PropertyHandle propHandle = getPropertyHandle( SimpleDataSet.COMPUTED_COLUMNS_PROP );
PropertyHandle propHandle = getPropertyHandle( IDataSetModel.COMPUTED_COLUMNS_PROP );
	public Iterator computedColumnsIterator( )	{		PropertyHandle propHandle = getPropertyHandle( SimpleDataSet.COMPUTED_COLUMNS_PROP );		assert propHandle != null;		return propHandle.iterator( );	}