This book both provides a very good introduction to knowledge systems, and a good reference for the different methods and techniques associated with them.
The book starts with an introduction to basic knowledge representation, and then explains the different techniques for modeling and extracting knowledge, and for automated reasoning. The book is neatly structured in parts, covering the different area's to which knowledge engineering can be applied.
All techniques covered in the book are illustrated by various, easy to understand, examples from different problem domains. This helps the reader to understand the techniques, and shows how the techniques can be used in practice.
In general, I found that the book very easy to read and understand, and that, after having read it, it can be used very well as a reference manual. This makes the book a standard work on knowledge engineering that belongs in the book collection of every computer scientist.