Physician analogy for defect taxonomy

Consider a physician making a diagnosis for a patient. The patient enters the physician's office with a list of failures (that is, symptoms). The physician then must discover the fault, i.e., the root cause of the symptom. To aid in the diagnosis, he may order tests that look for anomalous internal conditions, such as high blood pressure, an irregular heartbeat, high levels of blood glucose, or high cholesterol. In our terminology, these anomalous internal conditions correspond to errors. <bib>ammann-offutt:2008</bib>