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 field specifying structure that specifies a field that is to be updated in a particular record and that contains the updated data for the field that is to be updated; and writes, for the particular record, the updated data that has been extracted from the update file into the field that has been specified by the stored field specifying structure of the update file.