Creates the right data object for given primary file.
It is guaranteed that the provided file is realy primary file
returned from the method findPrimaryFile.
Parameters: primaryFile - the primary file the data object for this file exception: DataObjectExistsException - if the primary file already has data object
For a given file finds a primary file.
Parameters: fo - the file to find primary file for the primary file for the file or null if the file is notrecognized by this loader