In the area of artificial intelligence known as "expert systems," a knowledge base is constructed from expert knowledge about a topic. The topic is usually subject matter that aids decision making. So for instance a group of physicians possess knowledge about diagnostic decision making. They pool their knowledge and create the logic or rules on how they make diagnostic decisions. The inference engine uses the knowledge in the knowledge base to emulate that decision making using rules and inferences derived from those rules; and creating reliable outcomes from the process.