The document introduces business rules and the JBoss Drools rules engine. It discusses how business rules are used to model business logic and policies, and how Drools uses a Rete algorithm for efficient forward-chaining rule processing. Drools provides tools for authoring, managing, and executing rules through its Expert, Guvnor, Flow and Fusion components.

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

2. Goals
Introduction to “business rules”
High level overview of JBoss Drools
Discussion of benefits and shortcomings
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3. Business Rules
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4. 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
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5. 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.
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6. 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
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7. 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
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8. 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
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9. JBoss Drools
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10. JBoss Drools Suite
Guvnor – Business Rule Management
System
Expert – Production Rules
Flow – Workflow
Fusion – Complex Event Processing
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11. Drools Expert
Core Drools product
Forward chaining rules with Rete
Eclipse authoring plugin
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12. Ways to Write Rules
Technical Rule Language
Custom Domain Specific Languages
Guided Editor
Decision Table
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13. 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
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14. Custom DSLs
Map “natural language” into Technical
Rule Language
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15. Guided Editor
From http://www.jboss.org/drools/drools-expert.html
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16. Decision Table
Excel XLS based
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17. Drools Guvnor
BRMS – Business Rule Management
System
Centralized knowledgebase
Web-based rule authoring
Versioning of rules
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18. Drools Guvnor
Manage rules through web console
From http://www.jboss.org/drools/drools-guvnor.html
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19. Drools Guvnor
Edit rules through web console
From http://www.jboss.org/drools/drools-guvnor.html
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20. Drools Flow
Workflow management
From http://www.jboss.org/drools/drools-guvnor.html
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21. Drools Fusion
Extension to Drools Expert for temporal
reasoning
Detects relevant patterns in “cloud or
stream of events”
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22. Discussion
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23. 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
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24. 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
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25. Downsides
New tool
● Learning curve
● Extra point of failure
Overhead
● Not practical for small rule sets
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26. Alternatives
Java Rule Engine API - JSR 94
Closed Source:
● IBM's ILOG JRules, Fair Isaac's Blaze Advisor
Open Source:
● Jess, OpenRules, Zilonis, take
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27. 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
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