Practice of ER modeling Yong Choi School of Business CSUB

Practice 1 A department hires many employees. A employee is hired by one department. A manager manages one department. A department is managed by one manager.

Practice 2 An author writes many books. A book is written by many authors. A team consists of many players. A player plays for only one team.

Practice 3 A purchase order may be for many products. A product may appear on many purchase orders. Purchase Order (many, optional) Product (many, optional) A customer may submit many orders. An order is for exactly one customer. Customer (one) Order (many, optional)

Practice 4 Eliminate unnecessary information and refine The California State University has changed one of the policies about the 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, or may not have a scheduled section. Each section has one course or may not have any course at all.

Practice 5 – Multiple Entities There are several departments in each school at CSUB. Each department belongs to one school. A department has many professors, but a professor may belong to more than one department. Similarly, each department must have at least one course and a course may belong to more than one department. A professor may teach more than one student, and a student may have more than one professor.