[rules-dev] Truth Maintenance over Directed Graphs using Reactive Derivation Queries

[Mark Proctor]

      http://blog.athico.com/2011/06/truth-maintenance-over-directed-graphs.html

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      Truth Maintenance over Directed Graphs using Reactive Derivation
      Queries
      <http://blog.athico.com/2011/06/truth-maintenance-over-directed-graphs.html>


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 );

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