In the same way as sorts and features are used in signatures to specify at the intensional level which MultiNet relations and functions can in principle describe certain relationships between conceptual representatives, a classification
of nodes is needed to achieve the analogue at the preextensional level. Thus, the element relation ELMT can hold only between an individual extensional which is not a set and a proper set, or between a set and a family of sets, and so on (see
the definition of the relation ELMT). Similarly, a subset relation can hold only between two sets of the same type (see the definition of the relation SUBM).

The attribute type of extensionality ( ETYPE ) is used whose values are summarily described in the following ([ETYPE=nil] characterizes concepts like intention, religiosity, etc., which
have no extension):

Means for Expressing Classification and Stratification

0 – Representative of an elementary extensional which is itself not a set.

   Examples: the extensionals of the house, Max, this school, . . .

1 – Set of elements of type 0

   Examples: the extensionals of several children, three cars, the crew, a family, . . .

2 – Set of elements of type 1

   Examples: the extensionals of three crews, many organizations, . . .

3 – Set of elements of type 2

   Example: the extensional of two umbrella organizations, where umbrella organization 
   is a concept already denoting a group of organizations (characterized by type 2).

In regard to cardinalities the corresponding attribute CARD is not applicable to extensionals of type 0. For an extensional E of type n, the cardinality is the number of the elements of E with type (n-1).