public function evalutateSetOperation( core_kernel_classes_Resource $setOperator,  common_Collection $actualSet,  core_kernel_classes_ContainerCollection $newSet)
    {
        $returnValue = null;

        
    	if($setOperator->getUri() == RulesRdf::INSTANCE_OPERATOR_UNION) {
			$returnValue = $actualSet->union($newSet);
    	}
    	else if($setOperator->getUri() == RulesRdf::INSTANCE_OPERATOR_INTERSECT) {
    		$returnValue =  $actualSet->intersect($newSet);
    	}
    	else {
    		throw new common_Exception('unknow set operator');
		}
        

        return $returnValue;
    }