Bug 317267 [Automation][Regression]Error is thrown out when preview gantt type chart
chart/org.eclipse.birt.chart.engine.extension/src/org/eclipse/birt/chart/extension/datafeed/GanttDataSetProcessorImpl.java
throws ChartException
	{
		if ( ganttArray.length != 3 || ganttArray[0] == null )
		{
			throw new ChartException( ChartEngineExtensionPlugin.ID,
					ChartException.DATA_SET,
					"Invalid data set column" ); 
		}
		StringBuffer buffer = new StringBuffer( );
		buffer.append( "S" + String.valueOf( ganttArray[0] ) + " " ); 
		buffer.append( "E" + String.valueOf( ganttArray[1] ) + " " ); 
		buffer.append( String.valueOf( ganttArray[2] ) );
		return buffer;
	}
	
	/**
	 * return the array of indexes, the DataDefinitions with these id could be
	 * computed with aggregation function. By default, all the indexes will be
	 * added to the array. And this method should be overridden for some special
	 * chart types, such as bubble, stock...
	 * 
	 * @param series
	 * @return
	 */
	public int[] getDataDefIdsForGrouping( Series series )
	{
		return new int[]{0,1};
	}
	
}