ER Model in DBMS

PRESENTATION
ER-DATA MODEL
IN
DBMS
PRESENTATION BY:
-KABINDRA KOIRALA

OBJECTIVES
● Entity Relationship Model
● Entity Relationship Diagram(ERD)
● Extended Features of ERD

1.ENTITY RELATIONSHIP MODEL
● ER Model- Basic Concepts
● Entity
● Attributes and its types
● Entity-set and keys
● Relationship And Mapping Cardinality

ER Model - Basic Concepts
The ER model defines the three most relevant
steps. It works around real-world entities and
the associations among them. At view level, the
ER model is considered a good option for
designing databases.
● Requirement Analysis
● Conceptual Database Design
● Logical Database Design

Requirement Analysis
The very first step in designing a database
application is to understand what data us to be
stored in the database, what applications must
be built on the top of it, and what operations are
we must find out what the users want from the
database.

Conceptual Database Design
The information gathered in the requirements
analysis step is used to develop a high-level
description of the data to be stored in database,
along with the constraints known to hold over
the data.
The ER model is one of the high-level or
semantic, data models used in database.

Logical Database Design
We must choose a DBMS to implement our
database design, and convert the conceptual
database design into a database schema in the
data model of chosen DBMS. Sometimes
conceptual schema is called logical schema in
Relational Data Model.

Entity
● An entity can be a real-world object, either animate or
inanimate, that can be easily identifiable. For example, in a
school database, students, teachers, classes, and courses
offered can be considered as entities. All these entities have
some attributes or properties that give them their identity.
● An entity set is a collection of similar types of entities. An
entity set may contain entities with attribute sharing similar
values. For example, a Students set may contain all the
students of a school; likewise a Teachers set may contain all
the teachers of a school from all faculties. Entity sets need
not be disjoint.

Attributes
● Entities are represented by means of their properties, called
attributes. All attributes have values. For example, a student
entity may have name, class, and age as attributes.
● There exists a domain or range of values that can be assigned
to attributes. For example, a student's name cannot be a
numeric value. It has to be alphabetic. A student's age cannot
be negative, etc.

Types of Attributes
●
Simple attribute − Simple attributes are atomic values, which cannot be divided further. For
example, a student's phone number is an atomic value of 10 digits.
●
Composite attribute − Composite attributes are made of more than one simple attribute. For
example, a student's complete name may have first_name and last_name.
●
Derived attribute − Derived attributes are the attributes that do not exist in the physical
database, but their values are derived from other attributes present in the database. For
example, average_salary in a department should not be saved directly in the database, instead it
can be derived. For another example, age can be derived from data_of_birth.
●
Single-value attribute − Single-value attributes contain single value. For example −
Social_Security_Number.
●
Multivalued attribute − Multivalued attributes may contain more than one values. For example,
a person can have more than one phone number, email_address, etc.

Entity-Set and Keys
Key is an attribute or collection of attributes that uniquely identifies an entity
among entity set. For example, the roll_number of a student makes him/her
identifiable among students.
There are mainly three types of keys:
● Super Key − A set of attributes (one or more) that collectively identifies an
entity in an entity set.
● Candidate Key − A minimal super key is called a candidate key. An entity set
may have more than one candidate key.
● Primary Key − A primary key is one of the candidate keys chosen by the
database designer to uniquely identify the entity set.

Relationship
The association among entities is called a relationship. For example, an employee works_at a
department, a student enrolls in a course. Here, Works_at and Enrolls are called relationships.
● Relationship Set: A set of relationships of similar type is called a relationship set. Like entities, a
relationship too can have attributes. These attributes are called descriptive attributes.
● Degree of Relationship:The number of participating entities in a relationship defines the degree of
the relationship.
Binary = degree 2
Ternary = degree 3
n-ary = degree

Mapping Cardinalities
Cardinality defines the number of entities in one
entity set, which can be associated with the
number of entities of other set via relationship
set.

Types of Cardinalities
1.One-to-one
One entity from entity set A can be
associated with at most one entity
of entity set B and vice versa.
2.One-to-many
One entity from entity set A can be associated with more
than one entities of entity set B however an entity from
entity set B, can be associated with at most one entity

Types of Cardinalities(cont…..)
● Many to One
More than one entities from entity set A can
be associated with at most one entity of
entity set B, however an entity from entity
set B can be associated with more than one
entity from entity set A.
● Many to Many
One entity from A can be associated
with more than one entity from B
and vice versa.

2.ENTITY RELATIONSHIP DIAGRAM
● Introduction
● Symbols & Notations
● Information Engineering Style Used in ER-
Diagram

Introduction
ER-Diagram is a visual
representation of data
that describes how
data is related to each
other.

SYMBOLS AND NOTATIONS
● Entities: An entity is an object or
concept about which you want to store information.
A weak entity is an entity that must
defined by a foreign key relationship with
another entity as it cannot be uniquely identified by its
own attributes alone.

SYMBOLS AND NOTATIONS(cont….)
● Actions: Actions are represented by
diamond shape, and show how two,
entities share information in the database.
In some cases, entities can be
Self-linked.
For example,employees can supervise other employees

● Attributes: Attributes are represented
by ovals. A key attribute is the unique, distinguishing
characteristic of the entity.
For example, an employee's social security number might be the employee's key attribute.
A multivalued attribute can have more than one value.
For example, an employee entity can have multiple skill values.
A derived attribute is based on another attribute.
For example, an employee's monthly salary is based on the
employee's annual salary. ATTRIBUTE
ATTRIBUTE
ATTRIBUTE

● Connecting lines: Solid lines that connect attributes to
show the relationships of entities in the diagram.
● Cardinality: Cardinality specifies how many instances
of an entity relate to one instance of another entity.
Ordinality is also closely linked to cardinality. While
cardinality specifies the occurrences of a relationship,
ordinality describes the relationship as either
mandatory or optional. In other words, cardinality
specifies the maximum number of relationships and
ordinality specifies the absolute minimum number of
relationships.

INFORMATION ENGINEERING STYLE
USED IN ER- DIAGRAM
MEANING
● Zero or More
● One or More
● One and only One
● Zero or One
Relationships (Cardinality and Modality)
SYMBOLS
●
●
●
●

USED IN ER- DIAGRAM(cont...)
MEANING
● A one through many notation on one
side of a relationship and a one and
only one on the other.
● A zero through many notation on one
side of a relationship and a one and
only one on the other.
● A one through many notation on one
side of a relationship and a zero or one
notation on the other.
● A zero through many notation on one
side of a relationship and a zero or one
notation on the other.
Many - to - One
SYMBOLS
●
●
●
●

USED IN ER- DIAGRAM(cont...)
MEANING
● A zero through many on both sides of a
relationship.
● A one through many on both sides of a
relationship.
● A zero through many on one side and a
one through many on the other.
● A one and only one notation on one side
of a relationship and a zero or one on
the other.
● A one and only one notation on both
sides
Many - to - One
SYMBOLS
●
●
●
●
.

3.EXTENDED FEATURES OF ERD
● Introduction
● Generalization
● Specialization
● Inheritance

Introduction
The ER Model has the power of expressing database entities in a conceptual
hierarchical manner. As the hierarchy goes up, it generalizes the view of entities, and
as we go deep in the hierarchy, it gives us the detail of every entity included.
Going up in this structure is called generalization, where entities are clubbed together
to represent a more generalized view. For example, a particular student named
Kabindra can be generalized along with all the students. The entity shall be a student,
and further, the student is a person. The reverse is called specialization where a
person is a student, and that student is Kabindra.

Generalization
In generalization, a number of
entities are brought together into
one generalized entity based on
their similar characteristics. For
example: Kabindra, Mukesh, Gopal,
Shiv Chandra can all be generalized
as member of this Group.
Members of this group
Kabindra
Mukesh Gopal
ShivChandra

Specialization
Specialization is the opposite of generalization. In
specialization, a group of entities is divided into sub-
groups based on their characteristics. Take a group
‘Person’ for example. A person has name, date of
birth, gender, etc. These properties are common in all
persons, human beings. But in a company, persons
can be identified as employee, employer, customer, or
vendor, based on what role they play in the company.
PERSON
TEACHERSTUDENT
IS A

Inheritance
We use all the above features of ER-Model in order to
create classes of objects in object-oriented programming.
The details of entities are generally hidden from the user;
this process known as abstraction.
Inheritance is an important feature of Generalization and
Specialization. It allows lower-level entities to inherit the
attributes of higher-level entities.
For example, the attributes of a Person class such as
name, age, and gender can be inherited by lower-level
entities such as Student or Teacher.
PERSON
TEACHERSTUDENT
IS A
GENDER
AGE
NAME
ROLL NO. ID NO.

Conclusion
So, in this presentation, we studied about Data
Models and its parts, i.e Entity Relationship
Models, Entity Relationship Diagram and its
Extended Features. Beside this, we also learn
about the use of them in database system the
application, which the information technology
field use as one of the major software in
computer field.

ER Model in DBMS

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