Attaching instance variables to method realization1 instead of classes

The authors discuss an object model in which instance-variable definitions are associated with the implementations of each method in a class, rather than with the class as a whole. This allows avoidance of recompilation of methods and invalidation of existing objects when new instance variables are introduced for a class, smooth integration of temporary objects with objects in persistent stores, freedom to optimize the physical database organization of instance variables without recompiling method implementations, exposure of a separate `view´ of an object to each of its methods, reuse of method implementations to obtain similar functions on different instance variables of an object and on objects of different classes with differently structured instance variables, and separate compilation of classes and method implementations