Chapter 12 What is ERD and Types Explain in Details

CHAPTER 12

ERD

(ENTITY RELATIONSHIP DIAGRAM ) 

ER-Model :- ER- Model Stand for entity relationship model.

It is a graphical approach for designing a database, It’s database modelling technique that generated an abstract diagram of system data and that diagram is used in designing a relational database. It was developed by Peter Chen in 1976.

ERD:- ERD stands for Entity Relationship Diagram, The Diagram generated by ER-Model is known as ERD. ERD show the relationship of different entities stored in the database.

Customer

Name	Address
Shailesh	India / 23333
Chu So Shang	South Korea/ 33322

 

 

Product/ Item

Name	Price
Mouse	250/-
Keyword	750/-

 

ER Diagram explains the logical structure of database, at last an ERD is implemented as a database. It helps us to analyze data requirements systematically to produce a well design database. It is considered as a best practice to completed ER Modelling before implementing your database.

ER diagram are based on three basic concepts entities, attributes and relationship.

1.)    Entity :-An Entity is a real world object or concept about which your want to store information, An Entity can be place, person, object, or a concept etc. (as a Noun )

a.)    Persons :- Students, Employees, Patient..

b.)   Place :- Building, store..

c.)    Object :- Car, Bike, Product..

d.)   Concept :- Course (BCA, BBA, B-Tech, MBA..)

2.)    Attributes :- An attributes are the properties or characters of an entity, It describes an entity, it is represented using oval shape.

3.)    Relationship :- It specifies how entities are associated with each other. It is represented using diamond shape.

Important and uses of ERD:-

Database Design

Database debugging

Problem in requirement gathering

 

Entity Types :-

1.)    Strong Entity :- An Entity which does not depends on any other entity to exits is called Strong entity .

Ex:- Employees

2.)    Weak Entity :- An Entity Which depends on other entity to exist is called weak entity.

Ex :- Loan

Attribute Types :-  

a.)    Single value attributes

b.)   Multi-value attributes

c.)    Simple attributes

d.)   Composite attributes

e.)    Derived attributes

f.)     Key attributes