  The purpose of this paper is to explore some semantic problems related to the
use of linguistic ontologies in information systems, and to suggest some
organizing principles aimed to solve such problems. The taxonomic structure of
current ontologies is unfortunately quite complicated and hard to understand,
especially for what concerns the upper levels. I will focus here on the problem
of ISA overloading, which I believe is the main responsible of these
difficulties. To this purpose, I will carefully analyze the ontological nature
of the categories used in current upper-level structures, considering the
necessity of splitting them according to more subtle distinctions or the
opportunity of excluding them because of their limited organizational role.
