Introduction

Relational databases are tricky beasts. Other kinds of commercial software are infinitely easier to understand. Word processors are really just high-tech typewriters, and it's pretty clear that the backspace key beats that little jar of white stuff cold. Spreadsheets present a familiar enough paradigm, even to non-accountants, and email is close enough to the postal system for the model to be comprehensible.

Databases are different. Other kinds of software have a real-world analogy. Sometimes, as in the Windows desktop, the analogy is a little tenuous, but the analogies are close enough; you can get there from here. But relational databases are completely artificial. They're like geometry, they can be used to build models of the real world, but they don't exist in the real world. When was the last time you poured some wine for you and your sweetie and went out on the front porch to watch the geometry frolic on the lake?

Now, I'm talking about databases here, not tables. Tables exist aplenty, from the telephone book to the dictionary. But relational databases? Nope. Uh huh. You're not going to find them frolicking on the lake, either. The card files at the library, which contain author, title, and subject files, come close to being a database but they're still separate sets of data that are only correlated by the good graces of the local librarian.

This book is about designing database systems. My intention is to give you the knowledge you need to take a messy, complex, real-world situation and turn it into an effective database design. After reading the book you still won't be able to watch the databases frolic on the lake, but if I've done my job well you'll be able to design and implement a relational model of the fish, the seagulls, and the effects of the plankton on them both.

The book is divided into three sections. Part 1, Relational Database Theory, covers the fundamental principles of the relational model. This is where the really ugly, theoretical stuff is. But don't worry; it will get easier. Part 2, Designing Relational Database Systems, examines the analysis and design process—what you should do to get from the real world to a reliable database system design. Part 3 discusses the most important aspect of a database system from a user's point of view: the user interface.

Although we'll talk about implementation issues in the next few hundred pages, this isn't a "how to program" book. There are a few coding examples, but I've kept them to a minimum, and you should be able to follow them even if you've never seen a programming language before. The database examples are based on the Northwind sample database that comes with Microsoft Access. (The version of Northwind that comes with SQL Server 7 is very similar.) By the time you're finished this book, you'll have picked up most of what you need to get started building database systems, and you'll be ready to turn to one of the sources listed in the Bibliography for the finer points of programming style. And you'll be confident that your data architecture is sound and unlikely to get you into trouble later in your project.