At least it's not another introduction to Rete book. IMHO, Friedman-Hill did an excellent job of that seven years ago. I'd be more interested in a higher level book that addressed practical applications of rules engines with some decomposition and details of unique constraints encountered in each scenario. So you get more of that, "Oh, I never thought of using it that way! How did they do it." Sort of the equivalent format of Kimball's The Data Warehouse Toolkit - Practical Techniques For Building Dimensional Data Warehouses.