External Rules Coming from XML files

Simple rule project with external rules defined in XML.


Rule Project "ExternalRulesFromXML"

Step 1. Setting Up Rule Templates

Step 2. Defining Rule Tables in XML

Step 3. Reading XML rules in Java

Step 4. Creating and Executing Rules from a Java Program

OpenRules allows you to keep your business rules in XML files that correspond to the columns (conditions and actions) of Excel's templates based on which the proper rule tables will be executed.  While you may use any XML processing software, this sample project demonstrate how to use a simple XML interface provided by OpenRules.

This project intends to produce greetings like "Good Morning, Mrs. Robinson!" based on the current time and different customer's attributes such as gender and marital status. In a way it is similar to the standard project "HelloJavaTemplates" but instead of using Excel-based rule tables it is using XML-based rule tables.

Step 1. Setting Up Rule Templates       top

The business logic for producing greetings and salutations is presented in the Excel file HelloTemplates.xls. The first template

Rules void defineGreeting(App app, int hour)
C1 C2 A1
min <= hour hour <= max app.greeting =  greeting; 
int min int max String greeting
Hour From Hour To Set Greeting
    Unknown Greeting

specifies how to define different greetings (Good Morning, Good Afternoon, etc.) based on the hour of the day. If the parameter "hour" belongs to the interval [min;max] defined by a concrete rule then the attribute "greeting" of the parameter "app" will be set to the proper greeting. If no rules are satisfied, this multi-hit table will use the default greeting "Unknown Greeting". 

The second template

Rules void defineSalutation(App app, Customer c)
C1 C2 C3 A1
c.gender.equals(gender) c.maritalStatus.equals(status) c.age < age app.salutation = salutation; 
String gender String status int age String salutation
Gender Marital Status Age Less Than Set Salutation
      Unknown Salutation

specifies how to define different salutations (Mr., Mrs., etc.) based on customer attributes Gender, Marital Status, and Age. If no rules are satisfied, this multi-hit table will use the default salutation "Unknown Salutation". 

Step 2. Defining Rule Tables in XML    top

You may create a subdirectory "xml" in the directory "rules" and place different xml-files into it.  The first file "GreetingRules.xml" defines a rule table with the name "greetingRules" that will be based on the template with the name "defineGreeting":

<?xml version="1.0" encoding="UTF-8"?>

<GreetingRules ruleTableName="greetingRules" templateName="defineGreeting" type="Array of Rule(s)">

  <Rule from="0" to="11" greeting="Good Morning" />
  <Rule from="12" to="16" greeting="Good Afternoon" />
  <Rule from="17" to="21" greeting="Good Evening" />
  <Rule from="22" to="24" greeting="Good Night" />


Similarly we create the second file "SalutationRules.xml":

<?xml version="1.0" encoding="UTF-8"?>

<SalutationRules ruleTableName="salutationRules" templateName="defineSalutation">























Please note that the last rule contains an extra attribute "maxAge". OpenRules does not require any specification of the XML document and will dynamically recognize its structure.

Step 3. Reading XML rules in Java      top

To inform an OpenRulesEngine about external rules, you to create an object of the type ExternalRules and add to it all external RuleTables. Each instance of the class RuleTable consists of:

- rule table name (String)

- template name (String)

- a grid of objects that represent the content of a rule tables (Object[][])

In this project, we will create an instance of the class External Rules directly in the Excel method "getExternalRules":

Method ExternalRules createExternalRules()
ExternalRules externalRules = new ExternalRules();
return externalRules;

This method will execute two other methods "addGreetingRules" and "addSalutationRules" that will read the above xml-files and will add the proper rule tables to the newly create ExternalRules object.

Before reading the xml files we have to specify the proper xml schemas in the Environment table placed in the main Excel file HelloXMLRules.xls:

import.java com.openrules.table.external.Objects
import.schema file:rules/xml/GreetingRules.xml

OpenRules dynamically defines the Java classes GreetingRules and SalutationRules  that will be used to read the proper XML files.

Now we may specify the method "addGreetingRules":

Method ExternalRules addGreetingRules(ExternalRules externalRules)
GreetingRules greetings = GreetingRules.load("file:rules/xml/GreetingRules.xml");
Objects[] grid = new Objects[greetings.Rule.length];
for(int i = 0; i < greetings.Rule.length; ++i) {
   GreetingRules.Rule r = greetings.Rule[i];
   Objects row = new Objects(3);
   row.set(0,r.from); row.set(1,r.to); row.set(2,r.greeting);
   grid[i] = row;
externalRules.addRuleTable(greetings.ruleTableName, greetings.templateName, grid );

First we load the rules from the xml-file defining its relative path using the standard OpenRules URL notation:


All objects specified in the file GreetingRules.xml becomes available to the Java code through the object "greetings" of the dynamically defined type GreetingRules. In particular, the object "greetings.Rule" points to the array of objects of the dynamic type "Rule" as it was defined in the xml-file.

Then we create a "grid" as an array of the predefined type Objects that is used by OpenRules to simplify handling of multi-dimensional array. Looping through all elements of the array greetings.Rules we are adding new rows to the object "grid". Data elements inside each rule are available through their names defined in the xml-file: r.from, r.to, r.greeting. 

Similarly we specify the method "addSalutationRules":

Method ExternalRules addSalutationRules(ExternalRules externalRules)
SalutationRules salutations = SalutationRules.load("file:rules/xml/SalutationRules.xml");
Objects[] grid = new Objects[salutations.Rule.length];
for(int i = 0; i < salutations.Rule.length; ++i) {
   SalutationRules.Rule r = salutations.Rule[i];
   Objects row = new Objects(4);
   row.set(0,r.gender); row.set(1,r.maritalStatus); row.set(2,r.maxAge); row.set(3,r.salutation);
   grid[i] = row;
externalRules.addRuleTable(salutations.ruleTableName, salutations.templateName, grid );

Step 4. Creating and Executing Rules from a Java Program     top

All other modules are typical for basic rule projects. The main Java file RunExternalRulesFromXML.java is used to test the above rules:

import com.openrules.ruleengine.ExternalRules;
import com.openrules.ruleengine.OpenRulesEngine;

public class RunExternalRulesFromXML {

	public static void main(String[] args)
		// The first engine reads XML-based rules described at HelloXMLRules.xls
		String xlsMainData = "file:rules/main/HelloXMLRules.xls";
	        OpenRulesEngine engine1 = new OpenRulesEngine(xlsMainData);
		ExternalRules externalRules = (ExternalRules) engine1.run("createExternalRules");
		// Print External Rules
		for (int i = 0; i < externalRules.getRuleTables().size(); i++) {

		// The second engine reads test data and execute external rules created by the first engine
		String fileName = "file:rules/main/HelloCustomer.xls";
		OpenRulesEngine engine2 = new OpenRulesEngine(fileName,externalRules);
		App app = (App) engine2.run("getDefaultApplication");
		System.out.println("\nGenerated Greeting:");

The first instance 'engine1" of the class OpenRulesEngine is based on the main Excel-file HelloXMLRules.xls. We execute the method "createExternalRules" to create external rules from the xml files:

ExternalRules externalRules = (ExternalRules) engine1.run("createExternalRules");

The second instance "engine2" of the OpenRulesEngine is using the main Excel-file HelloCustomer.xls and newly created external rules:

OpenRulesEngine engine2 = new OpenRulesEngine(fileName,externalRules);

The main file HelloCustomer.xls defines the Environment as follows:

import.java hello.*
import.static com.openrules.tools.Methods
include ../include/HelloTemplates.xls
include ../include/HelloData.xls

This application uses two simple Java beans:


String name;

String maritalStatus;

String gender;

int age;


Customer customer;

String greeting;

String salutation;

String result;

The proper instance of the Customer and App are created based on the Excel file HelloData.xls using these data tables:

Data App apps
customer.name customer.maritalStatus customer.gender customer.age
Customer Name Marital Status Gender Age
Robinson Married Female 24
Smith Single Male 19
Method App getDefaultApplication()  
return apps[0];  

And finally, the engine2 will execute rules by calling the method "run":


The proper method "generateGreeting" is described in the file HelloCustomer.xls in the following table:

Method void generateGreeting(App app) 
int hour = Calendar.getInstance().get(Calendar.HOUR_OF_DAY);
greetingRules(app, hour);
salutationRules(app, app.customer);
app.result = app.greeting + ", " + app.salutation + " " + app.customer.name + "!";

You may validate the entire rule project by double-clicking on the file "compile.bat".  Because the actual external rule tables "greetingRules" and "salutationRules" will become known only in run-time the proper OpenRules validator may produce errors (warnings) about unknown rule tables. You may ignore these errors or you may explicitly inform OpenRules about this fact by adding an optional table to the file HelloCustomer.xls:

greetingRules defineGreeting
salutationRules defineSalutation

To run the project you may double-click on the file "run.bat". Here is an expected output:

INITIALIZE OPENRULES ENGINE 5.3.0 (build 03092009) for [file:rules/main/HelloXMLRules.xls]
ExternalRules greetingRules template defineGreeting
0 11 Good Morning 
12 16 Good Afternoon 
17 21 Good Evening 
22 24 Good Night 

ExternalRules salutationRules template defineSalutation
Female Married null Mrs. 
Female Single null Ms. 
Male  null Mr. 
Male Single 5 Little 

INITIALIZE OPENRULES ENGINE 5.3.0 (build 03092009) for [file:rules/main/HelloCustomer.xls]
External rules table: greetingRules
External rules table: salutationRules
[../include/HelloTemplates.xls] has been resolved to [file:<..>/ExternalRulesFromXML/rules/include/HelloTemplates.xls]
[../include/HelloData.xls] has been resolved to [file:<..>/ExternalRulesFromXML/rules/include/HelloData.xls]

Generated Greeting:
Good Afternoon, Mrs. Robinson!






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