Roles and Dynamic Subclasses: a modal logic approach

In this paper, we argue that object-oriented models must be able to represent three kinds of taxonomic structures: static subclasses, dynamic subclasses and role classes. If CAR is a static subclass of VEHICLE, then a vehicle that is not a car can never migrate to the CAR subclass. If EMPloyee is a dynamic subclass of PERSON, then a PERSON that is not an employee may migrate to EMP. In both cases, an instance of the subclass is identical to an instance of the superclass. Finally, if EMP is modeled as a role class of PERSON every employee differs from every person, but a PERSON instance can acquire one or more EMP instances as roles. We outline an approach to formalizing these taxonomic structures in order-sorted dynamic logic with equality.