@TechReport{BuchheitJeusfeldNuttStaudt93,
  author =    "Martin Buchheit and Manfred A. Jeusfeld and Werner Nutt and Martin Staudt",
  title =     "Subsumption between {Q}ueries to {O}bject-{O}riented {D}atabases",
  institution = "RWTH Aachen",
  year =      "1993",
  number =    "AIB-09-1993",
  url =       "http://aib.informatik.rwth-aachen.de/1993/1993-09.ps.gz",
}