Si riporta qui di seguito la definizione dei termini "sistema esperto" e "motore inferenziale" fornita dall'enciclopedia Microsoft Encarta (Copyright 1994 Microsoft Corporation. Copyright 1994 Funk & Wagnall's Corporation) : "Expert System, a type of computer application program that makes decisions or solves problems in a particular field, such as finance or medicine, by using knowledge and analytical rules defined by experts in the field. Human experts solve problems by using a combination of factual knowledge and reasoning ability. In an expert system, these two essentials are contained in two separate but related components, a knowledge base and an inference engine. The knowledge base provides specific facts and rules about the subject, and the inference engine provides the reasoning ability that enables the expert system to form conclusions (...). Expert systems originated in the 1960s; fields in which they are used include chemistry, geology, medicine, banking and investments, and insurance".