Overview of business rules engine with specific details on JBoss's Drools.

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
10/12/2009 2

3. Business Rules
10/12/2009 3

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
10/12/2009 4

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.
10/12/2009 5

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
10/12/2009 6

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
10/12/2009 7

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
10/12/2009 8

9. JBoss Drools
10/12/2009 9

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

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

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

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
10/12/2009 13

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

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

16. Decision Table
Excel XLS based
10/12/2009 16

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

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

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

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

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

22. Discussion
10/12/2009 22

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
10/12/2009 23

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
10/12/2009 24

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

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
10/12/2009 26

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
10/12/2009 27