[...] we require semantic uniqueness of properties: no two properties with the same semantics should be declared for two different domains, e.g. a property has age from people to number of years and a property life-span from animals to number of years should be merged and assigned to one appropriate domain (living beings), often introducing multiple inheritance. In practice, this principle turned out to be quite powerful to detect concepts of wide validity and to make the model stable under further extensions.

After a short time of development, we had evidence in 1996 for a set of base classes like: Temporal Entities, Actors, Physical Objects, Conceptual Objects, Place, Time, similar to Ranganathan’s Fundamental Categories, not so much from philosophical insight, but as appropriate domains for properties found in the source models.