Sample Rule Definition

Rules

Rule 1 : An order for stocks of Company A is accepted only if the number of stocks is higher than 10.
Rule 2 : An order for stocks of Company B is accepted only if the stock price is higher than 100 $.
Rule 3 : An order for stocks of Company C is accepted only if the stock price is higher than 50 $ and the number of stocks is lower than 200.

Facts

The three rules above use validating orders. All three rules are based on a customer placing an order, and can be captured using a Java bean as follows.

package samples.userguide;
/**
* Represents the fact of a customer places an order 
*/
public class PlaceOrder {

       String symbol;
       int quantity;
       double price;

       public String getSymbol() {
           return symbol;
       }

       public void setSymbol(String symbol) {
           this.symbol = symbol;
       }

       public int getQuantity() {
           return quantity;
       }

       public void setQuantity(int quantity) {
           this.quantity = quantity;
       }

       public double getPrice() {
           return price;
       }

       public void setPrice(double price) {
           this.price = price;
       }
}

The result of the execution of the three rules above is either an OrderAccept or OrderReject, which can be captured using Java beans as follows.

package samples.userguide;
/**
* Order accept notification
*/
public class OrderAccept {

       private String message;

       public String getMessage() {
           return message;
       }

       public void setMessage(String message) {
           this.message = message;
       }
}            

package samples.userguide;
/**
* Order Reject Notification
*/
       public class OrderReject {

       private String reason;

       public String getReason() {
            return reason;
       }

       public void setReason(String reason) {
            this.reason = reason;
       }
}

Using the three rules, fact and result definitions above and a rule language of a rule engine, you can define new rules. WSO2 BRS is based on the JSR 94 Java Rule Specification and uses the open source Drools rule engine as the default JSR 94 provider. Shown below is how to write the rules of our example usecase using Drools rule language.

Drools Rule File

orderApprovalRules.drl

package OrderApproval;

import samples.userguide.OrderAccept;
import samples.userguide.OrderReject;
import samples.userguide.PlaceOrder;

rule "Order Approval Rule" dialect "mvel" no-loop true salience 4

when
$placeOrder : PlaceOrder( ( symbol == "Company A" && quantity > 10 ) || ( symbol == "Company B" && price > 100 ) || ( symbol == "Company C" && price > 50 && quantity < 200 ) )
then

OrderAccept orderAccept = new OrderAccept();
orderAccept.setMessage("Accepted order for: "+ $placeOrder.quantity + " stocks of "+
$placeOrder.symbol +" at$ " + $placeOrder.price);
insertLogical(orderAccept);

end

rule "Company A Order Deny Rule" dialect "mvel" no-loop true salience 3

when
not ( OrderAccept())
$placeOrder : PlaceOrder( symbol == "Company A" )
then
retract($placeOrder);
OrderReject orderReject = new OrderReject();
orderReject.setReason("An Order for stocks of Company A is accepted only if the number of stocks is higher than 10.");
insertLogical(orderReject);
end

rule "Company B Order Deny Rule" dialect "mvel" no-loop true salience 2
when
not ( OrderAccept())
$placeOrder : PlaceOrder( symbol == "Company B" )
then
retract($placeOrder);
OrderReject orderReject = new OrderReject();
orderReject.setReason("An Order for stocks of Company B is accepted only if the stock price is higher than 100 $.");
insertLogical(orderReject);
end

rule "Company C Order Deny Rule" dialect "mvel" no-loop true salience 1
when
not ( OrderAccept())
$placeOrder : PlaceOrder( symbol == "Company C" )
then
retract($placeOrder);
OrderReject orderReject = new OrderReject();
orderReject.setReason("An Order for stocks of Company C is accepted only if the stock price is higher than 50 $ and the number of stocks is lower than 200.");
insertLogical(orderReject);
end