The number of entities to which another entity can be associated via a relationship set is expressed as :

The number of entities to which another entity can be associated via a relationship set is expressed as the cardinality of the relationship. In relational database theory, cardinality defines the number of occurrences of one entity in relation to the number of occurrences of another entity.

There are several types of cardinality:

1. One-to-One (1:1): Each entity in set A is related to one and only one entity in set B and vice versa.
2. One-to-Many (1:M): Each entity in set A can be associated with multiple entities in set B, but each entity in set B is associated with only one entity in set A.
3. Many-to-One (M:1): Multiple entities in set A can be associated with one entity in set B, while that entity in set B can be related to only one in set A.
4. Many-to-Many (M:N): Entities in set A can be associated with multiple entities in set B and vice versa.

Understanding cardinality is vital for database design and ensuring data integrity through meaningful relationships between different kinds of entities.