A data management system includes a processor. An estimated ETL level mapping processing unit is operated on the processor to estimate existence of unregistered ETL that is ETL not registered in a repository, to calculate a degree of similarity based on matching between an existing data model and retained data, and to extract a column to be a candidate based on the degree of similarity. The existence of the unregistered ETL is estimated by estimating the presence or absence of connectedness in the ETLs on the basis of correspondence between input data and output data in ETLs by using an execution ETL log relevant to an execution history of the ETL.