

Implementation

Release

Maintenance

Q u a l i t yA s s ur an c e

Software Lifecycle

Traceability!

Where to Use OO?65

E P i



66


Error Propagation

Traceability!

Artificial problem??

Accidental design

66

Specifications are important



67


Specifications are importanttoo!

67

Specifications are important too



68


Specifications are important too(2)!

68



69


69

OOP VS OOAD



70


OOP VS OOAD

Knowing an object-oriented language (suchas Java) is a necessary but insufficient firststep to create object systems

Knowing how to "think in objects" is alsocritical

OOAD, Emphasizes mastery of the fundamentals,such as how to assign responsibilities to objects,frequently used UML notation, and common

design pattern.

70

UML d OOAD



71


UML and OOAD

The UML is a standard diagramming notation

As useful as it is to learn notation, there are more criticalobject-oriented things to learn; specifically, how to think inobjects—how to design object-oriented systems

The UML is not OOA/D or a method, it is simply notation*

Yet, one needs a language for OOA/D and "softwareblueprints," both as a tool of thought and as a form of

communication with others

Explore how to apply the UML in the service of doing OOA/D

71






OOAD

Fall 2010

HOW TO DO OOAD ?

Hi t i l P ti



74


OO Prog. Languages(Smalltalk, C++)

just program!

OO Design(Booch)

design thenprogram

OO Analysis(Rumbaugh, Jacobson)

Process Perspective OO Technology

Analyze (use case) first,

then design,

then programWhere are we heading?

Historical Perspective74

OO De elopment Processes



75


OO Development Processes

FusionHewlett Packard

Recommended Process and Models

ObjectSpace best practices

Larman‘s experiences

…

The Rational Unified Process (RUP)Rational; Booch, Jacobson, and Rumbaugh

Some Popular OOAD Processes (for reference only)

75

One Good Way: Use (OO) Design



76


O e Good ay Use (OO) es gPatterns??

Reusable solutions to typical problems ―Each design pattern systematically names, explains, and

evaluates an important and recurring design in object-orientedsystems.‖ [Gamma]

Name

• — identifies a particular pattern, creating a vocabulary.

Problem

• — identifies context when pattern should be applied.

Solution• — an abstract description of a design problem along with a

template object design that solves the problem.

Consequences

• — results and trade-offs of applying the pattern.

76

Who’s Behind Object-Orientation w. Diff.



77


o s e d Object O e tat oConcerns?

Knowledge Representation (inA.I.)

•Psychological Validity

•Philosophical Validity

•Computational Validity

Databases •Emphasis in Persistent Data(and now ACID properties)

• RelationalDB

• Network DB

• Hierarchical DB

•OODB

ProgrammingLanguages •Emphasis in Efficiency

•Simula, SmallTalk, C++, Protel, Java

System/SoftwareEngineering

ERDSDM

CM

ADT

ERD: Entity Relationship

Diagram

SDM: Semantic Data Model

ADT: Abstract Data Type

CM: Conceptual Model

Where does Unified Modeling Language come into this?

77

A New Paradigm with Evolving Object



78


g g jOrientation

OOP: Object-Oriented Programming Simula (1967), Smalltalk (70‘s), C++ (mid 80‘s), Eiffel,

Ada95, Turing, …

OOD: Object-Oriented Design

Taxis (1976), Adaplex, …, Grady Booch (1980) OOA: Object-Oriented Requirements RML (1981), James Rumbaugh (late 80‘s)

OO-Databases (OODBs): 1980-90‘s

OLE/DCOM, VisualBasic, CORBA, Java: mid 90‘s .Net, C#, (eb/voice…/-)XML, J2EE: into 2000+ UML: mid 90‘s and still evolving

78

Applying patterns and assigning



79


pp y g p g gresponsibilities

How should responsibilities be allocated toclasses of objects?

How should objects interact?

What classes should do what? These are critical questions in the design of a

system.

Certain tried-and-true solutions to designproblems can be (and have been) expressed asbest-practice principles, heuristics, or patterns— named problem-solution formulas that codifyexemplary design principles.

79

Assigning Responsibilities



80


Assigning Responsibilities

A critical, fundamental ability in OOA/D is to skillfullyassign responsibilities to software components

Why? …….. Because …

it is one activity that must be performed— either whiledrawing a UML diagram or programming

it strongly influences the robustness, maintainability, andreusability of software components

Nine fundamental principles in object design andresponsibility assignment

Organized in a learning aid called the GRASP patterns.

80

Some Design Principles to



81


g pconsider

Low Coupling

low dependency between classes;

low impact in a class of changes in other

classes; high reuse potential;

High Cohesion

focused, manageable and understandable.High cohesion means that the responsibilitiesof a given element are strongly related andhighly focused.

81

Quiz No 2



Quiz No 2

Explain Inheritance andPolymorphism. How bothare related with each other.*

82

Documents

02-Introduction to OOAD