[ Editor's Note: This is a guest article by Daniel Tunkelang. (See his bio below.) Daniel is passionate about designing search systems that improve users' experience with information retrieval. This passion comes across very strongly in his book about faceted search, which I recently ... [-->]
Hmm, i can imagine federated search over some sparql-endpoints even if i have no idea if it's possible to make it fast enough. But federation across ranked/set based fulltext search engines? IMHO rather impossible than difficult.
