1. A server system, comprising: a computer, including a computer readable medium and processor; a composite persistence unit, executing on the computer, wherein the composite persistence unit is comprised of a plurality of member persistence units each associated with one of a plurality of data sources; a first member persistence unit from the plurality of member persistence units, associated with a first data source; a second member persistence unit from the plurality of member persistence units, associated with a second data source; and an entity manager, created using the composite persistence unit, wherein when a request is received by the entity manager, the request is mapped to the appropriate member persistent unit and to its associated data source.