Editing Knowledge-based systems (section)

===Rule-based systems===
{{main|Rule-based system}}
The first knowledge-based systems were primarily rule-based expert systems. These represented facts about the world as simple assertions in a flat [[database]] and used domain-specific rules to reason about these assertions, and then to add to them. One of the most famous of these early systems was [[Mycin]], a program for medical diagnosis. 

Representing knowledge explicitly via rules had several advantages:
# ''Acquisition and maintenance.'' Using rules meant that domain experts could often define and maintain the rules themselves rather than via a programmer.
# ''Explanation.'' Representing knowledge explicitly allowed systems to reason about how they came to a conclusion and use this information to explain results to users. For example, to follow the chain of inferences that led to a diagnosis and use these facts to explain the diagnosis. 
# ''Reasoning.'' Decoupling the knowledge from the processing of that knowledge enabled general purpose inference engines to be developed. These systems could develop conclusions that followed from a data set that the initial developers may not have even been aware of.<ref>{{Cite book |last=Hayes-Roth |first=Frederick |url=https://archive.org/details/buildingexpertsy00temd |title=Building Expert Systems |last2=Donald Waterman |last3=Douglas Lenat |publisher=Addison-Wesley |year=1983 |isbn=0-201-10686-8}}</ref>