Characteristics of an expert system

• An expert system is built to perform at a human expert level in a narrow, specialized domain.
• Thus, the most important characteristics of an expert system is its high-quality performance. No matter how fast the system can solve a problem, the user will not be satisfied if the result is wrong. 
• On the other hand, the speed of reaching a solution is very important.
• Even the most accurate decision or diagnosis may not be useful if it is too late to apply, for instance, in an emergency, when a patient dies or a nuclear power plant explodes.
• Expert systems apply heuristics to guide the reasoning and thus reduce the search for a solution.
• A unique feature of an expert system is its explanation capability. It enables the expert system to review its own reasoning and explain its decision.
• Expert systems employ symbolic reasoning when solving a problem. Symbols are used to represent different types of knowledge such as facts, concepts and rules.