Abstract: A data integration system (100, 10-14) comprises a plurality of data sources (10-14) and a mapping system (120, 121, 122, 125, 126, 127, 128) for providing mapping between the data sources (10-14) and a global ontology. The global ontology comprises a plurality of elements including at least a plurality of concepts, at least some of which include one or more attributes. The data integration system further comprises a user interface (110). The user interface (110) is operable in use to provide an integrated, global view of the data contained in the data sources (10-14) and to permit a user to interact with the data sources (10-14) using the global ontology.