In this paper we introduce some logical and philosophical refinements
to OntoClean, first by developing some formal constraints on identity criteria, secondly
by specifying a kind of identity criteria, two level identity criteria, whose
role is to explain an identity among some entities referring to some other, more basic,
entities. Using such refinement we add a formal constraint to the stock of OntoClean
meta-constraints (OC+). We, then, observe that two level identity criteria
have an intuitive reading in terms of dependence of a kind of entities on some other
entities, possibly specified in terms of a grounding relation. Are identity criteria
grounding principles? In the second part of the paper we discuss this option
