http://blog.athico.com/2011/06/truth-maintenance-over-directed-graphs.html ------- Truth Maintenance over Directed Graphs using Reactive Derivation Queries <http://blog.athico.com/2011/06/truth-maintenance-over-directed-graphs.htm... Posted by Mark Proctor Drools 5.2 is almost done and we have something very cool added. As previous blogs have mentioned, we recently added positoinal syntax and prolog like derivation query based backward chaining <http://blog.athico.com/2011/04/backward-chaining-emerges-in-drools.html>;. However those queries were pull only and didn't support the recently added live "open queries" <http://blog.athico.com/2010/05/live-querries.html>;. It also had the problem that it was method recursion based, so could blow the method stack if it was too deep. 5.2 is now stack based and supports "open queries", you just miss of the '?'. So what this means is you can have TMS over reactive derivation queries. If I have a key in an envelop on a desk in an office I can add a TMS justifcation that will only exist while the key remains in the office. This should have some very interesting use cases and I look forward to seeing what people come up with. For instance you could create a rule to monitor a project's maven dependencies and transititive depdencies and receive an alert if ASL/MIT/BSD project has a GPL dependency added via a transititive dependency. It's a bit abstract, but here is the unit test showing it working: package org.drools.test import java.util.List import java.util.ArrayList import org.drools.Person global List list dialect "mvel" declare Location thing : String location : String end query isContainedIn( String x, String y ) Location(x, y;) or ( Location(z, y;) and isContainedIn(x, z;) ) end rule look when Person( $l : likes ) isContainedIn( $l, 'office'; ) then insertLogical( 'blah' );end rule existsBlah when exists String( this == 'blah') then list.add( 'exists blah' );end rule notBlah when not String( this == 'blah') then list.add( 'not blah' );end rule init when then insert( new Location("apple", "kitchen") ); insert( new Location("desk", "office") ); insert( new Location("flashlight", "desk") ); insert( new Location("envelope", "desk") ); insert( new Location("key", "envelope") ); insert( new Location("washing machine", "cellar") ); insert( new Location("nani", "washing machine") ); insert( new Location("broccoli", "kitchen") ); insert( new Location("crackers", "kitchen") ); insert( new Location("computer", "office") ); end rule go1 when String( this == 'go1') then list.add( rule.getName() ); insert( new Location('lamp', 'desk') ); end rule go2 when String( this == 'go2') $l : Location('lamp', 'desk'; ) then list.add( rule.getName() ); retract( $l ); end rule go3 when String( this == 'go3') then list.add( rule.getName() ); insert( new Location('lamp', 'desk') ); end rule go4 when String( this == 'go4') $l : Location('lamp', 'desk'; ) then list.add( rule.getName() ); modify( $l ) { thing = 'book' }; end rule go5 when String( this == 'go5') $l : Location('book', 'desk'; ) then list.add( rule.getName() ); modify( $l ) { thing = 'lamp' }; end rule go6 when String( this == 'go6') $l : Location( 'lamp', 'desk'; ) then list.add( rule.getName() ); modify( $l ) { thing = 'book' }; end rule go7 when String( this == 'go7') $p : Person( likes == 'lamp' ) then list.add( rule.getName() ); modify( $p ) { likes = 'key' }; end ----- [go1, exists blah, go2, not blah, go3, exists blah, go4, not blah, go5, exists blah, go6, not blah, go7, exists blah] ----- Person p = new Person(); p.setLikes( "lamp" ); FactHandle handle = ksession.insert( p ); ksession.fireAllRules(); list.clear(); FactHandle fh = ksession.insert( "go1" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go1", list.get(0)); assertEquals( "exists blah", list.get(1)); fh = ksession.insert( "go2" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go2", list.get(2)); assertEquals( "not blah", list.get(3)); fh = ksession.insert( "go3" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go3", list.get(4)); assertEquals( "exists blah", list.get(5)); fh = ksession.insert( "go4" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go4", list.get(6)); assertEquals( "not blah", list.get(7)); fh = ksession.insert( "go5" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go5", list.get(8)); assertEquals( "exists blah", list.get(9)); // This simulates a modify of the root DroolsQuery object, but first we break it fh = ksession.insert( "go6" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go6", list.get(10)); assertEquals( "not blah", list.get(11)); // now fix it fh = ksession.insert( "go7" ); ksession.fireAllRules(); ksession.retract( fh ); assertEquals( "go7", list.get(12)); assertEquals( "exists blah", list.get(13)); System.out.println( list );