Databases Reference
In-Depth Information
Figure 15.3
ER diagram for a simple database.
•
Each customer may place many orders, but only one customer may place a par-
ticular order.
•
Each department has many salespeople, but each salesperson must work in only
one department. (Note: This may not be a realistic constraint for some retail
businesses.)
•
Each department has many items for sale, but each item is sold in only one
department (item means item type, like IBM PC).
•
For each order, items ordered in different departments must involve different
salespeople, but all items ordered within one department must be handled by
exactly one salesperson. In other words, for each order, each item has exactly one
salesperson, and for each order, each department has exactly one salesperson.
