public Node getNode(String idRef) throws IDrefNotInSentenceException {
		if (terminals.containsKey(idRef))
			return terminals.get(idRef);
		else if (nonterminals.containsKey(idRef))
			return nonterminals.get(idRef);
		else throw new IDrefNotInSentenceException("idRef: " + idRef + " not in Sentence: " + getId());
	}