Database Design and Relational Theory

Chapter 13. Additional Normal Forms

Where’s it all going to end?

—Tom Stoppard: Rosencrantz and Guildenstern Are Dead

Now, this is not the end. It is not even the beginning of the end.

—Winston Churchill: The End of the Beginning

But it is, perhaps, the end of the beginning.

To paraphrase something I said in Chapter 9, I’ve assumed so far in this book that the only dependencies we care about^[120] are ones that have to do with projection as the decomposition operator and join as the corresponding recomposition operator. I also said that, given that assumption, it followed that 5NF was the final normal form. However, I did also say, in a footnote, that there was something called “sixth” normal form or 6NF. In fact, it turns out that we can define, not just 6NF as such, but several other normal forms also, all without departing from those same assumptions regarding available decomposition and recomposition operators. Figure 13-1 (an extended version of Figure 3-3 from Chapter 3) shows how some of those additional normal forms—viz., RFNF, SKNF, and 6NF, shown in boldface italics in the figure—fit into the overall scheme of things, as it were. In this chapter, I’ll be describing those three normal forms as well as (briefly) a few more, for completeness.

Figure 13-1. The normal form hierarchy (II)

EQUALITY DEPENDENCIES

Before describing the various additional normal forms as such, I need to spend ...