15. The system of claim 9 , wherein the program instructions further configure the ontology mediation engine to: mediate the one or more system ontologies, the one or more domain ontologies, and the data source ontologies to a central ontology in a star configuration.
9. A system comprising: a plurality of data sources; one or more computer processors; and one or more memories coupled to the one or more computer processors and storing program instructions executable by the one or more computer processors to implement an ontology mediation engine configured to: generate a data source schema for each data source; map each data source schema to one of a plurality of data source ontologies; map each data source ontology to one or more domain ontologies; map the one or more domain ontologies to one or more system ontologies; and, generate an interactive display for a graphical user interface on a client device, wherein the interactive display comprises a visual representation of relationships between attributes of an ontology, the ontology selected from the group comprising the one or more system ontologies, the one or more domain ontologies, and the data source ontologies, and wherein the visual representation further comprises one or more user selectable attributes of the ontology; receive, by the computer, a selection of the one or more attributes of the ontology made by a user; generate, by the computer, a query based on the selection, wherein the generated query corresponds to the ontology; translate, by the computer, the query into a plurality of translated queries, wherein each translated query corresponds to a respective one of the plurality of data source ontologies; execute each of the plurality of translated queries over a respective one of the plurality of data sources; translate, by the computer, one or more results sets into a unified result, wherein the unified result corresponds to the ontology; and display the unified result, wherein the unified result is associated with one or more of the data sources and wherein the unified result comprises a list of one or more user selectable documents.