related to many computer-aided technologies (CAx). There are two primary ways that KBE can be implemented: Build knowledge models from the ground up using knowledge-based technology Layer knowledge-based technology on top of existing CAD, simulation, and other engineering applications An early example of the first approach was the Simkit tool developed by Intellicorp in the 1980s. Simkit was developed on top of Intellicorp's Knowledge Engineering Environment (KEE). KEE was a very powerful knowledge-based systems development environment. KEE started on Lisp and added frames, objects, and rules, as well as powerful additional tools, such as hypothetical reasoning and truth maintenance. Simkit added stochastic simulation capabilities to the KEE environment. These capabilities included an event model, random distribution generators, simulation visualization, and more. The Simkit tool was an early example of KBE. It could define a simulation in terms of class models and rules and then run the simulation as a conventional simulation would. Along the way, the simulation could continue to invoke rules, demons, and object methods, providing the potential for much richer simulation as well as analysis than conventional simulation tools. One of the issues that Simkit faced was a common issue for most early KBE systems developed with this method: The Lisp knowledge-based environments provide very powerful knowledge representation and reasoning capabilities; however, they did so at the cost of massive requirements for memory and processing that stretched the limits of the computers of the time. Simkit could run simulations with thousands of objects and do very sophisticated analysis on those objects. However, industrial simulations often required tens or hundreds of thousands of objects, and Simkit had difficulty scaling up to such levels. The second alternative to developing KBE is illustrated by the CATIA product suite. CATIA started with products for CAD and other traditional industrial engineering applications and added knowledge-based capabilities on to them; for example, their KnowledgeWare module. History KBE developed in the 1980s. It was part of the initial wave of investment in Artificial Intelligence for business that fueled expert systems. Like expert systems, it relied on what at the time were leading edge advances in corporate information technology such as PCs, workstations, and client-server architectures. These same technologies were also facilitating the growth of CAx and CAD software. CAD tended to drive leading edge technologies and even push them past their current limits. The best example of this was object-oriented programming and database technology, which