@book{DBLP:books/cs/Ullman88,
  author    = {Jeffrey D. Ullman},
  title     = {Principles of Database  and Knowledge-Base Systems, Volume
               I},
  publisher = {Computer Science Press},
  year      = {1988},
  isbn      = {0-7167-8158-1},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}