The additional attributes you save in a subclass of [font=courier new]HomeXMLExporter[/font] should be read in a subclass of [font=courier new]HomeXMLHandler[/font].
But why don't you manage your additional information with the methods [font=courier new]setProperty[/font] / [font=courier new]getProperty[/font] available on subclasses of HomeObject, like the [font=courier new]Room[/font] class? This would prevent you from subclassing classes which handle XML files.