Hoist: A Second-Generation Expert System Based on Qualitative Physics

The system, Hoist, performs fault diagnosis without the use of a repair expert or shallow rules. Its knowledge is coded directly from a structural specification of the Mark 45 lower hoist. In a mechanism like the lower hoist, the functional model must reason about forces, fluid pressures, and mechanical linkages; that is, it must reason about qualitative physics. Hypothetical reasoning, the process embodied in Hoist, has general utility in qualitative physics and reason maintenance.