This database seems to be an order/stock management system. A Customer (Customers table), with a unique CustomerID as a Primary Key, places an order that is identified with a unique OrderID which is the primary key of the Orders table and CustomerID as a foreign key. One customer can have many orders but a order can only have one customer. The Orders table is linked to the Order Details table which is a linking table between Orders and Products as it has both ProductID and OrderID as foreign keys but not primary key of its own. The Employees table identifies the employee of the company that placed the order. The employ is included in the Orders table via the foreign key EmployeeID, which is the primary key of the Employees table. An employee can have many orders, but an order can have only one employee associated with it. Lastly, the Shippers table is used to identify the Shipping company responsible for the order delivery. It has a primary key of ShipperID .