Accessing Databases with JDBC - Java: How to Program Early Objects - page 1050

AuthorISBN Table
The AuthorISBN table (described in Fig. 24.7) consists of two columns that maintain
ISBNs for each book and their corresponding authors' ID numbers. This table associates
authors with their books. The AuthorID column is a foreign key —a column in this table
that matches the primary-key column in another table (that is, AuthorID in the Authors
table). The ISBN column is also a foreign key—it matches the primary-key column (that is,
ISBN ) in the Titles table. A database might consist of many tables. A goal when designing
a database is to minimize the amount of duplicated data among the database's tables. For-
eign keys, which are specified when a database table is created in the database, link the data
in multiple tables. Together the AuthorID and ISBN columns in this table form a composite
primary key . Every row in this table uniquely matches one author to one book's ISBN.
Figure 24.8 contains the data from the AuthorISBN table of the books database.

Column Description

The author's ID number, a foreign key to the Authors table.

AuthorID

The ISBN for a book, a foreign key to the Titles table.

ISBN

Fig. 24.7 | AuthorISBN table from the books database.

AuthorID ISBN AuthorID ISBN

1 0132151006 2 0133379337
2 0132151006 1 0136151574
3 0132151006 2 0136151574
1 0133807800 4 0136151574
2 0133807800 1 0133378713
1 0132575655 2 0133378713
2 0132575655 1 0133764036
1 013299044X 2 0133764036
2 013299044X 3 0133764036
1 0132990601 1 0133570924
2 0132990601 2 0133570924
3 0132990601 3 0133570924
1 0133406954 1 0132121360
2 0133406954 2 0132121360
3 0133406954 3 0132121360
1 0133379337 5 0132121360
Fig. 24.8 | Sample data from the AuthorISBN table of books .

Every foreign-key value must appear as another table's primary-key value so the
DBMS can ensure that the foreign key value is valid—this is known as the Rule of Refer-
ential Integrity . For example, the DBMS ensures that the AuthorID value for a particular