This book is a revised, upgraded, and hugely improved version of an earlier one called Logic and Databases. Although it’s effectively a brand new book, therefore, the following remarks from that earlier book are still relevant here. First, logic and databases are inextricably intertwined. The relational model itself is essentially just elementary logic, tailored to database needs. Now, if you’re a database professional, this won’t be news to you -- but you still might not realize just how much everything we do in the database world is (or should be!) affected by logic. Logic is fundamental, and everywhere. As a database professional, therefore, you owe it to yourself to understand the basics of formal logic, and you ought to be able to explain (and perhaps defend) the connections between formal logic and database technology. And that’s what this book is about. What it does is show, through a series of partly independent, partly interrelated essays, just how various crucial aspects of database technology -- some of them very familiar, others maybe less so -- are solidly grounded in formal logic. Overall, the goal is to help you realize the importance of logic in everything you do, and also, I hope, to help you see that logic can be fun.