The demand for true “system integration” leads to an increasing number of Application Specific Integrated Circuit (ASIC) designs having non-standard electrical and timing input/output characteristics and operating environments. This mandates a computer assistance during the specification phase as well as the management of intermediate and final design results. Furthermore, early and simulation independent consistency checking is necessary to prevent expensive redesigns. This paper presents a new knowledge based approach to the acquisition, checking and processing of electrical, timing, environmental and test oriented specification data using object-oriented data representation and rule-based consistency checking. This approach is part of the DEBYS (DEsign BY Specification) project under development at the University of Erlangen-Nuernberg. This system is currently working for digital ASIC and will be enhanced for system design.