Introduction to ER Diagrams

Introduction

Entity Relationship Diagram which simply known as ER-Diagram or ERD describes the structure of the DB diagramatically. It works as the Road Map for the Database which we are going to implement later.

1. Entity Sets / Entities
2. Attributes
3. Relationship Sets / Relationships

Geometric Shapes for ER-Diagram    

Weak Entity

Weak Entity is an entity which can't be uniquely identified a given record by only using it's own attributes alone as this entity is completely(Totally) depend on the other Relationship. So, to keep the uniqueness of each record of data we need to use a foreign key(Primary Key of other Entity) in conjunction with its attributes to create a primary key.

Entity Relationships

Entity relationships can be categorised into four types. They are;

                1. One to One Relationship - (1 : 1)

                2. One to Many Relationship - (1 : M)

                3. Many to One Relationship - (M : 1)

                4. Many to Many Relationship - (M : M)

✱important:- (1 : 1), (1 : M), (M : 1), (M : M) are the Cardinality Ratio for those relationships

One to One Relationship - (1 : 1)

❄️ In this One to One Relationship Student is the Inverse (Main     Charactor) and Wach is the Outverse (Object Charactor).

One to Many Relationship (1 : M)

Many to One Relationship - (M : 1)

Many to Many Relationship - (M : M)

Unary Relationship

In a Unary Relationship, both of the participants are same Entity. 

Binary Relationship

In a Binary Relationship, two different participants are involved.

Ternary Relationship

In a Ternary Relationship, three different participants are involved.

N - ARY Relationship

When a large No of entity sets are participating in a relation, it is called as a N-ARY Relationship.
In here N represents the no of Entities which involves in the given relation. The above mentioned Unary Relationship, Binary Relationship, Ternary Relationship are special moments of N-ARY Relationship.

1. Unary Relationship - (Only One Entity involves the Relation)
2. Binary Relationship - (Only Two Entity involves the Relation)
3. Ternary Relationship - (Only Three Entity involves the Relation)

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