In mathematics, the term cardinality of a set is a measure of the “number of elements” present in the set. For example, let us consider one set with four elements A = { 2,5,7,9 }.

The set** A ** contains **4 **elements, and therefore set A has a cardinality of four. Cardinality = 4.

For example , if the student table contains hundred unique records of the students than the cardinality will 100.

In DBMS , A relation or an entity is represented by a table in a relational model. The entity set contains the number of unique instances present in a set. The number of such unique instances present in a set is referred as cardinality.

The cardinality of relationship in DBMS is defined as the number of instances of one entity set that can be associated with the number of instances present in another entity set in a given relationship.