The representation of knowledge may be accomplished by the development of rules, hierarchies, and through pattern matching. Estimating the value or utility of a treatment. This may be done by the system developer or by having patients estimate the value. Knowledge can be structured according to our world view. An example would be the following statement.
Hierarchies allow a compact and structured organization of knowledge.
An example would be symptoms and clinical findings from a patient compared to sets of symptoms and findings for diseases. The best match is considered the most likely diagnosis. The inference engine is the processing program in an expert system. It performs deductions or inference based on rules or facts. It is also capable of performing inexact reasoning based on probability or pattern matching.