Illustrate this concept with an example

Let us suppose that we have an employee table. A manager supervises a subordinate. Every employee can have a supervisor except the CEO and there can be at most one boss for each employee. One employee may be the boss of more than one employee. Let’s suppose that REPORTS_TO is a recursive relationship on the Employee entity type where each Employee plays two roles

1. Supervisor
2. Subordinate

3. Supervisor and Subordinate are called “Role Names”. Here the degree of the REPORTS_TO relationship is 1 i.e. a unary relationship.

   • The minimum cardinality of Supervisor entity is ZERO since the lowest level employee may not be a manager for anyone.
   • The maximum cardinality of Supervisor entity is N since an employee can manage many employees.
   • Similarly the Subordinate entity has a minimum cardinality of ZERO to account for the case where CEO can never be a subordinate.
   • It maximum cardinality is ONE since a subordinate employee can have at most one supervisor.

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