Java™ How To Program (Early Objects), Tenth Edition

Entity-Relationship (ER) Diagram

There’s a one-to-many relationship between a primary key and a corresponding foreign key (e.g., one author can write many books). A foreign key can appear many times in its own table, but only once (as the primary key) in another table. Figure 24.9 is an entityrelationship (ER) diagram for the books database. This diagram shows the database tables and the relationships among them. The first compartment in each box contains the table’s name and the remaining compartments contain the table’s columns. The names in italic are primary keys. A table’s primary key uniquely identifies each row in the table. Every row must have a primary-key value, and that value must be unique in the table. This is known as the Rule ...