Logic-based Expert Systems :

Expert systems are agents that are programmed to make decisions just about real world situations are place together by utilising knowledge illicitation techniques to extract the information from human experts. Hence a particularly fruitful area is in opinion of diseases, when ever expert systems are need to decide (suggest) that disease a patient has, and given their symptoms.

Such expert systems are one of the major success stories of "AI". There Russell and Norvig give a very nice example from medicine like:
"A leading expert at lymph-node pathology describes a fiendishly complicated case to the expert system, examines the system's diagnosis. Now he scoffs at the system's response. Thus only slightly worried, about the creators of the system suggest he ask the computer for an explanation of the conclusion. There is the machine point out the major factors influencing its explanation and decision or the subtle interaction of several of the symptoms in this case. So after that the experts admits his error, ultimately."