An ontological information retrieval system is provided. According to an embodiment, the subject ontological information retrieval system can be utilized for computer-aided clinical Traditional Chinese Medicine (TCM) practice. In one implementation, a graphical user interface (GUI) is provided, enabling a user to input a query with symptoms determined from a patient, and the system's parser can find instances of the symptoms in a document object model (DOM) tree of the TCM ontological information. Diagnosis based upon the symptoms can be communicated to the user through the GUI. A relevance index (RI) and/or a frequency index (FI) can be further provided for evaluating a diagnosis by comparing the symptoms determined from a patient with the expected symptoms of the diagnosed illness and returning a value based on the number of matched symptoms, or a weighted index of matched symptoms.