SQL and Relational Theory, 2nd Edition

SOME REMARKS ON TERMINOLOGY

You probably noticed right away, in that bullet list of relational issues in the previous section, that I used the formal terms relation, tuple (usually pronounced to rhyme with couple), and attribute. SQL doesn’t use these terms, of course—it uses the more “user friendly” terms table, row, and column instead. And I’m generally sympathetic to the idea of using more user friendly terms, if they can help make the ideas more palatable. In the case at hand, however, it seems to me that, regrettably, they don’t make the ideas more palatable; instead, they distort them, and in fact do the cause of genuine understanding a grave disservice. The truth is, a relation is not a table, a tuple is not a row, and an attribute is not a column. And while it might be acceptable to pretend otherwise in informal contexts—indeed, I often do so myself—I would argue that it’s acceptable only if we all understand that the more user friendly terms are just an approximation to the truth and fail overall to capture the essence of what’s really going on. To put it another way: If you do understand the true state of affairs, then judicious use of the user friendly terms can be a good idea; but in order to learn and appreciate that true state of affairs in the first place, you really do need to come to grips with the formal terms. In this book, therefore, I’ll tend to use those formal terms (at least when I’m talking about the relational model as opposed to SQL), and I’ll give precise ...