This topic 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 topic, 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: 12
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 topic An Introduction to Database Systems (8th
edition, Addison-Wesley, 2004) in particular. The reason I mention this latter topic is that it includes among other
things a tutorial treatment of some of the material covered in more depth in the present topic. But the world has
moved on; my own understanding of the theory is, I hope, better than it was when I wrote that earlier topic, and
there are aspects of the treatment in that topic 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.
The purpose of these exercises is to give some idea of the scope of the chapters to come, and also perhaps to test the
extent of your existing knowledge. They can't be answered from material in the present chapter alone.
Is it true that the relational model doesn't require relvars to be in any particular normal form?
Should data redundancy always be eliminated? Can it be?
12 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.