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Drools

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For the tendency of saliva to flow out of the mouth, see drooling.
Drools
Developer(s)Red Hat
Stable release
5.1 / August 2, 2010 (2010-08-02)
Repository
Written inJava
Operating systemCross-platform
TypeRules engine
LicenseASL 2
Websitehttp://www.jboss.org/drools/

Drools is a business rule management system (BRMS) with a forward chaining inference based rules engine, more correctly known as a production rule system, using an enhanced implementation of the Rete algorithm.

Drools supports the JSR-94 standard for its business rule engine and enterprise framework for the construction, maintenance, and enforcement of business policies in an organization, application, or service.

History

The Drools Project was started by Bob McWhirter in 2001 and registered at SourceForge. Drools 1.0 was never released as the limitations of a brute force linear search approach were soon realised and work started on Drools 2.0, which was loosely based on the Rete algorithm, and the project was moved to Codehaus. During the 2.0 development cycle at Codehaus Nobi Y became the project lead and moved the project to a final 2.0 release. At this point the project had become the leading Java open source rule engine with a strong community and demand had started for commercial services. In October 2005 Drools was federated into JBoss as part of their JEMS offering and rebranded JBoss Rules. In 2006 JBoss itself was acquired by Red Hat. With financial backing from JBoss the JBoss Rules rewrite was possible with a full and enhanced Rete implementation with GUI tooling. Mid 2007 the Drools name was reclaimed since after two years people were still predominantly calling it Drools and having to refer to it as "Drools aka JBoss Rules", or "Drools (JBoss Rules)" was confusing.

Drools 5

Drools version 5.0 was released on May 19, 2009. The main goals of this version are to address CEP (in a module called Fusion) and workflow capabilities (in a module called Flow).[1]

Technology

Drools is a rules engine implementation based on Charles Forgy's Rete algorithm tailored for the Java language. Adapting Rete to an object-oriented interface allows for more natural expression of business rules with regards to business objects. Drools is written in Java, but able to run on Java and .NET.

Drools is designed to allow pluggable language implementations. Currently, rules can be written in Java, MVEL, Python, and Groovy. Drools also provides for declarative programming and is flexible enough to match the semantics of the problem domain with domain specific languages (DSL) via XML using a schema defined for the problem domain. DSLs consist of XML elements and attributes that represent the problem domain.

JBoss Rules

JBoss Rules is a reasoning engine that includes a forward chaining rule engine based on Drools. JBoss Rules is the productised version of Drools; this means it comes with support that will last several years for that particular branch, with bug and essential feature back ports. For a time the Drools name was dropped in an attempt to fully establish the JBoss Rules brand as both the project and the product; however, two years later, the community was mostly still calling it Drools, so the name was reclaimed by the community for the project. The product name remains JBoss Rules.

JBoss Enterprise BRMS

JBoss Enterprise BRMS is a business rule management system and reasoning engine for business policy and rules development, access, and change management.[2] JBoss Enterprise BRMS is a productized version of Drools with enterprise-level support available. JBoss Rules is also a productized version of Drools, but JBoss Enterprise BRMS is the flagship product.[3]

Components of the enterprise version:[4]

Drools and Guvnor are JBoss Community open source projects. As they are mature, they are brought into the enterprise-ready product JBoss Enterprise BRMS.

Components of the JBoss Community version:[6]

  • Drools Guvnor (Business Rules Manager) – a centralized repository for Drools Knowledge Bases
  • Drools Expert (rule engine) – uses the rules to perform reasoning
  • Drools Flow (process/workflow), or jBPM 5 – provides for workflow and business processes
  • Drools Fusion (event processing/temporal reasoning) – provides for Complex Event Processing (CEP)
  • Drools Planner (automated planning) – optimizes automated planning, including NP-hard planning problems

Example

This example[7] illustrates a simple rule (e.g. from a .java.drl file) that is part of an implementation of a Fibonacci calculation in Drools. The rule takes as input an instance of class Fibonacci, contains a condition, and a consequence of that condition. Note that Java code can be included directly in the consequence clause within the rule syntax. This is made possible by the Java Semantic Module and Janino. 

  <rule name="Recurse" salience="10">
    <parameter identifier="f">
      <class>Fibonacci</class>
    </parameter>
    <java:condition>f.getValue() == -1</java:condition>
    <java:consequence>
      System.err.println( "recurse for " + f.getSequence() );
      drools.assertObject( new Fibonacci( f.getSequence() - 1 ) );
    </java:consequence>
  </rule>
  • CLIPS: public domain software tool for building expert systems.
  • d3web: free, open-source platform for knowledge-based systems (expert systems).
  • JESS: a rule engine for the Java platform - it is a superset of CLIPS programming language.
  • Prolog: a general purpose logic programming language.
  • OpenL Tablets: business centric rules and BRMS.
  • DTRules: a Decision Table based, open-sourced rule engine for Java.

See also

References

  1. ^ "What is new in Drools 5.0". JBoss Community.
  2. ^ "JBoss Enterprise BRMS". Red Hat.
  3. ^ "JBoss Enterprise BRMS: Answers to frequently asked questions" (PDF). JBoss Community.
  4. ^ "JBoss Enterprise BRMS Platform 5.1". Red Hat.
  5. ^ "JBoss Enterprise BRMS datasheet" (PDF). Red Hat. p. 4.
  6. ^ "Drools 5 - The Business Logic integration Platform". JBoss Community.
  7. ^ http://legacy.drools.codehaus.org/Fibonacci+Example
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