Relationships between data objects within the same entity.
The most common type of relationship in data modeling is the one between entities. Recursive relationships are those that exist within an entity and do not require another entity to establish the link between records. A frequently found example is that of employees and managers within an employee database. All managers are employees and most employees have a manager. In order to find an employee's manager, it is necessary to identify the manager's employee id and locate them in the employee database.