This document provides an overview of Drools, including its history, core functionality, and common pitfalls. It summarizes that Drools is a rule engine that was created in 2003 and has evolved through several versions to become part of the broader KIE platform. It describes Drools' rule structure and execution cycle, and highlights some common usage best practices and issues to avoid, such as overcomplicating rules or causing infinite loops. The document concludes by outlining Drools' roadmap, including a focus on cloud deployments, tooling, and language improvements.

1. DroolsBasics&Common
Pitfalls
Mauricio Salatino / JBoss - Red Hat
JUG Cork March - 2016

2. Agenda
● What is Drools?
○ Drools History
○ Rule Engine
○ DRL language
○ Execution Cycle
● KIE - Knowledge is Everything
○ KIE Platform & KIE API
● Our First Drools Project
● Drools Common Usage
● Drools Common Pitfalls
● Roadmap (7.x version)

3. AboutMe
● Senior Software Engineer @ Red Hat/JBoss
● I joined the Drools & jBPM in 2012
● Passionate about Drools & jBPM
● Author of 3 books about jBPM
● New book about Drools
○ (1st April 2016)

4. WhatisDrools? -History
● 2003: Created by Mark Proctor and Bob McWhirter
● 2005: Acquired by JBoss
● 2007: Drools 3.x introduced the first version of the Rete
OO Algorithm
● 2009: Drools 4.x focused on performance and production
ready
● 2012: Drools 5.x focused on integration and unification
of Drools, jBPM and CEP (KIE was born)
● 2014: Drools 6.x focused on infrastructure, deployment
and tooling

5. WhatisDrools?
● It depends on what you need
○ Core: lightweight Rule Engine (a library)
○ KIE Server: standalone - as a service provider
● Rule Engine -> Inference Engine
○ Data Driven -> Forward Chaining Algorithms
○ Goal Driven -> Backward Chaining Algorithms
● Change of paradigm from Imperative (Java) to Declarative

6. WhatisDrools?-RuleStructure
rule “Large Orders require approval”
//<rule attributes>
when
Order(items.size >= 10 && total >= 100000)
then
// Trigger approval process
end

7. WhatisDrools?-RuleENgineOverview

8. WhatisDrools? -RuleExecutionCycle

9. KIEPlatform
● Drools
● Drools CEP (Fusion)
● jBPM
● OptaPlanner
● KIE Server (Drools, jBPM & CEP unified server)
● Uberfire (uberfireframework.com)
○ KIE Workbench (Drools, jBPM, Optaplanner Authoring, Runtime &
monitoring)
○ KIE Drools Workbench (Drools Authoring)

10. KIEAPIs
● KieContainer
● KieBase
● KieSession
○ insert(Object)
○ retract(FactHandle)
○ update(FactHandle, Object)
○ fireAllRules() / fireAllRules(int)
● KieScanner
● kmodule.xml
Drools Specific

11. OurFirstDroolsProject
● Simple JAR Java Maven Project
● Add Maven Dependencies
○ drools-compiler
■ drools-core (transitive)
■ kie-api (transitive)
● CDI Enabled
○ cdi-api
○ weld-se-core
○ beans.xml
● KIE specific
○ kmodule.xml
■ conventions over configurations

12. RulesPower
● Any Java Model (non-intrusive)
● Filter Data (Simple Filters)
● Correlate Data (Multiple filters between patterns)
● Accumulations / Aggregations (accumulate functions)
● Inference Chain
○ Detailed Log
○ Query Data
○ Truth Maintenance System(TMS)

13. CommonPitfalls
● Start simple, don’t over complicate things
● Compare with if/else statements
● Too much logic on the RHS
● Infinite Loop
● Complex (Nested) Models - Facts VS Non-Facts
● Cross Product - DB/SQL analogy
● From/Eval executed multiple time in RHS
○ External Service Calls (Sync calls)
● Persistence

14. Roadmap(7.xseries)
● Cloud Deployments
● Tooling for the Cloud
● Self-service applications
● Different Vertical’s Packages
● API refactoring towards
○ Flexibility
○ Services
○ Composition
● Drools language improvements
● Phreak tuning and fragmentation for distribution

15. Community
● www.drools.org / www.jbpm.org
● Drools & jBPM Mailing lists
● irc.freenode.net
○ #drools
○ #jbpm
● Blogs:
○ blog.athico.com
○ salaboy.com

16. Questions?

17. RETENetwork

18. Phreak