Interoperability of programming languages with persistency requires new concepts to make a single knowledge base management system (KBMS), a custom-tailored tool for applications of various programming languages and of different programming paradigms. The authors describe a method for the horizontal integration of KBMS applications from different programming languages. They used the commonly known ADT definition technique to maintain a vertical integration between languages and the KBMS, and propose schema sharing and polymorphism as the background for this particular kind of interoperability. The suggested approach was validated by an extended KBMS object manager, the conceptual object manager. Some of the design principles of the conceptual object manager, the vertical integration task, and the semantics of the horizontal integration are considered.>