Appendix A. ER Diagram for Example Database
Figure A-1 is an entity-relationship (ER) diagram for the example database used in this book. As the name suggests, the diagram depicts the entities, or tables, in the database along with the foreign-key relationships between the tables. Here are a few tips to help you understand the notation:
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Each rectangle represents a table, with the table name above the upper-left corner of the rectangle. The primary-key column(s) are listed first and are separated from nonkey columns by a line. Nonkey columns are listed below the line, and foreign key columns are marked with “(FK).”
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Lines between tables represent foreign key relationships. The markings at either end of the lines represents the allowable quantity, which can be zero (0), one (1), or many (<). For example, if you look at the relationship between the Customer and Rental tables, you would say that a rental is associated with exactly one customer, but a customer may have zero, one, or many rentals.
For more information on entity-relationship modeling, please see http://en.wikipedia.org/wiki/Entity-relationship_model.
