Cardinality Ratio in DBMS
Cardinality Ratio in DBMS
On this page, we will learn about the Cardinality Ratio in DBMS.
Cardinalitytells how many times the entity of an entity set participates in a relationship- There are 4 types of cardinalities
One to oneOne to manyMany to oneMany to many
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 a one to one cardinality
- Here each entity of the entity set participates 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
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
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
It means that one course can be taken by any number of students but only one course can be allotted to one student
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
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