1. A computer-implemented method of ontology mediation, the method comprising: accessing, by a computer, a plurality of data sources; generating, by a computer, a data source schema for each data source; mapping, by the computer, each data source schema to one of a plurality of data source ontologies; mapping, by the computer, each data source ontology to one or more domain ontologies; mapping, by the computer, the one or more domain ontologies to one or more system ontologies; and generating, by the computer, 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; receiving, by the computer, a selection of the one or more attributes of the ontology made by a user; generating, by the computer, a query based on the selection, wherein the generated query corresponds to the ontology; translating, 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; executing each of the plurality of translated queries over a respective one of the plurality of data sources; translating, by the computer, one or more result sets into a unified result, wherein the unified result corresponds to the ontology; and displaying, by the computer, 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.