1. A system for creating a pretense of joining a plurality of type hierarchies in a single hierarchy, the system comprising a computer including a processor, a memory and input/output facilities, each type in each type hierarchy having a template describing objects that are instances of the type, comprising: at least one reference class to refer to the type hierarchies as if the referred type hierarchies were inherited from a common base class such that separate and unrelated ones of the type hierarchies can be joined together without modifying the type hierarchies, wherein the referred type hierarchies are not physically modified to refer to the common base class wherein the reference class further includes a discriminator which can refer to instances of at least one such type within one of the type hierarchies, wherein the discriminator discriminates between the type hierarchies; and for each type hierarchy, an initialization function which takes as an argument a reference to an instance of any of the types in the type hierarchy, wherein the initialization function is performed by loading the discriminator with the argument; and the initialization function is performed by loading the discriminator with the argument; and the processor being operative to read the reference class and responsive to the initialization function included for each type hierarchy to load the discriminator with the argument of the initialization function.