A database system that issues a reference transaction by designating a time stamp. Data structures are provided for making an inquiry about the latest value at a designated time using a database in which values and information on times associated with the individual values are contained in a table. One of the data structures includes, for each of IDs associated with the values in the database, at least one time stamp that is sorted in chronological order (hereinafter referred to as a first time stamp); values belonging to the individual first time stamps; and a pointer that designates one of the first time stamps, the first time stamps indicating the times when the values become valid. The other of the data structures includes, for each of the IDs, the designated first time stamp and a value belonging to the designated first time stamp.