If you can bring flexibility, nimbleness, and easy maintenance to your business application by implementing a budget-friendly, bare-bones rulebase such as JBoss Rules or Jess, why would you consider spending tens of thousands more on an enterprise BRMS (Business Rule Management System)?
The first three reasons are reports, reports, and reports. When your application has hundreds or thousands of rules, reports on which rule took the most time, which rule took the least time, which object was accessed the most, which object was accessed the least, which rules accessed which objects, and so on, become absolutely necessary for optimization and debugging. Fair Isaac’s Blaze Advisor, ILOG’s JRules, and a few other high-end rule management systems provide a wealth of reports on runtime information. Unfortunately, these kinds of reports take a good deal of time and effort to instantiate into either JBoss Rules or Jess.
The fourth reason to consider an enterprise BRMS is to get a variety of ways to view the business logic and to interact with the rules. An enterprise BRMS provides a friendly GUI and accessible syntax to the business users while giving true-blue developers a more straightforward way to quickly and easily write the rules. JBoss Rules and Jess have the programmer GUI, but they don’t have the friendly interface for the business user. One could be built but not quite as easily as you might think.
The fifth reason is direct, factory support. Although support may not be important on some projects, for the project that absolutely, positively must be completed in a short period of time with the least amount of training, only the big players can provide quality personnel on a moment’s notice. Professional services aren’t cheap, but they can save your bacon when the fire has been turned up.
Yes, JBoss makes its money on providing support personnel (via partners) and not on the product, which is free. However, at this point in time, JBoss does not provide a school for independent consultants or business users, as do Fair Isaac and ILOG. JBoss does, however, maintain a list of “approved” partners. But using a list like that is kind of like fishing -- sometimes you get a keeper and sometimes you don’t.
As for Jess, you don’t get a network of service partners, so you’re absolutely at the mercy of the user community and documentation. On the upside, the Jess community is active and the documentation is really good.