"Pro Drools" is a Java-focused guide to declarative programming. Drools allows for this type of programming, and is therefore flexible enough to match the semantics of your problem domain. Declarative programming deals with the what is instead of the usual how to of programming languages. Therefore, just a single what is can be used to solve a variety of problems with different how to elements. The book blends theory with explanations of the inner workings of rule engines, allowing you to solve problems easily. This book captures the bigger picture of rules usage, including how it applies to testing and debugging. The latter part of the book thoroughly covers the Drools engine, discussing such topics as its syntax and integration in plain Java applications. After reading this book, you will become proficient with the various parts that compose a rule, which may be extended to lend domain-specific sense to the rule.