This paper presents a preliminary system structure supporting integration of expert systems and knowledge-based problem solving to other kinds of computing. The structure is based on layers on different abstraction levels communicating with each other through well-defined interface protocols. The result of applying such structure is a knowledge system capable of utilizing existing computer programs and information stores during its problem solving process. The structure is used in an application supporting hydrodynamic design of ships. A brief presentation of a demonstration system integrated to an existing ship design and engineering system is given.