Anwering Recursive Queries under Keys and Foreign Keys is Undecidable.

Diego Calvanese Riccardo Rosati Anwering Recursive Queries under Keys and Foreign Keys is Undecidable. 2003 conf/krdb/2003 KRDB http://sunsite.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-79/calv-rosa-KRDB-2003.pdf db/conf/krdb/krdb2003.html#CalvaneseR03