Hierarchy as a new data type for qualitative variables

Qualitative variables take symbolic values such as cat, orange, California, Africa. Often these values can be arranged in levels of deeper detail. For example, the variable place_of_birth takes as level-1 values Africa, Asia... as level-2 values Nigeria, Japan... as level-3 values California, Massachusetts... These values are organized in a hierarchy H, a mathematical construct among these values. Over H, the following are defined: (1) the function confusion resulting when using a symbolic value instead of another; (2) the closeness to which object o fulfills predicate P; (3) a method which allows precision-controlled retrieval for relational databases whose objects have symbolic values.