The realisation that the problem domain for intelligent machines had to be
sufficiently restricted marked a major ‘paradigm shift’ in AI from generalpurpose,
knowledge-sparse, weak methods to domain-specific, knowledgeintensive
methods. This led to the development of expert systems – computer
programs capable of performing at a human-expert level in a narrow problem
area. Expert systems use human knowledge and expertise in the form of
specific rules, and are distinguished by the clean separation of the knowledge
and the reasoning mechanism. They can also explain their reasoning
procedures.