1. A data management system, comprising: a storage device for hierarchically organizing and storing sets, or a collection of data that belong to a certain conditional scope, according to implications thereof; and a processing means for performing, when a set in the relatively upper level of the hierarchy is specified among the hierarchically structured sets stored in said storage device, a logical operation on all sets that belong to lower levels of the hierarchy thereof and for causing a predetermined display device to display a result of the logical operation as contents of said set specified.