An expert system is a computer program that uses artificial intelligence (AI) technologies to simulate the judgment and behavior of a human or an organization that has expertise and experience in a particular field. It is designed to solve complex problems by reasoning through bodies of knowledge, represented mainly as if-then rules rather than through conventional procedural code. The first expert systems were created in the 1970s and proliferated in the 1980s. Expert systems are divided into two subsystems: the inference engine and the knowledge base. The knowledge base represents facts and rules, while the inference engine maps known information from the knowledge base to a set of rules and makes decisions based on those inputs.

Expert systems are usually intended to complement, not replace, human experts. They can advise users as well as provide explanations to them about how they reached a particular conclusion or advice. Expert systems can be effective in specific domains or subject areas where experts are required to make diagnoses, judgments, or predictions. They have played a large role in many industries, including law, medical diagnosis, accounting, coding, games, and more.

Components of an expert system include the knowledge base, inference engine, user interface, explanation facility, and knowledge acquisition facility. The knowledge base is where the information is stored, created from information provided by human experts. The inference engine acts like a search engine, examining the knowledge base for information that matches the user’s query/search. The user interface is the part of the expert system that end-users interact with to get an answer to their question or problem. The explanation facility describes how the problem was solved, while the knowledge acquisition facility is used to add new knowledge to the knowledge base.

Expert systems have several advantages, including increased availability and reliability, multiple expertise, explanation, and fast response. They can be accessed on any computer hardware and the system always completes responses on time. Several expert systems can be run simultaneously to solve a problem and gain a higher level of expertise than a human expert. Expert systems always describe how the problem was solved, and they provide fast responses.