A large knowledge-based system.
Cyc is a very large, multi-contextual knowledge base and inference engine, the development of which started at the Microelectronics and Computer Technology Corporation (MCC) in Austin, Texas during the early 1980s.
Over the past eleven years the members of the Cyc team, lead by Doug Lenat, have added to the knowledge base a huge amount of fundamental human knowledge: facts, rules of thumb, and heuristics for reasoning about the objects and events of modern everyday life.
Cyc is an attempt to do symbolic AI on a massive scale. It is not based on numerical methods such as statistical probabilities, nor is it based on neural networks or fuzzy logic. All of the knowledge in Cyc is represented declaratively in the form of logical assertions. Cyc presently contains approximately 400,000 significant assertions, which include simple statements of fact, rules about what conclusions to draw if certain statements of fact are satisfied, and rules about how to reason with certain types of facts and rules. The inference engine derives new conclusions using deductive reasoning.