Question

Help with this assignment for database systems course :

Draw the entities and relationships suggested by each word problem.  Include the proper foreign key(s). Remember to make a copy for yourself.  

Unary Relationships

3- Employees (Empid, name) can mentor other employees, or not.  Every employee has a single mentor. Mentors only have one person that they mentor at a time (a mentee).  When they get a new mentee we just overwrite the record of the previous mentee.

4- Same as #3 but we do want to keep the historical record of all mentor / mentee relationships, as well as the start and end date of each.

Answer 1

3.

Employee to Employee_mentor is One-to-One relationship
Employee_mentor table has the Mentor as the foreign key referred from Empid of employee table and also Mentee is a FK referred from Empid of Employee table

4.

We can just maintain a single table where MentoredBy is the foreign key referred from other Empid
If employee is the Mentor then MentoredBy is NULL