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Sounds complicated! But that's just the kind of thing at which relational database systems excel. The complexity is actually somewhat illusory because each of the steps just described really amounts to little more than a simple matching operation—you relate one table to another by matching values from one table's rows to values in another table's rows. This same simple operation can be exploited in various ways to answer all kinds of questions: How many different ads does each company have? Which company's ads are most popular? How much revenue does each ad generate? What is the total fee for each company for the current billing period?
Now you know enough relational database theory to understand the rest of this book, and we don't have to go into Third Normal Form, Entity-Relationship Diagrams, and all that kind of stuff. (If you want to read about such things, I suggest you begin with the works of C.J. Date or E.F. Codd.)
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