Levels for Conceptual Modeling

Usually object types are organized in taxonomies by means of a specialization relation (also called subtyping or isa) 'implemented' by means of inheritance. This paper proposes a (non-incompatible) alternative to taxonomies that relies on three primitives: grounding, a specific kind of factual existential dependence, extensional atemporal parthood, and existence at a time. On the basis of these relations, specific, generic, and compositional grounding relations between object types are introduced. By clearly separating the objects from the substrata on which they are grounded, these grounding relations allow to stratify object types in levels and to manage inheritance in a flexible way. In particular, this approach helps to avoid isa overloading and to overcome some classical difficulties related to inheritance, e.g. attribute overriding, attribute hiding, or dynamic and multiple classification and specialization, that are relevant aspects especially in modeling roles.