To date, knowledge-based systems (KBS's) have been developed on an ad-hoc basis, without the benefit of quantitative tools for analysis and synthesis. If we are to approach the field of knowledge engineering systematically, we must develop performance measures to characterize the effectiveness and efficiency of knowledge systems, and thereby serve to highlight directions for improvement. When KBS's are applied to control tasks, real-time performance becomes critical. Consequently, the internal processes of knowledge-based control systems (KBCS) must be optimized to fulfill real-time requirements. This article derives relationships between information attributes and system performance. The performance measures are applied to a knowledge-based design system (KBDS) for the synthesis of KBCS. The performance measures reflect intuitively satisfying properties of the KBDS and provide insights into the system not possible through a straight-forward inspection of the program code. This type of system can be used as a foundation for a high-level design environment. The performance measures, in conjunction with graphic interfaces, can enhance the productivity of control system design, increasing effectiveness while reducing development costs.