Compute the document-id for a given file.
Parameters: publication - the publication where the file is. Parameters: area - the area where the file is. Parameters: file - the file that is associated with the document the document-id of the document associated with the given file. throws: DocumentDoesNotExistException - if there is no document associated with this file.
Returns the language for a given file
Parameters: file - the document file the language for the given document file or null if the filehas no language.