# Explain degree of relationship and cardinality of relationship

## Introduction

The degree of a relationship is the number of entities participating in that relationship. The cardinality of a relationship is the number of times an entity can participate in that relationship. In other words, the degree of a relationship is the number of “ends” that the relationship has, while the cardinality of a relationship is the number of “times” an entity can appear at each end.

## What is the degree of the relationship?

In database design, the degree of relationship is the number of entity types that are associated with each other in a relationship. The cardinality of a relationship is the number of occurrences of one entity type that can be associated with each occurrence of another entity type.

There are three degrees of relationships:

One-to-one: In a one-to-one relationship, each occurrence of entity A can be associated with only one occurrence of entity B, and each occurrence of entity B can be associated with only one occurrence of entity A.

One-to-many: In a one-to-many relationship, each occurrence of entity A can be associated with multiple occurrences of entity B, but each occurrence of entity B can be associated with only one occurrence of entity A.

Many-to-many: In a many-to-many relationship, each occurrence of entity A can be associated with multiple occurrences of entity B, and each occurrence of entity B can be associated with multiple occurrences ofentityA.

## What is the cardinality of relationship?

The cardinality of a relationship indicates the number of objects that can be associated with each other. For example, in a one-to-one relationship, each object is associated with only one other object. In a one-to-many relationship, each object is associated with multiple other objects. Finally, in a many-to-many relationship, each object is associated with multiple other objects and vice versa.

## How are the degree and cardinality of relationship related?

The degree of a relationship is the number of participating entities in that relationship. The cardinality of a relationship is the number of times an entity can participate in that relationship. The two are related in that the cardinality of a relationship determines the maximum degree of that relationship. For example, a “one-to-many” relationship has a maximum degree of two (one “one” entity and many “many” entities), while a “many-to-many” relationship has a maximum degree of four (many “one” and “many” entities).

## Examples of degree and cardinality of relationship

Degree refers to the number of participating entity types in a relationship. For example, a one-to-one (1:1) relationship has two participating entity types, a one-to-many (1:N) relationship has two participating entity types, and a many-to-many (M:N) relationship has three participating entity types. Cardinality refers to the number of occurrences of one entity type that are related to one occurrence of another entity type. For example, in a one-to-one (1:1) relationship, there is one occurrence of each entity type that is related to each other. In a one-to-many (1:N) relationship, there is one occurrence of the first entity type that is related to many occurrences of the second entity type. In a many-to-many (M:N) relationship, there are many occurrences of both entity types that are related to each other.

## Conclusion

The degree of a relationship is the number of entity types that participate in the relationship. The cardinality of a relationship is the number of occurrences of one entity type that are related to one occurrence of the other entity type. The degree and cardinality of a relationship can each be expressed as either a minimum or a maximum value.