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?
In fact, it appears that the best procedure for good database design is to mix eight parts intuition and experience with two parts theory.
It means that when you design a database you should give preference to your own intuition and experience – and to a big extent – 80% (8 out of 10 parts). You should also take into account your theoretical knowledge of database design, but on a much smaller scale: 20% (2 parts out of 10).
In other words, intuition and experience are more important in practical database design than theoretical knowledge, and the approximate ratio of their importance is 80% vs 20%.
Here, it’s clear from the context that the total number of “parts” implied is ten: 8 + 2 = 10, and our most common numeral system is based on 10.
In some expressions with the word “parts” the implied total number might differ from 10:
We went out on a Friday night and returned three parts drunk.
To fear love is to fear life, and those who fear life are already three parts dead.
Here, the implied total is 4, because three-quarters is a fraction familiar to the English ear (see here). The meanings are “we returned 75% drunk” and “who fear love are 75% dead”.