The book is divided into five parts, starting with background, definitions and cases in Part I. Concepts and the mechanics of business rules covered in Part II cover the basics in considerable detail, which are built upon in Part III, Best Practices for Expressing Rules. This part is the meat of the book. It starts with a list of dos and don'ts for rule capture and documentation, then introduces "BRS Rulespeak", which is a set of formal rules and approach for identifying, classifying, and expressing business rules. Part IV is a somewhat loose collection of advice for IT professionals (bearing in mind that business rules span both the IT and business domains), and to a minor degree delves into data models, knowledge management and how business rules directly link to business imperatives and processes. Part V digs deeply into formal logic and facts, and is an important part of this book for the practitioner. I especially liked the appendices to this part because they went even deeper into formal methods.
Although I rate this book the highest among the three I own on the subject, if you are only exploring business rules the best place to start before reading this book is Tony Morgan's "Business Rules and Information Systems: Aligning IT with Business Goals"(ISBN 0201743914). Also, Barbara Von Halle's "Business Rules Applied: Building Better Systems Using the Business Rules Approach" (ISBN 0471412937) is a worthwhile resource to be used in conjunction with this book because goes deeper into the practical aspects of implementing business rules as an enterprise initiative.
He makes the case much more compellingly for why we need the business rules approach, and then sets up a great framework for understanding how to express and organize the rule base. This is not AI style rules, and he makes it clear what the differences are.
High level assertions are backed up with theoretcial underpinnings. The book is kept easy to read with lots of illustrations and side bars with amusing rules encountered in everyday life.