ASA SQL User's Guide
  Designing Your Database

Introduction

While designing a database is not a difficult task for small and medium sized databases, it is an important one. Bad database design can lead to an inefficient and possibly unreliable database system. Because client applications are built to work on specific parts of a database, and rely on the database design, a bad design can be difficult to revise at a later date.

For more information, you may also wish to consult an introductory book such as A Database Primer by C. J. Date. If you are interested in pursuing database theory, C. J. Date's An Introduction to Database Systems is an excellent textbook on the subject.