public void add(Object o) throws PropertyException {
		if (o instanceof Event)
			addEvent((Event) o);
		else if (o instanceof Date)
			addDate((Date) o);
		else if (o instanceof Place)
			addPlace((Place) o);
		else
			throw new PropertyException("Unable to add object of type "
					+ o.getClass().getName() + " to an Attribute");
	}