Abstract
The Object Role Modeling language (ORM2) is one of the main conceptual modeling languages. Recently, a translation has been proposed of a main fragment of ORM2 (ORM2zero) into the description logic A£CQI, allowing the use of logical instruments in the analysis of ORM schemas. On the other hand, in many ontological domains there is a need for the formalization of defeasible information and of nonmonotonic forms of reasoning. Here we introduce two new constraints in ORM2 language, in order to formalize defeasible information into the schemas, and we explain how to translate such defeasible information in A£CQI.