dbms conceptual modeling, Lecture notes of Database Management Systems (DBMS)

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Conceptual Modelling

using ER model- Day 1

CS105:DATABASE MANAGE ME NT SYSTE MS

ISURA NIRMAL |ISURA.N@ NSBM.LK| SCHOOL OF COMPUTING

Entity Relationship Model

Entity Relationship(ER) Model is a conceptual data model which can

be used in designing a database.

The three main constructs of the ER model are,

◦ Entities ◦ Attributes ◦ Relationships

ER Model is an Illustration. So we need a Modelling Notation

◦ Standard Symbols to use ◦ Chen Notation

What is a “Entity”?

An entity can be a real-world object, either animate or inanimate,

that can be easily identifiable.

As an example, in a school database, students, teachers, classes, and

courses offered can be considered as entities.

First letter of each word in the entity name is uppercase

E.g., Student, Teacher, Class, Course

Normally an entity is named using a “ noun ‟ or “ noun phrase ‟

What are the entities in Library?

Types of Entities

Strong (Regular) Entity

◦ An entity that exists independently of other entity types

Weak Entity

◦ An entity types whose existence depends on some other entity ◦ This is depended on the scenario (interaction with other entities) ◦ I.e :- A call cannot exist without phone (phone number)

Represented by using a rectangle

Types of Attributes

Simple attribute / Single-value attribute An attribute that cannot be broken down into smaller components Composite attribute An attribute that can be broken down into component parts Derived attribute An attribute whose values can be calculated from related attribute values

Types of Attributes

Multi-value attribute An attribute that may take on more than one value for a given entity instance (I.e ;_ phone number) Key Attribute Uniquely identifiers individual instances of an entity type Can be single attribute or combination of attributes that uniquely identifies individual instances of an entity type

Some Examples

Some Examples