Drools

An Introduction to Business Rules with JBoss Drools John Paulett October 12, 2009

Goals Introduction to “business rules” High level overview of JBoss Drools Discussion of benefits and shortcomings 10/12/2009 2

Business Rules 10/12/2009 3

Problem Domain Basic problem: how to model “business logic” In this context: “business logic” ≠ code between UI and DB “business logic” = policies of the business 10/12/2009 4

Business Logic Examples Rate calculations at insurance company ● Depends on laws, age, sex, location, previous history, desired coverage, etc. Critical lab values at hospital ● Depends on age, previous values, other lab tests, diagnose, mandates, etc. 10/12/2009 5

Business Rule Engine Type of Expert System Two types of rules: ● “Production (or Inference) Rules” – If x, then y – Often stateless ● “Reaction Rules” (Complex Event Processing) – Wait for set of events – Stateful 10/12/2009 6

Forward Chaining 1) Iterate through antecedents (if …) 2) Each time an antecedent is matched, add knowledge of consequent (then …) 3) Go to #1, until goal reached 10/12/2009 7

Rete Algorithm Naïve forward chaining does not scale well as number of rules increases Efficient implementation using directed acyclic graph representation of rules Higher memory consumption for increased speed 10/12/2009 8

JBoss Drools 10/12/2009 9

JBoss Drools Suite Guvnor – Business Rule Management System Expert – Production Rules Flow – Workflow Fusion – Complex Event Processing 10/12/2009 10

Drools Expert Core Drools product Forward chaining rules with Rete Eclipse authoring plugin 10/12/2009 11

Ways to Write Rules Technical Rule Language Custom Domain Specific Languages Guided Editor Decision Table 10/12/2009 12

Technical Rule Language rule "Hello World" when m : Message( status == Message.HELLO, myMessage : message ) then System.out.println( myMessage ); m.setMessage( "Goodbye cruel world" ); m.setStatus( Message.GOODBYE ); update( m ); end 10/12/2009 13

Custom DSLs Map “natural language” into Technical Rule Language 10/12/2009 14

Guided Editor From http://www.jboss.org/drools/drools-expert.html 10/12/2009 15

Decision Table Excel XLS based 10/12/2009 16

Drools Guvnor BRMS – Business Rule Management System Centralized knowledgebase Web-based rule authoring Versioning of rules 10/12/2009 17

Drools Guvnor Manage rules through web console From http://www.jboss.org/drools/drools-guvnor.html 10/12/2009 18

Drools Guvnor Edit rules through web console From http://www.jboss.org/drools/drools-guvnor.html 10/12/2009 19

Drools Flow Workflow management From http://www.jboss.org/drools/drools-guvnor.html 10/12/2009 20

Drools Fusion Extension to Drools Expert for temporal reasoning Detects relevant patterns in “cloud or stream of events” 10/12/2009 21

Discussion 10/12/2009 22

When To Use a Rules Engine Large set of rules, with complex branching Rules likely to change over time, likely out of sync with code changes Involve “business users” in creation & maintenance of rules 10/12/2009 23

Benefits Separates “business logic” from application code “Hot” changes of rules (no recompile) Improved performance for large rule sets Communicates rules more clearly than Java code 10/12/2009 24

Downsides New tool ● Learning curve ● Extra point of failure Overhead ● Not practical for small rule sets 10/12/2009 25

Alternatives Java Rule Engine API - JSR 94 Closed Source: ● IBM's ILOG JRules, Fair Isaac's Blaze Advisor Open Source: ● Jess, OpenRules, Zilonis, take 10/12/2009 26

References http://www.jboss.org/drools/ http://java.sun.com/developer/technicalArticles/J2SE/JavaRule.html http://java.sys-con.com/node/45082 http://herzberg.ca.sandia.gov/guidelines.shtml 10/12/2009 27

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Drools

by John Paulett on Oct 26, 2009

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