@inproceedings{conf/dexa/GottlobLS99,
  title = "On Tractable Queries and Constraints",
  author = "Georg Gottlob and Nicola Leone and Francesco Scarcello",
  year = "1999",
  booktitle = "{Database and Expert Systems Applications, 10th International Conference, DEXA '99, Florence, Italy, August 30 - September
3, 1999, Proceedings}",
  editor = "Trevor J. M. Bench-Capon and Giovanni Soda and A. Min Tjoa",
  isbn = "3-540-66448-3",
  pages = "1-15",
  publisher = "Springer",
  series = "Lecture Notes in Computer Science",
  url = "http://link.springer.de/link/service/series/0558/bibs/1677/16770001.htm",
  volume = "1677",
}