We are waiting for the next stable version of JBoss Rules (v.4.0), which promises to offer a full access to all features already implemented in JBoss Rules 4.0 Milestone Release 2. These features convert JBoss Rules platform/rule engine into a reasonable, open-source alternative to other commercial products from the business market.

Use of && and || inside of the columns

It simplifies the syntax by allowing the construction of some filter expressions that previously were done
using predicate expressions or eval structures i.e.

$driver:Diver(age >= 16 && < 25 && location != "CA" || != "NY" )

Implicit binding for predicate and return value expressions

$driver:Driver(premium -> (numberOfAccidents * 150))
$driver:Driver(premium == (numberOfAccidents * 150))

There is no need to obtain first a variable for the attribute numberOfAccidents, in order to use it in a return value expression, like in example above. The expression is build using the directly the numberOfAccidents attribute.

Direct access to the properties of the patterns

$carModel:CarModel()
$car:Car(carBasePremium == $carModel.basePremium)

basePremium is a property of the CarModel class.

Nesting of conditional elements inside first-order logic quantifiers and negation

Existentially quantified expressions e.g. exists Car(price >= 20000 && <= 45000 )
semantically maps to the existentially quantified formula:
∃x (Car(x)∧ price(x) >= 20000 ∧ price(x) <=45000)

Universally quantified expressions e.g. forall Car(price == 45000) corresponds to the universally quantified formula:

∀x (Car(x)∧ price(x) == 45000)

Negation e.g. not Car(price >= 45000) is semanticaly the same as the following logical formula:

∀x ¬(Car(x)∧ price(x) >= 45000)

Use of this keyword, as a property for constraining a fact.

 $car:Car($carModel:carModel)
 CarModel(this == $carModel)

Support of MVEL dialect

We can specify the MVEL dialect by using the new rule attribute dialect.

// The Java dialect
rule "Young_Driver"
 when
 	$car:Car($carModel:carModel , price <= 45000, isConvertible == false)
        $carModel:CarModel(hasHighTheftProbability == false, modelType == "compact") 
 
 then
 	$carModel.setBasePremium(250);
	modify($carModel);
 end
 
// The MVEL dialect 
rule "Young_Driver"
dialect "mvel"
 when
 	$car:Car(price <= 45000, isConvertible == false)
 	$carModel:CarModel(hasHighTheftProbability == false, 
		          modelType == "compact") from $car.carModel
 then
 	$carModel.basePremium = 250;
	modify($carModel);
 end

MVEL is an expression language based on Java syntax, but having its own specific features.

• MVEL uses the from keyword to bound $carModel object variable to the carModel property of Car class.
  DRL syntax obtains the same result by using a bound variable expression (e.g. carModel == $carModel).
• Like in UML MVEL allows direct referencing to object properties i.e. a path expression such as $carModel.basePremium
  corresponds to Java setter/getter depending of the context of usage. For example $bp = $carModel.basePremium; corresponds
  to the standard getter call $bp = $carModel.getBasePremium(); but $carModel.basePremium = 250; maps into
  carModel.setBasePremium(250);).