Hierarchical database

A hierarchical database, in which a lower class inherits to a property of an super class, having a class code for each class to identify the class, includes a first classification system having a regular class, and a second classification system having the regular class and a synonymous class referring to and using the regular class of the first classification system, wherein the synonymous class has an identification information to identify it is the synonymous class, a class code of the synonymous class, and a class code of the regular class of the first classification system to which the synonymous class refers.