Cardinality Ratio in DBMS

Cardinality Ratio in DBMS

 

In this article, we will learn about the Cardinality Ratio in DBMS.

  • Cardinality tells how many times the entity of an entity set participates in a relationship
  • There are 4 types of cardinalities
    • One to one
    • One to many
    • Many to one
    • Many to many
Cardinality Ratio in DBMS

1. One to one cardinality

  • When a single instance of an entity is associated with a single instance of another entity, then it is called as one to one cardinality
  • Here each entity of the entity set participate only once in the relationship.
Example for one to one cardinality :

Assume that the only male can be married to only one female and one female can be married to only one male, this  can be viewed as one to one  cardinality

One to One Relationship Cardinality in DBMS

2. One-to-Many  cardinality

  • When is a single instance of an entity is associated with more than one instance of another entity then this type of relationship is called one to many relationships
  • Here entities in one entity set can take participation in  any number of times in relationships set and entities in another entity set can take participation only once in a relationship set.
Example for one to many cardinalities

 For example in the Real world, many students can study in a single college but the student cannot apply to more than one college at the same time

One to Many Relationship Cardinality in DBMS

3. Many-to-one cardinality

When entities in one entity set can participate only once in a relationship set and entities in another entity can participate more than once in the relationship set,  then such type of cardinality is called many-to-one

Example for many to one cardinality
    • In real time a student takes only one course but a single course can be taken by any number of students. so many to  one relationship is observed here
    • It means that one course can be taken by any number of students but only one course can be allotted to one student 
Many to One Relationship Cardinality in DBMS

4. Many-to-many cardinality

  • Here  more than one instance of an entity is associated with more than one instance of another entity then it is called many to many relationships
  • In this cardinality, entities in all entity sets can take participate any number of times in the relationship cardinality is many to many.
Example for many to many cardinality
    • In the Real world assume that a student can take more than one course and the single course can be taken by any number of students this  relationship will be many to many relationship
Many to Many Cardinality in DBMS
Learn more about DBMS here on this page.