In this paper we present a conceptual data model, called S D M , which is able to represent the relationships between elementary and statistical data at a conceptual level. S D Mborrows elements from research both in Object Oriented Databases and in Knowledge Representation. In addition it has suitable mechanisms to form classes of individuals by classifying the instances of a target class according to some specied criteria. Notably, the class resulting from such a statistical aggregation can

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... en be t r eated exactly as a class of elementary data. This ability ful lls the often perceived necessity, in modeling real domains, of treating statistical aggregates and elementary data in an homogeneous way.