public function getCompositionRules()
    {
        $subExpressions = array();
        foreach ($this->components as $irp) {
        	$subExpressions[] = new CommonExpression('variable', array('identifier' => $irp->getOutcome()->getIdentifier()));
        }
        $sum = new CommonExpression('sum', array());
        $sum->setSubExpressions($subExpressions);
        $summationRule = new SetOutcomeVariable($this->outcomeIdentifier, $sum);
        
        $returnValue = array($summationRule);

        return (array) $returnValue;
    }