OpenRules, Inc. offers methodology, proven open source tools and services that enable business analysts to work in concert with software developers to create and maintain Rules-based applications with complex business and presentation logic.

Here are some guidelines to identify areas where you can use a rule engine.

1. The number of business rules is large
2. Externalize only those rules that you expect will change often
3. Externalize only those rules which the business is interested in.
4. Business Rules Visibility is important .
5. Remember this! Validation rules are typically written, maintained by IT. With Business Rules on the other hand, you should aim to involve your business analysts in writing, managing and evolving them eventually

# Agile Rules? A "conversation" with Scott Ambler
This post summarizes some discussion I and others had with Scott (a leading thinker on agile methods) on the role of business rules in agile methods

# What is Rete III?
A basic overview of the Rete III or optimized Rete algorithm invented by Charles Forgy as an improvement over the original Rete algorithm.

A Business Rule Engine is one part of a complete system for handling all the things involved in working with rules. Admittedly, it’s an important part, but it deals only with execution… which rules need to be executed in what order? The big enterprise-oriented players are concerned with a lot more… There’s all the development and testing; linking up to data sources and other applications; measuring and reporting; deployment to different computing environments; making rule maintenance easy; looking for conflicts; and so on.

While JBoss Rules 3.0.x has been a great step from its predecessor (the unfortunately named Drools) -- providing a rule editing environment, universal and existential quantifiers (the "not" A is the same as "for all" ~A), and Domain Specific Languages (DSL's) -- there were still a few things missing.