Rules Engine ? What is this ? When to use ? RETE algorithm Rules Engine In Java - JBoss Drools - features - Syntax Rules Engine In ruby - ruleby

1. Rule Engine– Java & Ruby
Drools & Ruleby
Ing. Martín Cabrera
martin.cabrera@moove-it.com
Moove-IT

2. Content
 Rules Engine ? What is this ?
 When to use ?
 RETE algorithm
 In Java - JBoss Drools
 features
 Syntax
 In ruby ?

3. Motor de Reglas ¿what a #@!$ ?
Application
Rule engine
Rule def.
knowledge base
Rule def

4. When to use?
 Infrastructure decoupled from the source
 System to allow the final user to define their rules
and change them dynamically
 Developers are not the primary responsibility for changing
rules
 Moderate or high complexity of business rules
 Performance !
 Conclusion: down the rules of your system, so that
they can be reused, decouple the code and allow the
user to know the rules ... to modify !

5. Tipical Code
01 if ((user.isMemberOf(AdministratorGroup) && user.isMemberOf(teleworkerGroup)) ||
02 user.isSuperUser() {
03 // more checks for specific cases
04 if ((expenseRequest.code().equals("B203") ||
05 (expenseRequest.code().equals("A903") && (totalExpenses < 200) &&
06 (bossSignOff > totalExpenses)) && (deptBudget.notExceeded)) {
07 // issue payments
08 }
09 else if {
10 // check lots of other conditions
11 }
12 }
Change this rules ! ... %&”@ !
13 else {
14 // even more business logic
15 }
16 }

6. Rete Algorithm – the
Solution !
 Pattern matching algorithm for implementing
production rule systems (wikipedia)
 http://en.wikipedia.org/wiki/Rete_algorithm
 replaces if ... Then with an optimized logic network

7. Rete 2
 RETE – characteristics:
 It reduces or eliminates certain types of redundancy through the use of
node sharing.
 It stores partial matches when performing joins between different fact
types.
 It allows for efficient removal of memory elements when facts are
retracted from working memory.
 Widely used to implement matching functionality within pattern-
matching engines that exploit a match-resolve-act cycle to
support forward and backward chaining and inferencing.
 Forward-chaining (facts -> goals)
 Backguard chaining (goals -> facts)

8. Drools –
 http://jboss.org/drools
 Introduction video -
http://blog.athico.com/2010/03/fosdem-50-minute-introduction-into.h
 Introduction
 Rules engine framework for java
 It is used in other jboss projects like JBPM, SEAM, Jboss ESB and
others
 The rules can be written in Java, Python, Groovy Ruby and your own
rule language
 Jboss tools – plugin Eclipse to use this framework

9. Eclipse & Drools

10. Syntax or rules definition
rule “<name>”
<attribute> <value>
when
<LHS>
then
<RHS>
end

11. Example – rule definition
rule.drl
package com.mooveit.rule
import com.mooveit.rule.Global
global Global global;
rule "r1 - first rule"
when
instance : Entity( field1 > 2010)
then
...
end

12. Example
Business Action
1
StatefulSession session = getRulesBase().newStatefulSession();
session.setGlobal("rulesImpl", this);
session.insert(instance);
session.fireAllRules();
2
3 knowledge base
+instance
Execute the “then” part for the instance that match the facts

13. Drools Schema
Rules files
Repository of
instances
assert
modify
retract

14. JBoss Rules Overview
Agenda
Rule Activation
Rule
Rule 1.Parse DRL RuleBase Rule Fact
Rule
Rule
Activation
Fact
2. Create
Rule Fact
Fact
Fact
Fact 3. Assert Facts WorkingMemory
Fact
Fact Fact
Fact
Fact
es
Fact
ul
R
Fact
ll
A
re Rule (5) activation
Fi
Rule -> consequence
4.
Rule
Rule
Rule

15. Examples in our projects
 (demo)

16. Rule Engine in

17. Rules Engine In ruby
 Ruleby - https://github.com/codeaspects/ruleby
 Rule engine for Ruby
 Active project but with few people dedicated
 October 11 of 2010 last push in the master branch
 Install: gem install ruleby
 Others
 Ruby Rools - http://rools.rubyforge.org/
 Last activity (ago 2009 in rools users)
 Status: Beta
 2 members
 A few projects without activity: rein, ruby-rules
 Treetop
 language for describing languages
 It's not a pure rule engine ... but can serve

18. Ruleby Description
 Provide a pure Ruby Domain Specific Language (DSL)
rule [m.status == :HELLO] do |v|
puts v[:m].message
end
 (LHS) Left hand side of the production (the ‘when’) is
represented by the Array parameter
 (RHS) The right hand side (the ‘then’) is represented by the
block.
engine :hello_engine do |e|
HelloWorldRulebook.new(e).rules
assert e, Message.new(:HELLO, ‘Hello World’)
e.match
end
 Result:Hello World

19. Ruleby links
 The Ruleby DSL for more information.
 https://github.com/codeaspects/ruleby/wiki/The-Ruleby
 Download
 http://gemcutter.org/gems/ruleby
 User Group
 http://groups-beta.google.com/group/ruleby

20. That's it !