General Formal Ontology (GFO)
The abstract top level (ATO) of GFO contains mainly two meta-categories:
set and item. Above the abstract top level there is a (non-formal)
level, which might be called philosophical level. On this level, several
distinct, philosophically basic assumptions are presented, mainly around the
notion of existence.
The abstract top level is used to express and model
the lower levels of GFO by set-theoretical expressions. To the abstract top
level two basic relations are associated: membership () and identity
(). The abstract top level of GFO is represented by a weak fragment
of set theory, and some weak axioms connecting sets with items.
Among the axioms concerning sets belong the following:
We may constrain the expressive power of the abstract top level by
stipulating that , are the only binary relations that are admitted in
the formulas of the ontology.