Book Image

Drools JBoss Rules 5.X Developer's Guide

By : Michal Bali
Book Image

Drools JBoss Rules 5.X Developer's Guide

By: Michal Bali

Overview of this book

<p>Writing business rules has always been a challenging task. Business rules tend to change often leading to a maintenance nightmare. This book shows you various ways to code your business rules using Drools, the open source Business Rules Management System.<br /><br />Drools JBoss Rules 5.X Developer's Guide shows various features of the Drools platform by walking the reader through several real-world examples. Each chapter elaborates on different aspects of the Drools platform. The reader will also learn about the inner workings of Drools and its implementation of the Rete algorithm.<br /><br />The book starts with explaining rule basics, then builds on this information by going through various areas like human readable rules, rules for validation, and stateful rules, using examples from the banking domain. A loan approval process example shows the use of the jBPM module. Parts of a banking fraud detection system are implemented with the Drools Fusion module which is the complex event processing part of Drools. Finally, more technical details are shown detailing the inner workings of Drools, the implementation of the ReteOO algorithm, indexing, node sharing, and partitioning.</p>
Table of Contents (22 chapters)
Drools JBoss Rules 5.X Developer's Guide
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Setting Up the Development Environment
Creating Custom Operators
Dependencies of Sample Application
Index

Left and right unlinking


This is another feature of Drools that helps to reduce the amount of memory, especially for large knowledge bases with lots of rules. Its principle is simple. As we know, beta nodes have left and right memory, every time a fact propagates, it is added to the right memory, and every time a tuple propagates, it is added to the left memory. However, if a fact/tuple is being propagated and the opposite left/right memory is empty, there can't be any match. The fact/tuple would normally enter the right/left memory and it would wait there until the opposite memory gets filled, so a match can be attempted. What Drools can do instead is that it can unlink the current (left or right) memory. This will save us unnecessary node memory population. Then, in case the opposite memory gets populated, the unlinked side gets linked back and receives all the propagations that were left out.

Note that this feature is turned off by default and you have to explicitly enable it by setting...