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
exp += IReportElementConstants.OUTER_BINDING_COLUMN_PREFIX;
		}
		exp += "[\"" + DEUtil.escape( column.getName( ) ) + "\"]";
		return exp;
	}
	/**
	 * Returns the level between the holder and the given handle
	 * 
	 * @param holder
	 *            the handle of the holder
	 * @param baseElement
	 *            the handle of the base element
	 * 
	 * @return the level between the holder and the base element, or -1 if the
	 *         element is not a children of the holder
	 */
	public static int getBindingLevel( DesignElementHandle holder,
			DesignElementHandle baseElement )
	{
		int level = 0;
		for ( DesignElementHandle elementHandle = baseElement; elementHandle.getContainer( ) != null; elementHandle = getBindingHolder( elementHandle ).getContainer( ), level++ )
		{
			if ( getBindingHolder( elementHandle ) == holder )
			{
				return level;
			}
		}
		return -1;
	}
}