Object-Oriented Software Design: Lecture Notes on Basic Mechanisms and Key Concepts - Prof, Lecture notes of Software Engineering

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Object-Oriented

Software Design (lecture 7)

Basic Mechanisms:

Objects:

 A real-world entity.

 A system is designed as a set of

interacting objects.



Consists of data (attributes) and

functions (methods) that operate on data

 Hides organization of internal information

(Data abstraction)

 Examples: an employee, a book etc.

 Class:

Instances are objects

Template for object creation

Examples: set of all employees,

different types of book

 Methods and message:

 Operations supported by an

object

 Means for manipulating the data

of other objects

 Invoked by sending message

 Examples: calculate_salary, issue-

book, member_details, etc.

 Multiple Inheritance:

Subclass can inherit attributes and

methods from more than one base

class

Multiple inheritance is represented

by arrows drawn from the subclass to

each of the base classes

LibraryMember

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Base Class

Derived

Classes

LibraryMember

UnderGrad PostGrad Research

Faculty Students Staff

Base Class

Multiple

Inheritance

 Advantages of abstraction:

Reduces complexity of software

Increases software productivity



It is shown that software

productivity is inversely

proportional to software

complexity

 Encapsulation:

Objects communicate outside world

through messages

Objects data encapsulated within its

methods

 Polymorphism:

 Denotes to poly (many)

morphism (forms)

 Same message result in

different actions by different

objects (static binding)

 Dynamic binding:

In inheritance hierarchy, an object can be

assigned to another object of its ancestor

class

A method call to an ancestor object would

result in the invocation of appropriate

method of object of the derived class

 Composite objects:

Object containing other objects

 Code and design reuse

 Increased productivity

 Ease of testing & maintenance

 Better understandability

 Its agreed that increased

productivity is chief advantage

Advantages

of Object-oriented design

 UML is a modelling language

 Not a system design or

development methodology

 Used to document object-

oriented analysis and design

 Independent of any specific

design methodology

Object

modelling using UML

 Based Principally on

 OMT [Rumbaugh 1991]

 Booch’s methodology[Booch 1991]

 OOSE [Jacobson 1992]

 Odell’s methodology[Odell 1992]

 Shlaer and Mellor [Shlaer 1992]

UML