The SOMobjects Developer Toolkit provides
The SOM run-time library provides a set of functions used primarily for creating objects and invoking methods on them. The data structures and objects that are created, maintained, and used by the functions in the SOM run-time library constitute the SOM run-time environment.
A distinguishing characteristic of the SOM run-time environment is that SOM classes are represented by run-time objects; these objects are called class objects. By contrast, other object-oriented languages such as C++ treat classes strictly as compile-time structures that have no properties at run time. In SOM, however, each class has a corresponding run-time object. This has three advantages: First, application programs can access information about a class at run time, including its relationships with other classes, the methods it supports, the size of its instances, and so on. Second, because much of the information about a class is established at run time rather than at compile time, application programs needn't be recompiled when this information changes. Finally, because class objects can be instances of user-defined classes in SOM, users can adapt the techniques for subclassing and inheritance in order to build object-oriented solutions to problems that are otherwise not easily addressed within an OOP context.