The interest in MC_SC2 in the MCDA group was rather
weak, comparing to Multiple Criteria Choice and Ranking. In contemporary
decision practice it appears, however, that the Russell's saying is
true: "in fact all decision is a classification", or even more,
"knowledge is an ability of classification" [Roman Słowiński].
Groups can be defined a priori or a posteriori.
In the latter case, it is common to build a procedure based on a
similarity measure which assigns to the same group
(cluster), objects having identical characteristics
according to that measure. Groups are thus formed a
posteriori. In literature these procedures are known as
In the former case, groups (classes
or categories) are pre-defined by using limit profiles,
upper and lower bounds, central objects or other norms.
Based on these reference objects a
procedure is defined for assigning objects to the
When there is no preference relation
among the groups (classes) we refer to the nominal
classification (or discrimination) problem.
If the groups (categories) are
ordered from the worst to the best one, or vice-versa, the
problem is called an ordinal classification (or sorting or