Knowledge-based systems (KBS) are one of the branches of artificial intelligence. (AI). KBS uses knowledge from human domain experts to facilitate the decision-making process. An example of KBS is expert systems. Among the methods used to reason a decision-making process in KBS are fuzzy logic, rule-based and case-based reasoning. The main components of KBS include user interface facilities, inference engine, and knowledge base. The application of KBS varies from legal, business, medical and other relevant domains.