It depends on the FileManager which performs the actual file reading and then signals that files have been added/removed.
The PlaceMarkManager keeps some information related to the data that it presents. It provides a MarblePlacemarkModel which presents the list of all placemarks of all files
The MarbleRunnerManager is a framework to query external servers for placemarks. The user types the query in the search line of the ControlBox widget, and then the MarbleRunnerManager triggers asynchronous runners which inherit from MarbleAbstractRunner.
The MarbleRunnerManager holds the resulting Placemarks until another query is input.