Matching Universal relation assumption Linked Data SPARQL References External links DB2 and Federated Databases Issues of where to perform the join aka "pushdown" and other performance characteristics Worked example federating Oracle, Informix, DB2, and Excel Freitas, André, Edward Curry, João Gabriel Oliveira, and Sean O’Riain. 2012. “Querying Heterogeneous Datasets on the Linked Data Web: Challenges, Approaches, and Trends.” IEEE Internet Computing 16 (1): 24–33. IBM Gaian Database: A dynamic Distributed Federated Database Federated system and methods and mechanisms of implementing and using such a system Database management systems