This book grew in the writing; it turns out that, despite the slightly negative tone of some of the remarks in the previous section, there’s really quite a lot of good material to cover. What’s more, the material builds. Thus, while the first few chapters might seem to be going rather slowly, I think you’ll find the pace picks up later on. Part of the point is the number of terms and concepts that need to be introduced; the ideas aren’t really difficult, but they can seem a little overwhelming, at least until you’re comfortable with the terminology. For that reason, at least in some parts of the book, I’ll be presenting the material twice—first from an informal perspective, and then again from a more formal one. (As Bertrand Russell once memorably said: Writing can be either readable or precise, but not at the same time. I’m trying to have my cake and eat it too.)
It seems appropriate to close this chapter with another quote from Bertrand Russell:[14]
I have been accused of a habit of changing my opinions ... I am not myself in any degree ashamed of [that habit]. What physicist who was already active in 1900 would dream of boasting that his opinions had not changed during the last half century? ... The kind of philosophy that I value and have endeavoured to pursue is scientific, in the sense that there is some definite knowledge to be obtained and that new discoveries can make the admission of former error inevitable to any candid mind. For what I have said, whether early or late, I do not claim the kind of truth which theologians claim for their creeds. I claim only, at best, that the opinion expressed was a sensible one to hold at the time ... I should be much surprised if subsequent research did not show that it needed to be modified. [Such opinions were not] intended as pontifical pronouncements, but only as the best I could do at the time towards the promotion of clear and accurate thinking. Clarity, above all, has been my aim.
I’ve quoted this extract elsewhere: in the preface to my book An Introduction to Database Systems (8th edition, Addison-Wesley, 2004) in particular. The reason I mention this latter book is that it includes among other things a tutorial treatment of some of the material covered in more depth in the present book. But the world has moved on; my own understanding of the theory is, I hope, better than it was when I wrote that earlier book, and there are aspects of the treatment in that book that I would frankly now like to revise. One problem with that earlier treatment was that I attempted to make the material more palatable by adopting the fiction that any given relvar has just one key, which could then harmlessly be regarded as the primary key. But a consequence of that simplifying assumption was that several of the definitions I gave (e.g., of 2NF and 3NF) were less than fully accurate. This fact has led to a certain amount of confusion—partly my fault, I freely admit, but partly also the fault of people who took the definitions out of context.
[14] The quote is from the preface to The Bertrand Russell Dictionary of Mind, Matter and Morals (ed., Lester E. Denonn; Citadel Press, 1993). I’ve edited it just slightly here.