Three-level ontological model of abnormal states. This figure shows an example of the three levels of structural abnormality of our abnormality ontology. “Level 1” defines generic concepts, which are object-independent states, e.g., “small in area.” “Level 2” defines object-dependent abnormal states. States at the upper levels of Level 2 are dependent on generic structures, such as the “narrowing tube” and “narrowing valve,” which are common and are used in several domains. Note that concepts at the lower level of the tree are specialized into medicine-specific concepts such as vascular stenosis, arterial stenosis, and coronary artery stenosis. “Level 3” defines disease-dependent concepts. For example, “coronary artery stenosis in angina pectoris” is defined as a constituent of the disease “angina pectoris” at Layer 3.