For the rest of this chapter, we will use a sample database called the COMPANY database to illustrate the concepts of the ER model. A department controls a number of projects, each of which has a uniq...For the rest of this chapter, we will use a sample database called the COMPANY database to illustrate the concepts of the ER model. A department controls a number of projects, each of which has a unique name, a unique number and a budget. The Spouse table, in the COMPANY database, is a weak entity because its primary key is dependent on the Employee table. A table without a foreign key or a table that contains a foreign key that can contain nulls is a strong entity
