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Entity Relationship Diagram as a technical tool also has predefined set of symbols. The purpose behind all
this is to have standardization in the use of technique in varied situations. Some major symbols
commonly used are as under.

Primary key attributes are
Dashed ellipses represent derived

Double ellipses represents multivalued

Lines link attributes to entity sets,
entity sets to relationship sets (also
represent roles)

Relationship (between two entities)

Attributes (of an entity)

Entity (a real world object)

ERD Example
The diagram shows a primary relationship is between two entities, employee and the department. The
relationship is of an employee working in a department. The figure also shows information available for
each of these entities.

Object Oriented Analysis and Design (OOAD)
The concept of object oriented analysis and design focuses on problems in terms of classes and objects.
This concept combines aspects of both entity relationship diagram and data flow diagrams. The object
oriented analysis and design tool has been devised to support the object oriented languages, for example
C++ and Java. The roots of the concept of object orientation evolved in late 60’s with the emergence of
first language “SIMULA 67” as the first object oriented language. Object oriented methodologies do not
replace traditional approaches (such as data flow, process flow, and state transition diagrams); they are
important new additions to the toolkit.

26.1 Why need Object-Orientation?
There are certain positive points which are becoming stronger reasons for the increased use of this
Object orientation helps in increasing abstraction and event-driven programming
The widespread use of Graphical User Interface (GUI) encourages use of object orientation.
Software can be developed on modular basis
1. Easier to maintain
2. Easier to upgrade
3. Easier to test
4. Easier to develop incrementally
Reusable Software – The software developed using object oriented approach can be easily reused
due to independence/uniqueness of the objects i.e. an independent accounting module built in
object oriented environment can be made a part of a complete ERP solution without developing it
again from scratch for ERP.

26.2 Object Oriented Analysis
Name Dept. ID Dept. Name
Employees Works In Departments
Emp. ID
College Degree
Hire Date
No. of employees

The concept of analysis has been defined from different perspectives in different approaches to system
"The development activity consisting of the discovery, modeling, specification and evaluation of
Donald Firesmith (Dictionary of Object Technology, 1995),

In OOAD analysis has been defined in a different manner
"The discovery, analysis and specification of requirements in terms of objects with identity that encapsulate
properties and operations, message passing, classes, inheritance, polymorphism and dynamic binding.”
Object oriented Design
The concept of design has been defined from different perspectives in different approaches to system
“Systems design is the process or art of defining the hardware and software architecture, components,
modules, interfaces, and data for a computer system to satisfy specified requirements.”
In OOAD analysis has been defined in a different manner. According to Firesmith
“The design of an application in terms of objects, classes, clusters, frameworks and their interactions is
called OOAD Analysis."

Basic Concepts
Following are the basic concepts related to this technique.

An object is defined as
“an abstraction of something in a problem domain, reflecting the capabilities of the system to keep
information about it, interact with it, or both.”
Coad and Yourdon (1990)
An object is any abstraction that models a single concept.

Another Definition of object
“A concept, abstraction, or thing with crisp boundaries and meaning of the problem at hand. Objects serve
two purposes. They promote understanding of the real world and provide a practical basis for computer
Rumbaugh et al. (1991)

Components of object
According to Booch, there are three components of object. Objects have state, behavior and identity.
Identity: Who is it?
Each object has unique identity.
Behavior: What can it do?
What an object can do, how it can respond to events and stimuli.
State: What does it know?
The condition of an object at any moment, affecting how it can behave
Real-world objects share two characteristics: They all have state and behavior.
For example,
Dogs have state (name, color, breed, hungry) and behavior (barking, fetching, wagging tail).
Bicycles have state (current gear, current pedal cadence, two wheels, number of gears) and behavior
(braking, accelerating, slowing down, changing gears).


Software objects are modeled after real-world objects in that they too have state and behavior. We might
want to represent real-world dogs as software objects in an animation program or a real-world bicycle as
software object in the program that controls an electronic exercise bike.

A class is defined as
“The purpose of a class is to specify a classification of objects and to specify the features that characterize
the structure and behavior of those objects.”
A class is any uniquely identified abstraction, that is, model of a set of logically related objects that share the
same or similar characteristics. The purpose of a class is to specify a classification of objects and to specify
the features that characterize the structure and behavior of those objects.
An object is an instance of some class. All objects are instances of some class. Instance also carries
connotations of the class to which the object belongs.
For example, computers are the domain/Class which can be divided into following sub-classes:
Laptop computer
Desktop computer
In the sub-sub-class of laptops, we may identify various laptop models or brands which may then have a
further division on a model-wise basis.

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