Generally, physician will question the patient about chief complaint and other symptoms. He will diagnose body of patient, and he will send the patient to laboratory for careful diagnosis. However this research dose not considers the result from laboratory. So when we consider the process for diagnosis of physician, we will find 3 important components [3]. These components are problems of patient, data, and diagnosis. The diagnosis is an important condition for indicating accuracy. So design of inference engine of knowledge-based system must consider the process for diagnosis of physician, it is shown in figure 9. The inference engine of this knowledge-based system is interactive forward chaining (show in figure 10). It uses facts of symptom and indication of disease for definition direction of inference.