Using a rule engine provides a framework that allows to externalize business logic in a common place which in turn empower subject matter experts of the business to easily change and manage the rules. Coding such rules directly into the application makes maintenance difficult and expensive because the rules change so often. This article describes how to architect and build a service that uses Drools to provide business decisions.

Guvnor is the new name for the BRMS. The term BRMS kind of has an industry meaning that is slightly different from what we call the Drools BRMS (when we say it, we mean the repository and web tools mostly). Hence, the name Guvnor (kind of related to governance - but really, it just sounds cool). On top of that, we are extending guvnor to manage other asset types - which aren't directly related to rules (but that's another story, for another day).

Using a rules engine can lower an application's maintenance and extensibility costs by reducing the complexity of components that implement complex business logic. This updated article shows you how to use the open source Drools rules engine to make a Java™ application more adaptive to changes. The Drools project has introduced a new native rule expression language and an Eclipse plug-in, making Drools easier to use than ever before.

Drools are using RETE as an algorithm for pattern matching. It uses a network of nodes. This network/tree has one entry point and many exit points (each one represents a rule consequence). To be more precise, the network is a directed acyclic graph of nodes. The network is created when we compile rules. It is then used at runtime. We insert objects into the network. Objects propagate through the network and if they reach exit-points of the network, activations are being created. They are later on executed after we call workingMemory.fireAllRules().

Drools 4.0.4 Released