87.5. Pricing example decisions (decision tables)

The Pricing example decision set demonstrates how to use a spreadsheet decision table for calculating the retail cost of an insurance policy in tabular format instead of directly in a DRL file.

The following is an overview of the Pricing example:

  • Name: decisiontable
  • Main class: org.drools.examples.decisiontable.PricingRuleDTExample (in src/main/java)
  • Module: drools-examples
  • Type: Java application
  • Rule file: org.drools.examples.decisiontable.ExamplePolicyPricing.xls (in src/main/resources)
  • Objective: Demonstrates use of spreadsheet decision tables to define rules

Spreadsheet decision tables are XLS or XLSX spreadsheets that contain business rules defined in a tabular format. You can include spreadsheet decision tables with standalone Red Hat Decision Manager projects or upload them to projects in Business Central. Each row in a decision table is a rule, and each column is a condition, an action, or another rule attribute. After you create and upload your decision tables into your Red Hat Decision Manager project, the rules you defined are compiled into Drools Rule Language (DRL) rules as with all other rule assets.

The purpose of the Pricing example is to provide a set of business rules to calculate the base price and a discount for a car driver applying for a specific type of insurance policy. The driver’s age and history and the policy type all contribute to calculate the basic premium, and additional rules calculate potential discounts for which the driver might be eligible.

To execute the example, run the org.drools.examples.decisiontable.PricingRuleDTExample class as a Java application in your IDE.

After the execution, the following output appears in the IDE console window: 

Cheapest possible
BASE PRICE IS: 120
DISCOUNT IS: 20

The code to execute the example follows the typical execution pattern: the rules are loaded, the facts are inserted, and a stateless KIE session is created. The difference in this example is that the rules are defined in an ExamplePolicyPricing.xls file instead of a DRL file or other source. The spreadsheet file is loaded into the decision engine using templates and DRL rules.

Spreadsheet decision table setup

The ExamplePolicyPricing.xls spreadsheet contains two decision tables in the first tab:

  • Base pricing rules
  • Promotional discount rules

As the example spreadsheet demonstrates, you can use only the first tab of a spreadsheet to create decision tables, but multiple tables can be within a single tab. Decision tables do not necessarily follow top-down logic, but are more of a means to capture data resulting in rules. The evaluation of the rules is not necessarily in the given order, because all of the normal mechanics of the decision engine still apply. This is why you can have multiple decision tables in the same tab of a spreadsheet.

The decision tables are executed through the corresponding rule template files BasePricing.drt and PromotionalPricing.drt. These template files reference the decision tables through their template parameter and directly reference the various headers for the conditions and actions in the decision tables.

BasePricing.drt rule template file

template header
age[]
profile
priorClaims
policyType
base
reason

package org.drools.examples.decisiontable;

template "Pricing bracket"
age
policyType
base

rule "Pricing bracket_@{row.rowNumber}"
  when
    Driver(age >= @{age0}, age <= @{age1}
        , priorClaims == "@{priorClaims}"
        , locationRiskProfile == "@{profile}"
    )
    policy: Policy(type == "@{policyType}")
  then
    policy.setBasePrice(@{base});
    System.out.println("@{reason}");
end
end template

PromotionalPricing.drt rule template file

template header
age[]
priorClaims
policyType
discount

package org.drools.examples.decisiontable;

template "discounts"
age
priorClaims
policyType
discount

rule "Discounts_@{row.rowNumber}"
  when
    Driver(age >= @{age0}, age <= @{age1}, priorClaims == "@{priorClaims}")
    policy: Policy(type == "@{policyType}")
  then
    policy.applyDiscount(@{discount});
end
end template

The rules are executed through the kmodule.xml reference of the KIE Session DTableWithTemplateKB, which specifically mentions the ExamplePolicyPricing.xls spreadsheet and is required for successful execution of the rules. This execution method enables you to execute the rules as a standalone unit (as in this example) or to include the rules in a packaged knowledge JAR (KJAR) file, so that the spreadsheet is packaged along with the rules for execution.

The following section of the kmodule.xml file is required for the execution of the rules and spreadsheet to work successfully: 

    <kbase name="DecisionTableKB" packages="org.drools.examples.decisiontable">
        <ksession name="DecisionTableKS" type="stateless"/>
    </kbase>

    <kbase name="DTableWithTemplateKB" packages="org.drools.examples.decisiontable-template">
        <ruleTemplate dtable="org/drools/examples/decisiontable-template/ExamplePolicyPricingTemplateData.xls"
                      template="org/drools/examples/decisiontable-template/BasePricing.drt"
                      row="3" col="3"/>
        <ruleTemplate dtable="org/drools/examples/decisiontable-template/ExamplePolicyPricingTemplateData.xls"
                      template="org/drools/examples/decisiontable-template/PromotionalPricing.drt"
                      row="18" col="3"/>
        <ksession name="DTableWithTemplateKS"/>
    </kbase>

As an alternative to executing the decision tables using rule template files, you can use the DecisionTableConfiguration object and specify an input spreadsheet as the input type, such as DecisionTableInputType.xls: 

DecisionTableConfiguration dtableconfiguration =
    KnowledgeBuilderFactory.newDecisionTableConfiguration();
        dtableconfiguration.setInputType( DecisionTableInputType.XLS );

        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();

        Resource xlsRes = ResourceFactory.newClassPathResource( "ExamplePolicyPricing.xls",
                                                                getClass() );
        kbuilder.add( xlsRes,
                      ResourceType.DTABLE,
                      dtableconfiguration );

The Pricing example uses two fact types:

  • Driver
  • Policy.

The example sets the default values for both facts in their respective Java classes Driver.java and Policy.java. The Driver is 30 years old, has had no prior claims, and currently has a risk profile of LOW. The Policy that the driver is applying for is COMPREHENSIVE.

In any decision table, each row is considered a different rule and each column is a condition or an action. Each row is evaluated in a decision table unless the agenda is cleared upon execution.

Decision table spreadsheets (XLS or XLSX) require two key areas that define rule data:

  • A RuleSet area
  • A RuleTable area

The RuleSet area of the spreadsheet defines elements that you want to apply globally to all rules in the same package (not only the spreadsheet), such as a rule set name or universal rule attributes. The RuleTable area defines the actual rules (rows) and the conditions, actions, and other rule attributes (columns) that constitute that rule table within the specified rule set. A decision table spreadsheet can contain multiple RuleTable areas, but only one RuleSet area.

図87.11 Decision table configuration

DT Config

The RuleTable area also defines the objects to which the rule attributes apply, in this case Driver and Policy, followed by constraints on the objects. For example, the Driver object constraint that defines the Age Bracket column is age >= $1, age <= $2, where the comma-separated range is defined in the table column values, such as 18,24.

Base pricing rules

The Base pricing rules decision table in the Pricing example evaluates the age, risk profile, number of claims, and policy type of the driver and produces the base price of the policy based on these conditions.

図87.12 Base price calculation

DT Table1

The Driver attributes are defined in the following table columns:

  • Age Bracket: The age bracket has a definition for the condition age >=$1, age <=$2, which defines the condition boundaries for the driver’s age. This condition column highlights the use of $1 and $2, which is comma delimited in the spreadsheet. You can write these values as 18,24 or 18, 24 and both formats work in the execution of the business rules.
  • Location risk profile: The risk profile is a string that the example program passes always as LOW but can be changed to reflect MED or HIGH.
  • Number of prior claims: The number of claims is defined as an integer that the condition column must exactly equal to trigger the action. The value is not a range, only exact matches.

The Policy of the decision table is used in both the conditions and the actions of the rule and has attributes defined in the following table columns:

  • Policy type applying for: The policy type is a condition that is passed as a string that defines the type of coverage: COMPREHENSIVE, FIRE_THEFT, or THIRD_PARTY.
  • Base $ AUD: The basePrice is defined as an ACTION that sets the price through the constraint policy.setBasePrice($param); based on the spreadsheet cells corresponding to this value. When you execute the corresponding DRL rule for this decision table, the then portion of the rule executes this action statement on the true conditions matching the facts and sets the base price to the corresponding value.
  • Record Reason: When the rule successfully executes, this action generates an output message to the System.out console reflecting which rule fired. This is later captured in the application and printed.

The example also uses the first column on the left to categorize rules. This column is for annotation only and has no affect on rule execution.

Promotional discount rules

The Promotional discount rules decision table in the Pricing example evaluates the age, number of prior claims, and policy type of the driver to generate a potential discount on the price of the insurance policy.

図87.13 Discount calculation

DT Table2

This decision table contains the conditions for the discount for which the driver might be eligible. Similar to the base price calculation, this table evaluates the Age, Number of prior claims of the driver, and the Policy type applying for to determine a Discount % rate to be applied. For example, if the driver is 30 years old, has no prior claims, and is applying for a COMPREHENSIVE policy, the driver is given a discount of 20 percent.