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
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
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."
Database in Depth
C. J. Date
ISBN: 0-596-10012-4, 208 pages, $29.95 US, $41.95 CA
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