1. A data management system, comprising: a storage medium that stores data in records, each record comprising a plurality of fields; and a controller that: receives an update file that contains: a stored data flag that indicates a presence or absence of updated data for each of the plurality of fields in a particular record, the updated data for each of the plurality of fields being disposed in a disposition sequence of the plurality of fields in the particular record; the updated data for the field that is to be updated; and an updated data flag that indicates the presence or absence of an update for each of the plurality of fields in the particular record; successively extracts the updated data from the update file in the disposition sequence; successively writes the corresponding extracted updated data into each of the fields for which the stored data flag indicates the presence of updated data in the disposition sequence; and erases the data in the field for which the stored data flag indicates the absence of updated data and for which the updated data flag indicates the presence of an update.