I request the assistance I work on the library database, But I have problem on the erd and relationship between entity ,if any one can help me I am grateful to him .
this my project if any one can add some entity and the erd please:
The system contains entities that act and participate with the system , these entities are :

Employee Entity : each employee has an ID, Name, DOB , Address , telephone # , and supervised by other employee. The employee deal with supplier who supply the books, and treat each order comes from customer

Book Entity : each book has an ID , Name , Author Name , Book Category , and Price of the book.

Customer Entity : each customer has an ID, Name, Address , Telephone # , the customer is person who borrowing books from the library .

Supplier Entity : each supplier has an ID , Name , Telephone # , Address , the supplier is supply the library with different category of books.

Order Entity : each order has an ID , order date , delivery date , ID for the employee , and the ID for the customer who borrowed the books , Quantity of the order .