This document discusses using rules engines for business logic and provides examples of real-world use cases. It begins with an overview of what rules engines are and how they work, explaining concepts like facts, conditions, actions, and rules. It then discusses different types of rules engines and rule processing algorithms like the basic and Rete algorithms. The document provides code snippets and XML examples from real client-side rules engines developed for applications in domains like forms building, order management, and government benefits applications. It demonstrates how rules engines can externalize and manage complex business rules and workflows.

2. What is a rules engine?

8. How are rules defined and implemented?

9. Typical workflow from business to technology The organization defines the business processes.

10. Typical workflow from business to technology A business analyst translates business practices into business rule statements, constraints and actions.

11. Typical workflow from business to technology The software developer implements the rules engine component in the application. The actions and triggers are implemented by the developer. The application is deployed by a developer with the rules externalized

12. Typical workflow from business to technology The organization changes some business processes.

13. Typical workflow from business to technology If the business process doesn’t require new actions, anyone, including this silly intern with a small desk, can update the rules engine. Win.

15. How do rules engines work?

19. Examples!

23. The Stack...

24. The Rules... < rule id = &quot;isFemale&quot; > < statement ><![CDATA[ @info.sex equalTo 'Female' ]]></ statement > < actions > < visibleAction questionIDs = &quot;areYouPregnant&quot; /> </ actions > </ rule > < rule id = &quot;isTeenager&quot; > < statement ><![CDATA[ @info.age greaterThanOrEqualTo '13' AND @info.age lessThan '18' ]]></ statement > < actions > </ actions > </ rule > < rule id = &quot;isTeenageGirl&quot; > < statement ><![CDATA[ $isTeenager AND $isFemale ]]></ statement > < actions > < urlAction url = &quot; http://www.seventeen.com &quot; /> </ actions > </ rule >

25. Regular Expressions public static var andOrTrueFalsePattern:RegExp = /AND|OR|true|false/ gi; public static var ruleTokenPattern:RegExp = /([a-zA-Z0-9_]+)/ g; public static var propertyTokenPattern:RegExp = /([a-zA-Z0-9_.]+)/ g; public static var nonSpaceGroups:RegExp = /([a-zA-Z0-9_.'&quot;]+)([^ ])/ gi; public static var quotesPattern:RegExp = /'|&quot;/ gi;

26. Pattern matching a rule...

28. Hamcrest API - Matchers: public static const EQUAL_TO:String = &quot;equalTo&quot; ; public static const NOT_EQUAL_TO:String = &quot;notEqualTo&quot; ; public static const LESS_THAN:String = &quot;lessThan&quot; ; public static const LESS_THAN_OR_EQUAL_TO:String = &quot;lessThanOrEqualTo&quot; ; public static const GREATER_THAN:String = &quot;greaterThan&quot; ; public static const GREATER_THAN_OR_EQUAL_TO:String = &quot;greaterThanOrEqualTo&quot; ; public static const CONTAINS:String = &quot;contains&quot; ;

29. Hamcrest API: Get your facts straight! public static function evaluateCondition(target:*, operator:String, source:*):Boolean { try { switch (operator) { case Matchers.EQUAL_TO: assertThat(target, equalTo(source)); break ; case Matchers.NOT_EQUAL_TO: assertThat(target, not(equalTo(source))); break ; case Matchers.LESS_THAN: assertThat(Number(target), lessThan(Number(source))); break ; default : throw new RuleError( &quot;No matcher found for this operator!” ); } } catch (e:Error) { if (e.errorID != RuleError.ILLEGAL_OPERATOR_ERROR) { value= false ; } else { _logger.error(e.message, e.errorID); } }

35. Basic Algorithm Fact condition A Action Fact cB cC cD AND OR Fact Optimizations can give priority to certain conditions, wait to process until all facts are run through conditions, etc.

46. Rule XML Sample <!-- Rule definition --> < rule > < getValue key = &quot;Metal Quality&quot; >< containsString value = &quot;Gold&quot; /></ getValue > < addValueOption key = &quot;Metal Finish&quot; value = &quot;Gold-on-Gold&quot; meta = &quot;code:2&quot; /> </ rule >

47. Macro XML Sample: pricing a stone <!-- Macro definition --> < defineMacro name = &quot;priceStone&quot; > < rule > < allOf > < getValue key = &quot;$stoneKey&quot; >< equalTo value = &quot;$stoneValue&quot; /></ getValue > < getValue key = &quot;$stoneSizeKey&quot; >< equalTo value = &quot;$stoneSizeValue&quot; /></ getValue > </ allOf > < addPrice label = &quot;$stoneKey: $stoneValue&quot; amount = &quot;$amount&quot; /> </ rule > </ defineMacro > <!-- Macro implementation --> < priceStone stoneKey = &quot;Royal Stone&quot; stoneValue = &quot;Birthstones - Alexandrite (Jun)&quot; stoneSizeKey = &quot;Royal Stone Size&quot; stoneSizeValue = &quot;12 Point&quot; amount = &quot;4208&quot; />

54. GBA Rules engine architecture Fact (change event) Conditions Actions User Questions Data Model Binding! Binding! Binding!

56. Question XML < question id = &quot;362&quot; controlType = &quot;ComboBox&quot; inlineHelp = &quot;Does anyone receive money from elsewhere?&quot; label = &quot;Other Employment&quot; optionsID = &quot;R00013&quot; target = &quot;Household.Income.OtherIncome&quot; />

58. Rule XML < rule id = &quot;doesAnyoneHasOtherEmployment&quot; > < statement > $hasOtherEmployment </ statement > < actions > < visibleAction questionGroupIDs = &quot;income_other&quot; /> </ actions > </ rule > < rule id = &quot;NoEmployment&quot; > < statement > $IsOnStrike OR ($NoFutureEmployment AND $NoCurrentEmployment AND $NoPastEmployment AND $NoOtherIncome) </ statement > < actions > < visibleAction questionIDs = &quot;364&quot; /> </ actions > </ rule >

59. Data Abstraction

65. Thanks for obeying. Drew McLean twitter: TunnelVisionary [email_address] RJ Owen twitter: rjowen [email_address]