Bug 136270 Group's data binding column can only be used by the group itself
If you add some data binding columns to a group, these columns can only be used by this group itself. It should has a way to make the child can use the parent group's data binding column.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
return SessionHandleAdapter.getInstance( )
				.getReportDesignHandle( )
				.getVisibleDataSources( );
	}
	/**
	 * Returns all available column bindings for the given element
	 * 
	 * @param handle
	 *            the handle of the element
	 * @return the list of all column bindings available.The list order is from
	 *         the top to the given element
	 */
	public static List getAllColumnBindingList( DesignElementHandle handle )
	{
		return getAllColumnBindingList( handle, true );
	}
	/**
	 * Returns all available column bindings for the given element.
	 * 
	 * @param handle
	 *            the handle of the element
	 * @param includeSelf
	 *            true if includes the element itself, or false only includes
	 *            bindings in the containers
	 * @return the list of all column bindings available.The list order is from
	 *         the top to the given element
	 */
	public static List getAllColumnBindingList( DesignElementHandle handle,
			boolean includeSelf )
	{