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.