The main characteristic of endurants is that all of them are independent essential wholes.
A relation btw an instance of a concept and the name (instance of a concrete data type) of that concept. The name has to be a lexically meaningful name
Support for relations ranging on concrete data types
A relation btw an individual of a concept and the identifier of that concept. The identifier is a concrete data type, usually non-meaningful from the lexical viewpoint. Useful to map many database relationships