
Mark Proctor and Kris Verlaenen will be at Devoxx next week, we will be co-presenting the University session "Declarative programming with Rules, Workflow and Event Processing". Monday the 8th of Dec, 09.30, room 7.
Drools is a business rule management system (BRMS) and an enhanced Rules Engine implementation, ReteOO, based on Charles Forgy's Rete algorithm tailored for the JVM. More importantly, Drools provides for Declarative Programming and is flexible enough to match the semantics of your problem domain with Domain Specific Languages, graphical editing tools, web based tools and developer productivity tools.
| Open Source | Drools has a business friendly open source license that makes it free to download, use, embed, and distribute. |
| Declarative Programming | Allow you to say "What to do" not "How to do it". |
| Accessible business rules | Drools is friendly to both developers and business users. DSLs allow developers to write almost natural language semantics for rule authors. GUIs and visual metaphors (RuleFlow, Decision tables in Spreadsheets) also reduce the gap between business and IT. A web based BRMS (Business Rule Management System) - called Guvnor - provides GUIs for managing rule assets. |
| Logic and Data Separation | Rule engines are the ultimate in logic and data de-coupling. Increases maintainability and codebase quality. |
| Speed and Scalability | The Rete algorithm, and its descendents such as Drools' Reteoo, provide speed and scalability beyond what is practical to achieve and maintain by hand. |
| Eclipse IDE | Eclipse plugin makes it easier than ever to use Drools, with intellisense auto-completion and Debug views, rule flow GUIs and more. |
| Web based Tools (Guvnor) | AJAX-based business rules management system (BRMS), built from the ground up for advanced rule authoring, version control, and management. |

Portugese DSL in action
The links up the top left provide all the info you need - Documentation, Downloads and the Wiki etc. Feature requests and bugs are tracked in the JIRA issue tracking system (its quick to create your own account). Don't forget to take a look at the LiveTrails for videos, and the blog to keep up with the latest.
Technical rules
Drools provides a rich language and advanced constructs for solving hard algorithmic problems. There is also a helpful plug in for Eclipse (IDE). Rules are (normally) written in this way in the "drl" language, which is fully documented (and many examples are available in the downloads and documentation). A deployment framework known as the "Rule Agent" can work with the BRMS, or a drools-ant task to automate deployment of rules into your runtime systems.
Business rules
For those interested in business rules, of particular interest will be:
Guvnor is provided as a separate download (it is a web based application - deployed as a 'war').