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May 19, 2005

"Database in Depth": Principles of Relational Theory According to C. J. Date

Sebastopol, CA--Theory is practical. This is an article of faith with well-known author and database authority Chris Date. "I mention this point explicitly because so many people seem to believe the exact opposite: namely, that if something's theoretical, it can't be practical," he explains. "But the truth is that theory--at least the theory I'm talking about here, which is relational theory--is most definitely very practical indeed." Relational theory is not just theory for its own sake, Date observes; the purpose of that theory is to allow people to build systems that are one hundred percent practical.

"In fact, we don't need to look any further than the relational model itself to find the most striking possible illustration of the foregoing thesis," says Date in his latest book, Database in Depth: Relational Theory for Practitioners (O'Reilly, US $29.95). "Indeed, it really shouldn't be necessary to defend the notion that theory is practical in a context such as ours: a multibillion dollar industry totally founded on one great theoretical idea."

This one great idea--the relational model--was first introduced to the world in 1969 by E. F. Codd in his seminal paper, "Derivability, Redundancy, and Consistency of Relations Stored in Large Data Banks," and it forms the basis for all database products in wide use today. C. J. Date was one of the first to recognize the genius in Codd's vision. He became a colleague of Codd's early on, working closely with him through the formative years of the relational model and has been a strong influence in the development of the database technology that's now ubiquitous in today's world.

In Database in Depth, Date writes for experienced database practitioners or other database professionals who "are honest enough to admit they don't understand the theory underlying their own field as well as they might, or should." The fundamental ideas of the theory are quite simple, according to Date, but they're also widely misrepresented, or underappreciated, or both. "Often, in fact, they don't seem to be understood at all," he notes. To underscore this point, Date dispels many commonly held misconceptions about the relational model, explaining that:

  • The term "relational" has nothing to do with relating two tables on a common set of columns.
  • Relations are multidimensional. They're not flat. They're not two-dimensional. Don't let the term "table" mislead you.
  • Nulls are most certainly not values, even though the SQL standard calls them so.
  • Attributes of a relation can contain values of arbitrary complexity, including such things as arrays, XML documents, and even other relations.
  • Base relations do not necessarily have to be physically stored.
  • SQL is not a set-oriented language, but rather is bag-oriented.
  • An author of numerous books, Date is particularly well known for An Introduction to Database Systems (Addison-Wesley), the standard text in the field, now in its eighth edition. Date explains upfront that very little of the technical substance of Database in Depth is new: "I've said most of it before, in previous books and publications--I've just looked around and seen that it needs to be said again. But I've tried to say it differently this time: the sequence is different, the development is different, the style and treatment are different, and the intended audience is different." So, while parts of the material have appeared before in some form or another, Date states that he regards this as a totally new book for several reasons.

    First, Database in Depth is an advanced text, explains Date. The book is also meant for self-study and includes exercises to help reinforce the material. Moreover, as he adds, "My own understanding of the relational model has evolved over the years, and continues to do so. This book represents my very latest thinking on the subject; thus, if discrepancies exist between this book and previous texts (and there are a few), the treatment in this book should be taken as superseding those in earlier ones."

    Few technology professionals can afford to be without a solid grounding in the fundamentals of relational database technology, yet many today who work with database have had no formal training in relational theory. Database in Depth offers them the opportunity to learn from the master.

    "After many years working in the database community in various capacities, I've come to realize there's a real need for a book for practitioners (not novices) that explains the basic principles of relational theory in a way not tainted by the quirks and peculiarities of existing products, commercial practice, or the SQL standard," says Date. "I wrote this book to fill that need."

    Additional Resources:

    Database in Depth
    C. J. Date
    ISBN: 0-596-10012-4, 208 pages, $29.95 US, $41.95 CA
    order@oreilly.com
    1-800-998-9938; 1-707-827-7000

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