On 6 July 2011 16:37, Mark Proctor <mproctor(a)codehaus.org&gt; wrote: Duck typing is available in Java, and therefore it can be used in Drools even today, although without the syntactic sugar described by Mark. Nevertheless, a purely Java-based implementation helps to understand issues and develop a feeling about the usefulness of the proposed feature. Here are the Java classes a user might write, using class TripleSet as provided by the support for duck typing: public class Person extends TripleSet { String name; int age; Gender gender; // enum Gender { MALE, FEMALE } } public interface EatingHabits { String getLikes(); void setLikes( String value ); String getDislikes(); void setDislikes( String value ); } public interface FussyEater { } Class SessionManager which wraps a StatefulKnowledgeSession provides a little "glue" for performing "dons" in various forms. It should also be available as a global. public class SessionManager { public SessionManager( StatefulKnowledgeSession kSession ){...} public FactHandle insert( Object object ){...} public Object dons( TripleSet tripleSet, Class<?>... interfaces ){...} public FactHandle insert( TripleSet tripleSet, Class... interfaces ){...} public void insertLogical( RuleContext rContext, TripleSet tripleSet, Class... interfaces ){...} } We can insert a Person and don it with EatingHabits: Person p1 = new Person( "John", 12, Gender.MALE ); EatingHabits ehp1 = (EatingHabits)sessionMgr.dons( p1, EatingHabits.class ); ehp1.setLikes( "cheese" ); ehp1.setDislikes( "spinach" ); sessionMgr.insert( p1 ); sessionMgr.insert( ehp1 ); And here is some DRL code, followed by the resulting output: function String isa( Object object, java.lang.Class clazz ){ return object.toString() + (clazz.isInstance( object ) ? " implements " : " doesn't implement " ) + clazz.getSimpleName(); } rule showPerson salience 100 when $p: Person() then System.out.println( "Person name: " + $p.toString() ); System.out.println( isa( $p, EatingHabits.class ) ); System.out.println( isa( $p, FussyEater.class ) ); end rule showLikes when $l: EatingHabits( likes == "cheese" ) $p: Person( this == $l ) then System.out.println( $p.getName() + " likes cheese" ); end rule showDislikes when $d: EatingHabits( dislikes != null ) $p: Person( this == $d ) then System.out.println( $p.getName() + " dislikes " + $d.getDislikes() ); sessionMgr.insertLogical( kcontext, $p, FussyEater.class ); end rule gotFussyEater when $d: FussyEater() $p: Person( this == $d ) then System.out.println( $p.getName() + " is a fussy eater" ); end rule notFussyEater when $p: Person() not FussyEater( this == $p ) then System.out.println( $p.getName() + " is not a fussy eater" ); end rule removeDislikes salience -100 no-loop true when $d: EatingHabits() then modify( $d ){ setDislikes( null ) } end ======================================================= Person name: Person<John,12,MALE> Person<John,12,MALE> doesn't implement EatingHabits Person<John,12,MALE> doesn't implement FussyEater John dislikes spinach John is a fussy eater John likes cheese John is not a fussy eater John likes cheese