1. An automated method for supporting a clinical diagnosis for a patient, comprising: receiving, by a processor, patient-specific information regarding a plurality of symptoms associated with one or more of a plurality of diseases, wherein the patient-specific information regarding the plurality of symptoms categorizes each of a first subset of the plurality of symptoms as a present symptom determined as being present in the patient, and categorizes each of a second subset of the plurality of symptoms as an absent symptom determined as being absent in the patient; storing in memory the patient-specific information regarding the plurality of symptoms associated with the patient; the processor establishing or accessing a multi-tier relationship between said plurality of symptoms and the plurality of diseases defining, for each disease, one or more of the plurality of symptoms that match that disease; the processor adjusting at least one weighting factor for at least one (a) at least one of said multi-tier relationships and (b) at least one of said symptoms, based on a knowledge model; and the processor building a ranking of diseases from said multi-tier relationship based on said weighting factors and said patient-specific information regarding the plurality of symptoms; wherein for each respective disease, the number of symptoms categorized as present symptoms for the patient that match the respective disease, as defined by the multi-tier relationship, increases the ranking of the respective disease; and wherein the number of symptoms categorized as absent symptoms for the patient that match the respective disease, as defined by the multi-tier relationship, decreases the ranking of the respective disease.
4. The method of claim 1 , wherein the received patient-specific information regarding the plurality of symptoms categorizes each of a third subset of the plurality of symptoms as an open system not determined as being present or absent in the patient.