1. Practice of ER modeling
Yong Choi
School of Business
CSUB

2. Identify Cardinality
A purchase order may be for many products. A product may appear on many purchase orders.
A customer may submit many orders. An order is for exactly one customer.

3. Eliminate unnecessary details and refine Business Rule 1
According to the policy of the California Hospital, a patient can have patient records. That is, each patient may have at least one or many records. However, each patient record should be belonged to one patient.

4. Eliminate unnecessary details and refine Business Rule 2
The California State University has changed one of the policies about course schedule based upon feedback from professors and students. One of the changed policies is that a course may have one or more scheduled sections. Also, each section can have one course. Creating correct number of sections for each semester is very important. So, the registration office is required to communicate with each department chair during summer break.

5. Multiple Entities 1
CSUB is the only 4 years comprehensive university in Kern County. Each class offered by CSUB may be taught by several professors. A particular class may always uses the same room. Because classes may held at different times or on different evenings, it is possible that each room is used by many different classes. By the way, A professor can teach several classes.

6. Multiple Entities 2
A salesperson may manage many other salespeople. A salesperson is managed by only one salesperson. A salesperson can be an agent for many customers. A customer is managed by one salesperson. A customer can place many orders. An order can be placed by one customer. An order lists many inventory items. An inventory item may be listed on many orders.

7. Multiple Entities 2 con’t
An inventory item is assembled from many parts. A part may be assembled into many inventory items. Many employees assemble an inventory item from many parts. A supplier supplies many parts. A part may be supplied by many suppliers.

8. Multiple Entities and Attributes
Recently, our company installed a new relation database system and the company database needs to store information about employees, departments and children of employees. Each employee can be identified by ssn with salary and office phone number. Likewise, each departments also can identified by dno with dname and budget. Especially, children of employees should be identified with last name and age.

9. Multiple Entities and Attributes (con’t)
Employees work in departments; each department is managed by an employee; a child must be identified uniquely by name when the parent (who is an employee; assume that only one parent works for the company) is known. We are not interested in information about a child once the parent leaves the company.