Bug 177504 Engine doesn't provide SubQuery for extended item
Engine doesn't provide SubQuery for extended item, so chart can't use container's binding to execute the query. If possible, engine could provide an option for extended item to choose whether engine could create the query, so extended item won't create SubQuery by itself.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
/**
	 * link the query and report item
	 * @param query
	 * @param reportItem
	 */
	private void registerQueryAndElement( IDataQueryDefinition query,
			ReportItemDesign reportItem )
	{
		assert query != null && reportItem != null;
		HashMap map = report.getReportItemToQueryMap( );
		assert map != null;
		map.put( query, reportItem );
	}
	
	/**
	 * register the query to handle
	 * @param handle
	 * @param query
	 */
	private void registerQueryToHandle( ReportItemDesign reportItem, IDataQueryDefinition[] queries )
	{
		DesignElementHandle handle = reportItem.getHandle( );
		assert handle instanceof ReportElementHandle;
		report.setQueryToReportHandle( (ReportElementHandle)handle, queries );
	}
	/**
	 * The visitor class that actually builds the report query
	 */
	protected class QueryBuilderVisitor extends DefaultReportItemVisitorImpl