Expert systems are often used to solve problems in particular fields, such as in the medical or legal fields. For example, an expert system could receive information identifying the symptoms of a patient, analyze the symptoms, and identify possible diagnoses for the patient. A typical expert system includes a rulebase, or a set of rules, that embody the logic used by the expert system. A typical expert system also includes an inference engine. The inference engine typically executes the rules to analyze a set of inputs, such as the symptoms suffered by a patient. When executing the rules, the inference engine typically attempts to assign values to a set of output values. The output values represent the conclusions of the inference engine.