[rules-users] Implementing Refraction with Drools

[magaram]

Thanks for the clarifications Mark and Wolfgang. I wanted to share some
additional data.
I was trying to reproduce the same behavior that ILOG JRules exhibits by
default for refraction.

My experiment with no-loop and lock-on-active did not work when I compared
against my baseline results with JRules. However, the interesting part was
when I ratified the agenda filter as follows (wrong and hacky as it is) -
removed the encounteredActivations.remove(act) before returning false, it
matched the ILOG baselines exactly. I ran through 46 test cases as part of
my baseline, all of which have several looping opportunities single and
complex. My earlier agenda filter implementation that I posted earlier did
not yield identical results with the JRules baseline.

It seems this logic for refraction seems to mimic JRules refraction
behavior.  From commercial use case perspective refraction/repeatability
control is important. ILOG implements refraction out of the box as part of
conflict resolution. However they offer up a antecedent directive called
refresh (in lieu of update) that overrides refraction...

import java.util.ArrayList;
import java.util.List;

import org.drools.runtime.rule.Activation;
import org.drools.runtime.rule.AgendaFilter;

/**
 * This custom agenda filter injects refraction behavior into the rule
engine
 * @author Mukundan Agaram
 *
 */
public class RefractionAgendaFilter implements AgendaFilter {
	private List<Activation> encounteredActivations = new
ArrayList<Activation>();

	@Override
	public boolean accept(Activation act) 
	{
		//Check for a Refraction
		if (encounteredActivations.contains(act))
		{
			return false;
		}
		//Otherwise add the rule to check for potential refractions in the future
		encounteredActivations.add(act);
		//select the rule to be part of the agenda
		return true;
	}

}




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