MYCIN is one of the most famous Expert Systems that triggered the second AI booming in 1980s. The new concepts such as ‘knowledge-based’, ‘knowledge-engineering’, ‘knowledge-acquisition’ were supported by what is called ‘rule-based system’ or ‘production system’, which is based on a collection of ‘IF ~ THEN ~’ forms. In the rule-based systems, one can see that ‘knowledge’ represented by rules is parted from procedures of program or reasoning engine, and such architecture allows the flexible and incremental development of problem-solving systems.
Historically, MYCIN is the first system that introduced the uncertainty on knowledge description and reasoning decision. It comes from the ‘heuristic knowledge’ of human experts.
For the purpose of the direction to reasoning and the instantiation of subjective thing, MYCIN introduced what is called ‘context tree’. At the initial stage, the context tree represents a scenario of reasoning, and the system proceeds according to the scenario. In the process, MYCIN establishes the instance of subjective things, such as PATIENT-1, CULTURE-1 and CULTURE-2, and ORGANIZM-1, ORGANIZM-2, ORGANIZM-3. Thus, in MYCIN, reasoning process is the fixing process of subjective things, and fixed organisms are regarded as the causes of an infection disease.