### 3.3.2.1: Classification

Let *D* be a set of objects. A system of non empty, pair-wise
disjoint subsets *K*_{1},K_{2},...,K_{n} with *D=K*_{1}K_{2}...K_{n} , *K*_{i}K_{j}=Ø i,j{1,...,n}, ij is called a classification of *D* into
*
classes* *K*_{1},K_{2},...,K_{n} .

A sequence of such systems is called a
*
strongly hierarchical classification
system* if for each pair of a class from a system
and its successor the class of the successor system is either a subset
of its predecessor class or disjoint to it. This means that each class
is divided into subclasses in the successor system.

© 1998 / HTML-Version 17. 11. 1998: R. Ferber