What is an example of an expert system?

One example of an expert system is an artificial intelligence system that emulates an auto mechanic's knowledge in diagnosing automobile problems. This hypothetical expert system would likely be the result of engineering using an actual mechanic's knowledge base.

Expert systems are designed by knowledgeable engineers to simulate the type of reasoning, decision-making and cognitive processes that an expert in a given field or occupation would demonstrate. There are two primary parts to expert systems – a knowledge base and a reasoning engine. The knowledge base contains both factual and judgemental knowledge. The reasoning engine uses inference to solve problems, often using "if-then" decision chains.