An Educational System (ES) can be said to include several subsystems each of which serves a specific purpose. Educational systems may thus be subdivided into sections which are dedicated to the actual subject matter, the methods of teaching, the media, the students, the teachers, and to supporting organisations. The interrelations between such subsystems are presented in two-dimensional projects to the extent to which they are significant for Computer Assisted Instruction (CAI). The CAI-system and the dialogue languages must meet quality standards which permit the realisation of various teaching techniques and different methods of computer assistance. One such system exists in the "Stiftung Rehabilitation", a foundation at Heidelberg, Germany. The system uses APL and satisfies nearly all requirements which a CAI-system should meet. The realisation of this system is described herein.