In semantic and object-oriented data models, each class has one or more typing properties that associate it to other classes, and carry type information about all instances of the class. We introduce a new kind of property that we call instance-typing property. An instance-typing property associates an instance of a class to another class, and carries Address for correspondence: Institute of Computer Science, Foundation for Research and Technology-Hellas, Iraklio, Greece y Research conducted while this author was visiting with the Institute of Computer Science, Foundation for Research and Technology-Hellas. Address for correspondence: Laboratoire de Recherche en Informatique, Universite de Paris-Sud, Orsay Cedex, France