Preface to the Third Edition
My favorite opening line for the database courses I teach is “Probably the most misunderstood term in all of business computing is database, followed closely by the word relational.” At that point, some students look a bit smug because they are absolutely, positively sure that they know what a database is and that they also know what is means for a database to be “relational.” Unfortunately, the popular press, with the help of some PC software developers, long ago distorted the meaning of both terms, which led many businesses to think that designing a database is a task that could be left to any clerical worker who had taken a one-week course on using database software. As you will see throughout this book, however, nothing could be further from the truth.
Note: The media has given us a number of nonsense computer terms such as telephone modem (we're modulating an analog signal, not a telephone), software program (the two words mean pretty much the same thing), and cable modem and DSL modem (they're not modems; they don't modulate and demodulate analog signals; they are more properly termed codecs that code and decode digital signals). It's all in an attempt to make computer jargon easier for people to understand, but it has generally had the effect of introducing misunderstandings.
This book is intended for anyone who has been given the responsibility for designing or maintaining a relational database. It will teach you how to look at the environment your database serves and to tailor the design of the database to the environment. It will also teach you how to design the database so it provides accurate and consistent data, avoiding the problems that are common to poorly designed databases. In addition, you will learn about design compromises that you might choose to make in the interest of database application performance and the consequences of making such choices.
If you are a college instructor, you may choose to use this book as a text in an undergraduate database management course. I've been doing that for a number of years (along with SQL Clearly Explained, this book's companion volume) and find that students learn from it quite well. They appreciate the straightforward language rather than a text that forces them to struggle with overly academic sentence structures. They also like the many real-world examples that appear throughout the book.
Changes in the Third Edition
The core of this book—Parts II and III, the bulk of the content of the previous editions—remains mostly unchanged from the second edition. Relational database theory has been relatively stable for more than 30 years (with the exception of the addition of sixth normal form) and requires very little updating from one edition to the next, although it has been seven years since the second edition appeared. The major changes are the discussions of fifth and sixth normal forms. The first two case studies in Part III have been updated; the third case study is new.
The chapter on object-relational databases has been removed from this edition, as well as object-relational examples in the case studies. There are two reasons for this. First, support for objects within a relational environment has largely been provided as a part of the SQL standard rather than as changes to underlying relational database theory. Second, the direction that SQL's object-relational capabilities have taken since the second edition appeared involves a number of features that violate relational design theory, and presenting them in any depth in this book would be more confusing than helpful.
By far the biggest change, however, is the addition of the new Parts I and IV. Part I contains three chapters that provide a context for database design. Database requirements don't magically appear at the point an organization needs a database, although looking at the previous editions of this book, you might think they did. Chapter 1 presents several organizational aspects of database management, including the hardware architectures on which today's databases run, and a look at service-oriented architecture (SOA), an information systems technique in which databases, like other IT functions, become services provided throughout an organization.
Chapter 2 provides an overview of several systems analysis methods to show you how organizations arrive at database requirements. In Chapter 3 you’ll discover why we care about good database design. (It really does matter!)
Part IV provides an overview of a variety of database implementation issues that you may need to consider as you design a relational database. The topics include concurrency control (keeping the database consistent while multiple users interact with it at the same time), data warehousing (understanding issues that may arise when your operational database data are destined for data mining), data quality (ensuring that data are as accurate and consistent as possible), and XML (understanding how today's databases support XML).
The addition of Parts I and IV also make this book better suited for use as a textbook in a college course. When I used the second edition as a text in my classes, I added supplementary readings to cover that material. It's nice to have it all in once place!
The material about older data models that was presented in Chapter 3 in the second edition has been moved into an appendix. None of the material in the body of the book depends on it any longer. You can read it if you are interested in knowing what preceded the relational data model, but you won't lose anything significant in terms of relational databases if you skip it.
What You Need to Know
When the first edition of this book appeared in 1999, you needed only basic computer literacy to understand just about everything the book discussed. The role of networking in database architectures has grown so much in the past decade that in addition to computer literacy, you now need to understand some basic network hardware and software concepts (e.g., the Internet, interconnection devices such as routers and switches, and servers).
Note: It has always been a challenge to decide whether to teach students about systems analysis and design before or after database management. Now we worry about where a networking course should come in the sequence. It's tough to understand databases without networking, but at the same time, some aspects of networking involve database issues.
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