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Firstly please remember that any automated conversion will be suboptimal, and should really be a bootstrap process as the start of your migration. The reason for this is, other than class-field which maps to a literal constraint, using eval is much slow than using literal and bound variable constraints on a column - we cannot index evals. How much slower? About 10 to 20 times slower. I have tried to detail some simpler optimisations, I would work on automating these after the initial converter is built.

parameter:

<parameter identifier="foo">
    <class>Foo</class>
<parameter>

---

foo : Foo()

condition:

<java:condition>foo.getValue().equals("bar")</java:condition>

---

eval(foo.getValue().equals("bar"))

If at all possible I'd apply some further automated analysis to it converts very simple, and easy to recognise, conditions to literal and bound variable:

<parameter identifier="foo">
    <class>Foo</class>
<parameter>

<java:condition>foo.getValue().equals("bar")<java:condition>

---

foo : Foo(value == "bar")

If  "foo" is not used other than in that condition, that I'd avoid binding the column to a variable.

Its not possible to bind fields in Drools 2.x, but if you do an equality check on a parameter - that can map to a bound variable constraint. Remeber that you must declare a variable, before using it - so if it defines foo and then bar, you must correct that as appropriate.

<parameter identifier="foo">
    <class>Foo</class>
<parameter>
<parameter identifier="bar">
    <class>Bar</class>
<parameter>

<java:condition>foo.equals(bar)<java:condition>

---

bar : Bar()
foo : Foo(value == bar)

class-field:

<class-field field="name" value="A">State</class-field>

---

state : State(name == "A")

semaphore:

you will need to copy/paste old semaphore classes from drools 2.x to your own classpath

http://fisheye.codehaus.org/browse/drools/drools/drools-base/src/main/org/drools/semantics/base

Notice that the type is concatenated onto Sempahore, type="String" becomes StringSemaphore(...).

There is no value for a semaphore, that is controlled in a later java condition.

<parameter identifier="state">
    <semaphore type="String" ></semaphore>
</parameter>

---

StringSemaphore(identifier == "state")

functions:

This cannot be done in pure xslt. In Drools 2.5 basically produced a class body inside a <java:functions: block. In Drools 3.0 we now have a real function definition. So this will need to be done in two stages, maybe the first stage can produce a marked up block that can then be fixed with some regexp in the second phase - or maybe you can apply regexp search/replace within xslt.

<java:functions>
    public static boolean amHappy(Something something) {
        return something.isHappy();
    }

    public static void log(String message) {
        System.out.println(message);
    }
</java:functions>

---

function boolean amHappy(Something something) {
        return something.isHappy();
}
function void log(String message) {
        System.out.println(message);
}

duration:

This is now an attribute, which must be converted to a single long.

-

Drools 2 to 4 XML rule conversion:

I upgraded my drools 2 rules to version 4 recently, would like to share this conversion application here. you can download Converter.zip from bottom of this page.

This Converter.zip file contains one readme file and two jars:

1. Readme.htm file showing the structure and how to run;

2. The compiled class RuleConverter.jar which converts given file or directory to new one;

3. The Eclipse project jar ConvertProject.jar for anyone might be interested;

Simply run java -jar RuleConverter.jar your file, it will convert Drools 2 XML rules to version 4 XML format, the default format is XML. Please read readMe file for mroe information.

For example, the version 2 rules is :

<rule-set name="Tests assignment rules" xmlns="http://drools.org/rules"
     xmlns:java="http://drools.org/semantics/java"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <java:import>demo.Machine</java:import>
     <java:import>demo.Test</java:import>
     <java:import>demo.TestDAO</java:import>
     <java:import>java.util.Calendar</java:import>
     <java:import>java.sql.Timestamp</java:import>      
     <java:import>java.lang.String</java:import>      
     <java:functions>
          public static void setTestsDueTime(Machine machine, int numberOfDays) {
               setTestsDueTime(machine, Calendar.DATE, numberOfDays);
          } 
          
          public static void setTestsDueTime(Machine machine, int field, int amount) {
               Calendar calendar = Calendar.getInstance();
               calendar.setTime(machine.getCreationTs());
               calendar.add(field, amount);
               machine.setTestsDueTime(new Timestamp(calendar.getTimeInMillis()));
          }
     </java:functions>     

     <rule name="Tests for type1 machine" salience="100">
          <parameter identifier="machine">
               <java:class>
                    Machine
               </java:class>
          </parameter>
          <java:condition>machine.getType().equals("Type1")</java:condition>
                <java:condition>function.equals("Router")</java:condition>     
          <java:consequence>
               Test test1 = testDAO.findByKey(Test.TEST1);
               Test test2 = testDAO.findByKey(Test.TEST2);
               Test test5 = testDAO.findByKey(Test.TEST5);
               machine.getTests().add(test1);
               machine.getTests().add(test2);
               machine.getTests().add(test5);
               drools.assertObject(test1);
               drools.assertObject(test2);
               drools.assertObject(test5);
          </java:consequence>
     </rule>
     </rule-set>

The converted version 4 XML rule:

<package xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    xmlns:java="http://drools.org/semantics/java" 
    xmlns:fn="http://www.w3.org/2005/xpath-functions" 
    xmlns="http://drools.org/drools-4.0" 
    name="com.sample">
     <import name="demo.Machine"></import>
     <import name="demo.Test"></import>
     <import name="demo.TestDAO"></import>
     <import name="java.util.Calendar"></import>
     <import name="java.sql.Timestamp"></import>
     <import name="java.lang.String"></import>      
     <function name="setTestsDueTime" return-type="void">
          <parameter identifier="machine" type="Machine"></parameter>
          <parameter identifier="numberOfDays" type="int"></parameter>
          <body>
               setTestsDueTime(machine, Calendar.DATE, numberOfDays);
          </body>
     </function>
     <function name="setTestsDueTime" return-type="void">
          <parameter identifier="machine" type="Machine"></parameter>
          <parameter identifier="field" type="int"></parameter>
          <parameter identifier="amount" type="int"></parameter>
          <body>
               Calendar calendar = Calendar.getInstance();
               calendar.setTime(machine.getCreationTs());
               calendar.add(field, amount);
               machine.setTestsDueTime(new Timestamp(calendar.getTimeInMillis()));
          </body>
     </function>
     <rule name="Tests for type1 machine">
          <lhs>
               <and-conditional-element>
                    <eval>machine.getType().equals("Type1")</eval>
                                <eval>function.equals("Router")</eval>
               </and-conditional-element>
          </lhs>
          <rhs>
               Test test1 = testDAO.findByKey(Test.TEST1);
               Test test2 = testDAO.findByKey(Test.TEST2);
               Test test5 = testDAO.findByKey(Test.TEST5);
               machine.getTests().add(test1);
               machine.getTests().add(test2);
               machine.getTests().add(test5);
               drools.assertObject(test1);
               drools.assertObject(test2);
               drools.assertObject(test5);
          </rhs>
     </rule>
</package>

I only implemented XML version, but have interface for any other version, please refer the readMe file and feel free add yours.