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    <ruleService
        name="CallChargingService"
        xmlns="http://wso2.org/carbon/rules"
        targetNamespace="http://com.test/callcharging">
    <ruleSet>
        <rule resourceType="regular" sourceType="inline">
            <![CDATA[
                package callcharging

                import samples.callcharging.CallLog;
                import samples.callcharging.CallCharge;

                rule "Local Call During Daytime"
                when
                      callLog : CallLog( type == "local")
                           eval((6 < callLog.now()) && (callLog.now()< 18))
                then
                           CallCharge c = new CallCharge();
                           c.setAmount(callLog.getPeriod() * 2);
                           insertLogical(c);
                end

                rule "Local Call During Night"
                when
                      callLog : CallLog( type == "local")
                           eval((18 < callLog.now()) || (callLog.now()< 5))
                then
                           CallCharge c = new CallCharge();
                           c.setAmount(callLog.getPeriod() * 1);
                           insertLogical(c);
                end

                rule "IDD Call During Daytime"
                when
                      callLog : CallLog( type == "idd")
                           eval((6 < callLog.now()) && (callLog.now()< 18))
                then
                           CallCharge c = new CallCharge();
                           c.setAmount(callLog.getPeriod() * 6);
                           insertLogical(c);
                end

                rule "IDD Call During Night"
                when
                      callLog : CallLog( type == "idd")
                           eval((18 < callLog.now()) || (callLog.now()< 5))
                then
                           CallCharge c = new CallCharge();
                           c.setAmount(callLog.getPeriod() * 4);
                           insertLogical(c);
                end

            ]]>
        </rule>
    </ruleSet>
    <operation name="charge">
        <input wrapperElementName="callCharge" namespace="http://com.test/callCharge">
            <fact elementName="callLog" namespace="http://com.test/callCharge" type="samples.callcharging.CallLog"></fact>
        </input>
        <output wrapperElementName="callChargeRespone" namespace="http://com.test/callCharge">
            <fact elementName="callCharge" namespace="http://com.test/callCharge" type="samples.callcharging.CallCharge"></fact>
        </output>
    </operation>
</ruleService>

Before executing this sample, it is recommended that you refer Exposing Rules as Services which explains in detail the process of writing and deploying a business rule.