Abstract
Multi-level conceptual modeling addresses the representation of subject domains dealing with multiple classification levels. In such domains, the occurrence of situations in which instances of a type are specializations of another type is recurrent. This recurrent phenomenon is known in the conceptual modeling community as the powertype pattern. The relevance of the powertype pattern has led to its adoption in many important modeling initiatives, including the UML. To address the challenge of multi-level modeling, we have proposed an axiomatic well-founded theory called MLT. In this paper, we demonstrate how MLT can be used as a reference theory for capturing a number of nuances related to the modeling of the powertype pattern in conceptual modeling. Moreover, we show how this theory can be used to analyze, expose limitations and redesign the UML support for modeling this pattern.