For example, ontology mapping works if two disease ontologies are to be aligned. viagra generic For example, ontology linking is appropriate for aligning disease and symptom ontologies as diseases and symptoms are separate concepts. viagra generic A strict requirement is that the domains of the ontologies that are being combined are disjoint. viagra generic Special mapping constructs are used to indicate how elements from different ontologies are semantically related or equivalent. viagra generic In such case, disease classes from both ontologies are matched.