The Artificial Intelligence community sought to understand human intelligence by building computer programs, which exhibited intelligent behavior. Intelligence was perceived to be a problem solving ability. Most human problems appeared to have reasoned, rather than mathematical, solutions. The diagnosis of a disease could hardly be calculated. If a patient had a group of symptoms, then she had a particular disease. But, such reasoning required prior knowledge. The programs needed to have the knowledge that the disease exhibited a particular group of symptoms. For the AI community, that vague knowledge residing in the minds of Experts was superior to text book knowledge. So they called the programs, which solved such problems, Expert Systems.
Expert Systems managed goal oriented problem solving tasks including diagnosis, planning, scheduling, configuration and design. One method of knowledge representation was through If, then… rules. When the If part of a rule was satisfied, then the Then part of the rule was concluded. These became rule based Expert Systems. But knowledge was sometimes factual and at other times, vague. Factual knowledge had clear cause to effect...