Features

Engine

Full Rete Implementation -- with high performance indexing
Dynamic RuleBases
Stateful and Stateless Execution Modes
Async operations
Rete and Sequential Rete
Rule Agent
Optional Data Shadowing
Pluggeable Dialects

Propositional Logic

Literal Restriction
Variable Restriction
Return Value Restriction
Jointed and dis-jointed Connectives allowed - '&&' '||'
inline-Eval

First Order Logic (Quantifiers)

And
Or
Exists
Not
Accumulate
Collect
From
Forall
Nesting of any CE inside of 'and' and 'or'
Support for both infix and prefix 'and'/'or' CEs
Nesting and Chaining of 'from', 'accumulate', 'collect'

Execution Control

Conflict Resolution (salience) Now pluggeable
Agenda Filters
Agenda Groups
Activation Groups
Rule Flow
Attributes ( no-loop, lock-on-active )

Temporal Rules

Scheduler for rule duration will fire when a rule is true for X duration

Truth maintenance with Logical Insertions

Event Model

Working Memory, Agenda and Rule Flow

Configurable

All Rete optimizations and execution behavior can be configured

Authoring

Technical rules: DRL and XML formats supported
Template based DSLs
Guided Editor
BRMS and Eclipse
Decision Tables (Excel, Open Office)

BRMS (Knowledge Asset Management System)

Authoring and Storage DRLs, RuleFlows, Decision Tables, Business Rules (Guided Editor)
Multi level Versioning, at both the rule and package level
Classification
Deployment
Built on Standards and Open APIs - JCR (JSR 170) Dublin Core, GWT

More Expression flexibility

3.0.x only allows comma separated field constraints. 'or' could be used at the CE level, but resulted in subrule generation.

Can now use && and || inside the pattern for multiple values on the same field and across files – no subrule generation.
Can be as deeply nested as you like...

OLD:

Person(age > 30, age < 40 ) OR Person (hair == “black”)

NEW:

Person(age > 30 && < 40 || hair == “black”)

Auto vivification of variables in dialect

OLD:

Cheese(oldPrice : oldPrice, new Price == (oldPrice * 1.10))

NEW:

Cheese(newPrice == ( oldPrice * 1.10 ))

Drools 3.0 only supported infix 'and'/'or' constraints, which is idea for some situations but more complicated to read for others
OLD

Person(name == "matthew") or Person(name == "john")

Drools 4.0 allows for both infix and prefix:

NEW:

(or	Person(name == "matthew")
	Person(name == "john") )

3.0.x had to always declare the variable, causing clutter, can now access direct properties of pattern variables.

OLD:

p: Person (personId : id)

	i: Item (id == personId, value > 100)

NEW:

p: Person()

	i: Item(id == p.id, value > 100)

Eval rewrite for complex expressions, engine works out best way to do it – of course, flat models work best for performance.

OLD:

Person($pets : pets) eval ($pets[’rover’].type = “dog”)

NEW:

Person(pets[’rover’].type == “dog”)

More Powerful CEs

3.0:

'and'
'or'
'not' Could only nest a single Pattern
'exists’ Could only nest a single Pattern

4.0:

'forall'
‘from’
‘collect’
‘accumulate’
'not' - Now allows any nested CE
'exists' - Now allows any nested CE

Forall, true when the pattern is true for all facts

forall(Bus (color==”red”))

From, Pulls and unifies against non-working memory data ( can call Hibernate queries )

Restaurant ( rating == “fivestar” )
   from hbSession
   .getNamedQuery (”restaurant query”)
   .setProperties ([key1 : value1, key2 : value2])
   .list()

Collect - Allows you to use cardinality eg: when there are more than 6 red buses:

List(size > 6) from collect ( Bus(color == “red”) )‏

'from' can be chained. Following is true if all items in a cart have a price greater than 10

List(size == ($list.size)) from collect(Item(price > 10 )) from $cart.items Accumulate,

More powerful 'Accumulate' allows you to execute actions on each matched fact in the set

$total : Integer() from accumulate( $item : Item( )
	init(count = 0; total=0)
	action(count++;total += $item.price)

	result( return total/count )

)

You can also use multiple patterns in your 'Accumulate'

$cheesery : Cheesery( totalAmount > 30 ) 
	from accumulate( $person : Person( $likes: likes) and $cheese : Cheese( type == $likes ),
		init( Cheesery cheesery = new Cheesery(); ),
		action( cheesery.addCheese( $cheese ); ),
		reverse( cheesery.removeCheese( $cheese ); ),
		result( cheesery ) );