905, A55, of the National Research Council for University Research. This distinction permits the incremental development of the so-called knowledge bases, in which the knowledge is stored, while the processing procedures remain unchanged and are usually reused for a wide range of applications. This possibility is crucial for the development of computer programs for problems which are usually solved by humans which posses a large amount of knowledge in problem s domain. The description of knowledge is much easier in an incremental process. It is easy to understand what knowledge has the system by reading the knowledge base.
Some environments offer the possibility of the integration of several paradigms.
Such an environment is XRL which has been used for the current system. The skeleton of this body is a taxonomy of the main concepts involved in that domain. These concepts have several attributes and relations connecting them with other concepts. Therefore, a frame-oriented knowledge representation is naturally suited for programs developed for supporting tutoring activities. For feeling the flavour of XRL, three objects are below exemplified.