What is ER Model?

ER model stands for a Entity Relationship Model it is a high-level data model. This model is used to define the data elements and rlationship fo a specified system. It develops very simple and easy to view of data to understand conceptual database design. It also called "entity relationship digram".

ER Model

ER Digram is a collection presenting Entites, Attributes and Relation. That have presented by different sybmols.

Entity

Entity is the simple mean collection of Attribute (column) and tuple (row) that you are called Table. Only two type entity present Strong and Weak

Strong Entity it called also as primary entity or master table. Those entity inside present primary attribute they are strong eneity. Prsent by single border.
Strong Entity
Weak Entity it called also as secondary entity or slave table. Those entity inside not present primary attribute they are strong eneity. Present by double border.
Weak Entity
Attribute

Attribute that you are know the name of (column).

Simple Attribute is normal present a column like CLASS.

class

Key Attribute is present primary column that make entity primary entity like id number of school.

student_id

Multivalued Attribute is present column those have multiple value set like CONTACT number possiblity to mutliple number of a person.

contact_number

Composite Attribute is present those column would split into mulitple column like NAME divide into first_name, last_name, middle_name and ADDRESS divide into country, city, address. Column split into multiple column

name
|
| | |
first_name
middle_name
last_name

Drived Attribute is present those column that value calculate by other value example like AGE calculate by DOB and PERCENTAGE calculate by mark. Column specified by dotted border.

age
−−−−−
date_of_birth
Relation

Relation is very important part of the digram that presenet relationship (roll) between entities. It relation topic is make Relational Database Mangement System. Four type relation present in ER Model.

One To One that case only one attribute relationship to secondary table single attribute.
−
One To Many that case only one attribute relationship to secondary table mutiple attribute.
→
Many To One that case multiple attribute relationship to secondary table single attribute.
←
Many To Many that case multiple attribute relationship to secondary table multiple attribute.
↔
Example
er