Business Rules Engines in Java and J2EE An Introduction to Drools

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Business Rules Engines in Java and J2EEAn
Introduction to Drools

• Brian Sam-Bodden
• Integrallis Software, LLC.

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Agenda

• A Simple Example Recipe Finder
• Recipe Finder Procedural Implementation
• Introducing Drools
• Drools Overview
• Recipe Finder using Drools
• Drools The Big Picture
• When and Why?
• Rules
• DRL File

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Agenda

• Rule Engine Applications
• Drools Advanced Topics
• Drools in J2EE
• JSR-94
• Domain Specific Languages
• Conclusions
• Choosing to use a Rule Engine
• Choosing a Rule Engine

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Recipe Finder Application

• Problem Given a list of Ingredients and Recipes
  determine which recipes can be prepared

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Recipe Finder - Domain

• Recipe Finder Domain Model

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Recipe Finder - Domain

• The POJOs Recipes and Ingredients
• // Ingredients
• Ingredient rice new Ingredient("rice")
• Ingredient beans new Ingredient("beans")
• // Recipes
• Recipe riceAndBeans new Recipe("Rice and
  Beans")
• riceAndBeans.addIngredient(rice)
• riceAndBeans.addIngredient(beans)

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Recipe Finder Procedural Way

• Traditional Procedural Approach
• Loop over all recipes
• check each recipe against available ingredients
• save the matching recipes

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Recipe Finder - Procedural Way

• Matching Ingredients and Recipes
• for (IteratorltRecipegt i recipes.iterator()
  i.hasNext())
• Recipe recipe i.next()
• for (IteratorltIngredientgt j
  ingredients.iterator()
• j.hasNext())
• Ingredient ingredient j.next()
• recipe.matchIngredient(ingredient)
• if (recipe.getIsComplete())
• searchResults.addMatch(recipe)

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Recipe Finder - Procedural Way

• DEMO

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Drools

• Forward Chaining Inference Engine
• Based on Rete algorithm
• Supports several languages for expressing Rules
• Created by Bob McWhirter
• Hosted at Codehaus
• Open source, LGPL
• Simple API (few classes to master)
• http//drools.org/

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Recipe Finder - Drools Way

• Basic Steps
• Define the Rules
• Create a RuleSet by loading the Rules
• Create a WorkingMemory from the RuleSet
• Assert Facts into the WorkingMemory
• Fire the Rules

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Recipe Finder - Drools Terms

• RuleSet
• Container for parsed Rules
• Working Memory
• Created from a RuleSet
• Contains Facts
• Fact
• A Java object, a POJO or JavaBean
• Facts are evaluated against the Rules

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Recipe Finder - Drools Terms

• Application Data
• Object available to the Rules that do not affect
  the Agenda
• Agenda
• The rules that apply to the current state (the
  facts) of the WorkingMemory

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Drools The Big Picture
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Recipe Finder - Rules

• 2 Rules
• IngredientMatch Rule
• Matches an ingredient to a recipe
• RecipeMatch Rule
• Collects recipes with all ingredients matched

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Recipe Finder Rules

• ltrule name"IngredientMatch"gt
• ltparameter identifier"recipe"gt
• ltjavaclassgtRecipelt/javaclassgt
• lt/parametergt
• ltparameter identifier"ingredient"gt
• ltjavaclassgtIngredientlt/javaclassgt
• lt/parametergt
• ltjavaconditiongt
• recipe.containsIngredient(ingredient)
• lt/javaconditiongt
• ltjavaconsequencegt
• if (recipe.matchIngredient(ingredient))
  
• drools.modifyObject(recipe)
  
• lt/javaconsequencegt
• lt/rulegt

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Recipe Finder Rules

• ltrule nameRecipeMatch"gt
• ltparameter identifier"recipe"gt
• ltjavaclassgtRecipelt/javaclassgt
• lt/parametergt
• ltjavaconditiongt
• recipe.getIsComplete()
• lt/javaconditiongt
• ltjavaconsequencegt
• searchResults.addMatch(recipe)
• drools.retractObject(recipe)
• lt/javaconsequencegt
• lt/rulegt

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Recipe Finder Rules

• Rules are declarative
• Follow the pattern
• IF ltconditiongt THEN ltconsequencegt
• A rule firing (execution) can change the state of
  the WorkingMemory therefore possibly triggering
  other rules to fire

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Recipe Finder DRL File

• DRL Files are XML
• Contain one or more Rules
• Several Semantic Modules Available
• Java
• Groovy
• Python

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Recipe Finder Loading the Rules

• // URL to DRL File
• URL url RecipeFinder.class
• .getResource("recipefinder.java.drl")
• // Create RuleBase
• RuleBase ruleBase RuleBaseLoader.loadFromUrl(url
  )
• //Create a Working Memory
• WorkingMemory workingMemory
• ruleBase.newWorkingMemory()

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Recipe Finder Asserting Facts

• // assert facts - ingredients
• workingMemory.assertObject(rice)
• workingMemory.assertObject(chocolateCake)
• workingMemory.assertObject(eggs)
• // assert facts - recipes
• workingMemory.assertObject(riceAndBeans)
• workingMemory.assertObject(chocolateCake)
• workingMemory.assertObject(pancakes)
• workingMemory.assertObject(rancheroEggs)

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Recipe Finder Application Data

• // create Search Results object
• SearchResults searchResults
• new SearchResults()
• // set application data Search Results
• workingMemory
• .setApplicationData("searchResults
• 
  ,searchResults)

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Recipe Finder Application Data

• workingMemory.fireAllRules()
• Output
• Using drl recipefinder.java.drl
• You can make Rice and Beans
• You can make Ranchero Eggs

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Recipe Finder Drools

• DEMO

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Rule Engines Applications

• Knowledge Discovery
• Path Optimization
• Insurance Fraud Detection
• Email Spam Filters
• Retail, Holiday Promotions
• Credit Scoring

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Drools in a J2EE Application

• Do it yourself choices
• Stateless Session Bean Approach
• MBeans
• Storing and Retrieving RuleSets
• JNDI
• Spring (JSR-94) Integration Available

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Drools in JBoss

• DEMO

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JSR-94

• Rules Engine API (javax.rules)
• Standard for Accessing Rule Engines
• JSR-94 TCK
• Technology Compatibility Kit
• J2SE or J2EE
• Does not impose a Rule Language
• API cleanly divided between
• Admin Tasks
• Runtime Tasks

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JSR-94 Example

• DEMO

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DSL Domain Specific Languages

• Drools supports Domain Specific Languages
• Enables Business Analyst and Source closer to the
  knowledge to express that knowledge
• DSL Example
• Create a Loan Logic Calculator for Mortgage
  Origination Application
• Provide a DSL so that business people can easily
  author rules

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DSL Domain Specific Languages

• ltrule name"XYZ-FicoScore"gt
• ltloansconditiongt
• ltloanslender name"XYZ Mortage" /gt
• ltloansapplicationgt
• ltloansficogt
• ltloansless-thangt680lt/loansless-thangt
• lt/loansficogt
• lt/loansapplicationgt
• lt/loansconditiongt
• ltloansactionsgt
• ltloansapplication name"messages"gt
• ltloansaddgt
• Declined by XYZ Mortgage because a FICO score
  of at least 680 is required
• lt/loansaddgt
• lt/loansapplicationgt
• lt/loansactionsgt
• lt/rulegt

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DSL Example

• DEMO

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Choosing to use a Rule Engine

• Dont use a Rule Engine if
• Problems are computationally intensive based on
  few well know rules
• If your rules are not likely to change over
  time
• You need a Rule Engine if
• Need a clean separation of business policy from
  technology
• Business constrains change rapidly

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Choosing to use a Rule Engine

• Procedural thinking execution path is predefined
• If there is no exact recipe, ill defined problems
  dealing with search, discovery and evaluation
• If it is hard to produce a flow chart or diagram
  then it is equally hard to produce a program
• Rule based programming is the only technique to
  codify expertise

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Choosing a Rule Engine

• Authoring
• Rule Language Support
• Business people friendly
• Management
• Complex decision making need to be monitored
• Deployment
• Hot Deploy
• Performance
• Rule Caching
• Pre-compilation
• Standard Compliance

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Questions?
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Shameless Plug
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Thank You

• Please fill out the speaker evaluation
• You can contact me further at bsbodden_at_integrall
  is.com

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