Rule Engine & Drools

Change the title picture in the master

Rules Engine :Drools

Rule Engine Concepts and Drools Expert

Overview

• Rule
• Rule engine introduction & Working
• Why use a Rule Engine?
• ReteOO
• Introduction to Drools
• Drools Expert & Drools Rule Formats
• Drools Rule Language Details
• Drools Eclipse IDE &
• Drools Guvnor Overview
• Drools Flow Overview

2 Rules Engine :Drools

Rule
 Rule Bean
rule "Is of valid age" public class Applicant {
when
$a : Applicant( age < 18 )  Constraints private String name;
private int age;
then private boolean valid;
$a.setValid( false );  Action
end //getter and setter
methods here
}

 Constraints for above rule
Object type constraint - Applicant Object Type.
Field constraints - age < 18
 An object type constraint plus its zero or more field constraints is referred to as a
pattern.
 The process of matching patterns against the inserted data is, referred to as
pattern matching.


Rule Engine introduction & Working

The rule engine is the computer program that delivers Knowledge Representation
and Reasoning(KRR) functionality to the developer. At a high level it has three
components:
 Ontology (“Things” e.g java Classes/Beans )
 Rules
 Data


Why use a Rule Engine?

 Separates application from dynamic logic
• Rules can be modified by different groups
• No need to recompile or redeploy
• All rules are in one place

 Declarative Programming
– Readable and Anyone can easily modify rules.

 Centralization of Knowledge
- Repository of business policy

 Speed and Scalability
- Rete algorithm, Leaps algorithm


ReteOO

 Rete algorithm was invented by Dr. Charles Forgy.
 Rete algorithm can be broken into 2 parts: rule compilation and runtime
execution.
 Rule base is compiled into discrimination network.
 Discrimination network is used to filter data as it propagates through the
network.


Rete Algorithm example

rule 1
when
Cheese( $cheddar : name == "cheddar" )
$person : Person( favouriteCheese == $cheddar )
then
System.out.println( $person.getName() + " likes cheddar" );
end

rule 2
when
Cheese( $cheddar : name == "cheddar" )
$person : Person( favouriteCheese != $cheddar )
then
System.out.println( $person.getName() + " not likes cheddar" );
end


Introduction to Drools & Drools Expert

 Drools 5 introduces the Business Logic integration Platform which provides a
unified and integrated platform for Rules, Workflow and Event Processing.

 Drools consist out of several projects:
Drools Expert (rule Engine)

Drools Guvnor (Business Rule Manager)

jBPM (Process/Workflow)

Drools Fusion (event processing /temporal reasoning)

Drools Planner (automated planning)


Drools Expert & Drools Rule Format

 Drools has an enhanced and optimized implementation of the Rete algorithm for
object oriented systems called as ReteOO.
 Drools Expert is a declarative, rule based, coding environment.

 Drools Rule Formats
 Drools Rule Language (DRL)
 Domain-specific language (DSL)
 Decision tables
 Guided rule editor
 XML


Drools Rule Language(DRL)


Domain-specific language (DSL)

 DSL are written in natural language statements.
 Domain experts (such as business analysts) can validate and do changes as per
requirements.
 DSL definitions consists of transformations from DSL "sentences" to DRL
constructs.
DRL Cheese(age < 5, price == 20, type=="stilton", country=="ch")

[when]There is a Cheese with=Cheese()
DSL [when]- age is less than {age}=age<{age}
[when]- type is '{type}'=type=='{type}‘
[when]- country equal to '{country}'=country=='{country}'

There is a Cheese with
DSLR - age is less than 42
- type is 'stilton'

DRL & DSL mapping

[when]Something is {colour}=Something(colour=="{colour}")


Domain-specific language (DSL)


Domain-specific language (DSLR)


Decision table

 Decision tables are a "precise yet compact" (ref. Wikipedia) way of representing
conditional logic, and are well suited to business level rules.
 spreadsheet format (XLS), and CSV.
 Decision tables are not recommended for rules that do not follow a set of
templates, or where there are a small number of rules
 Each row in spreadsheet is a rule
 Decision tables are essentially a tool to generate DRL rules automatically


Decision tables


Guided Rule Editor


XML Rule Language


Drools Rule Language :Executing Rules



A Knowledge Base is what we call our collection of compiled definitions, such as
rules and processes, which are compiled using the KnowledgeBuilder.

 First, we will create Knowledge Builder
KnowledgeBuilder knowledgeBuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();

 Add DRL file to Knowledge Builder , it parses and compiles DRL files
knowledgeBuilder.add(drlFileAsResource, ResourceType.DRL);

 If there are no errors, we can add the resulting packages to our Knowledge Base

Collection pkgs = knowledgeBuilder.getKnowledgePackages();
knowledgeBase = KnowledgeBaseFactory.newKnowledgeBase();
knowledgeBase.addKnowledgePackages(pkgs);



 KnowledgeSession provides the way of exposing objects to be ruled.
 Stateless Knowledge Session

StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
Applicant applicant = new Applicant( “Rajesh Kumar", 16 );
ksession.execute( applicant );
assertFalse( applicant.isValid() );

 Stateful Knowledge Session

StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
Applicant applicant = new Applicant( “Rajesh Kumar", 16 );
knowledgeSession.insert(applicant);
knowledgeSession.fireAllRules();


Drools Rule Language

Knowledge base can be updated inside rule’s body
 insert()
 Inserted object will be used by rules engines inside current session
 update()
 Updates existing in working memory object for the rest of rules
 delete()
 Removed object will not be ruled on current execution


Drools Eclipse IDE

 The Eclipse based IDE provides users with an environment to edit and test rules
in various formats, and integrate it deeply with their applications.
 Required plugins
 GEF plugin , GEF is the Eclipse Graphical Editing Framework.
http://download.eclipse.org/tools/gef/updates/releases/
 Drools Eclipse IDE plugin
http://download.jboss.org/drools/release/5.4.0.Final/org.drools.updatesite/
 Defining a Drools Runtime
 Go to windows preferences
 under the Drools category,
select "Installed Drools runtimes“
 use the default jar files as included in
the Drools Eclipse plugin
by clicking "Create a new Drools 5 runtime"


Drools Guvnor Overview

 Web-based rule management, storage, editing and deployment
environment.
 Rule editing
 text, guided, decision tables, etc.
 Version control
 Categorization
 Build and deploy
 Scenarios


Guvnor Rule Editing


Guvnor Rule Deployment


Guvnor Test Scenarios


Drools Flow Overview


References

 Drools Homepage
http://www.jboss.org/drools/
 Drools Blog
http://blog.athico.com/
 Drools Chat
irc.codehaus.org #drools
 Drools Mailing List
rules-users@lists.jboss.org


Thank you

Any questions?


Rule Engine & Drools

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Rule Engine & Drools

Similar to Rule Engine & Drools (20)

Recently uploaded

Recently uploaded (20)

Rule Engine & Drools