Example with a context:
We should conclude by saying that there is no law that says that a database is always more useful or efficient if the tables have a high degree of normalization. These issues are more subjective than objective and must be dealt with as a design issue on an ad hoc basis. In fact, it appears that the best procedure for good database design is to mix eight parts intuition and experience with two parts theory. Hopefully, our discussion of normalization has given you a general feeling for the issues involved and will provide a good jumping-off place if you decide to study these somewhat complicated issues in greater depth.
What does that really mean? Is that a play on words or something?
8+2
, which is 10, parts total,8/10
, or 80%, of which is X, and2/10
, or 20%, of which is Y. In other words, he is saying database optimization is 80% art and 20% science. The part of database performance you can control through application of generic rules is relatively small.