SQL and Relational Theory, 2nd Edition

THE SIGNIFICANCE OF THEORY

Note: The bulk of this section consists of an abbreviated and slightly revised version of material from an interview I did in 2005 (published in my book Date on Database: Writings 2000-2006, Apress, 2006).

The relational model, whatever else it might be, is certainly a theory—so I’d like to say a few words about the significance of theory in general before getting into details of the relational model in particular. As I said in the preface to the present book, it’s an article of faith with me that theory is practical. The purpose of relational theory in particular is not just theory for its own sake; the purpose of that theory is to allow us to build systems that are 100 percent practical. Thus, I believe that, in the relational context specifically, departures from the underlying theory are A Big Mistake.

Unfortunately, however, the term “theory” has two quite different meanings. In common parlance, it’s almost pejorative—“oh, that’s just your theory.” Indeed, in such contexts it’s effectively just a synonym for opinion (and the adverb merely—it’s merely your opinion—is often implied, too). But to a scientist, the term has a very different meaning. To a scientist, a theory is a set of ideas or principles that explain some set of observable phenomena, such as the motion of the planets. Of course, when I say I it explains something, I mean it does so coherently: It fits the facts, as it were. Moreover (and very importantly), it doesn’t just explain something, ...