The process of restoring file integrity once a file has been found to be incorrect. There are two main classes of method. In a transaction processing system, in which a master file is updated incrementally, the method is based on backup copies and recovery logs. In a batch processing system, in which a master file is updated by being completely rewritten, the last version of the master file serves as the backup, and the transaction file serves as the recovery log. (The last version of the master file is then referred to as the father or parent, the version before that as the grandfather or grandparent, and so on.)