and in place of
hyperedges, there is a classification of relations. The set of entity
instances is called the universe of discourse, and the set of relation
instances is called the tuple space. In another sense, an IFF model is
a classification of hypergraphs &#8211; the instance aspect of a model forms
an instance hypergraph, and dually the type aspect of a model forms a
type language. IFF models are equivalent to the models of traditional
many-sorted logic. In this equivalence, the extent functions of the