One of the most promising new knowledge representation methodologies is the "object-oriented" approach. One of the weak points in many of the object-oriented systems previously studied is the lack of a sufficiently efficient and powerful reasoning engine. For this reason, there has been a good deal of interest in developing a Prolog-based object-oriented programming system: Prolog has the most efficient and powerful reasoning technology available today. Quintus Computer Systems proposes to develop a sophisticated Object-Oriented Prolog System for modeling, simulation, and prototyping complex systems. This system will provide the best object-oriented tools in a Prolog environment, where the Prolog inference engine is available not just for reasoning but for the definition of methods to be associated with objects. Elegant and efficient access to foreign software will be added to provide the "multiple paradigm" environment that has been proven effective for fast modeling and prototyping of complex systems.The potential commercial application as described by the awardee: If the proposed emphasis on the use of Prolog compiler technology as the inferential component of an object-oriented system is as successful as preliminary investigations have suggested it will be, the potential commercial applications of the proposed research will range from the simulation of complex systems like logic designs to the control of operating systems to game playing.