Abstract
In several subject domains, the categorization scheme itself is part of the subject matter. In this case, experts make use of categories of categories in their accounts. This has led to a number of approaches in conceptual modeling and knowledge representation that are called multi-level modeling approaches. An early approach for multi-level modeling is the powertype pattern which introduces "power types" and "base types". More recently, other proposals for multilevel modeling include "clabjects", "m-objects", which admit the existence of entities being somehow, simultaneously, types (classes) and instances (usually associated to objects). Regardless of the choice of approach to perform multi- level modelling, a question remains concerning the ontological status of "base types", "power types" and "clabjects". This paper aims to address this question through an ontological analysis. We use here the general term powertype to generally refer to types whose instances exhibit somehow both type-like and instance-like characteristics. We examine alternative accounts for powertype instances: (i) powertype instances as universals (abstract repeatable entities), (ii) powertype instances as mereological sums of instances of an associated type and (iii) powertype instances as variable embodiments. We conclude that the latter is the most promising account for an ontological interpretation of this phenomenon that meets the modelling desiderata for powertypes present in the literature.