To understand their function, one must look at the structural sources of their "intelligence":
Expert Systems are a specific subset of AI designed to emulate the decision-making ability of a human expert in a narrow field. Artificial Intelligence & Expert Systems Source...
The "brain" that applies logical rules to the knowledge base to reach a result. To understand their function, one must look at
The mechanism that allows non-experts to query the system and receive understandable advice. Real-World Applications To understand their function