A system, method, and computer program for editing a production schedule. The system includes: a storage unit storing master data; a receiving unit receiving the master data; a duplicating unit generating editing data; an editing operation unit generating preliminarily-edited data based on an editing command; an identification unit identifying an item edited in the preliminarily-edited data with respect to the master data; a determination unit determining whether the inputted editing command is valid or invalid, wherein tag information is appended to an item being the same as the edited item; and an updating unit generating the preliminarily-edited data in which the editing command determined to be valid is reflected and to which the tag information is appended and updating the master data by using the generated preliminarily-edited data. A method and computer program are also provided.