@article{journals/jacm/GottlobK04,
  title = "Monadic datalog and the expressive power of languages for Web information extraction",
  author = "Georg Gottlob and Christoph Koch",
  year = "2004",
  journal = "J. {ACM}",
  number = "1",
  pages = "74-113",
  volume = "51",
  doi = "10.1145/962446.962450",
}