@article{OrPi11,
  title = "Optimizing Query Answering under Ontological Constraints",
  author = "Giorgio Orsi and Andreas Pieris",
  year = "2011",
  journal = "Proceedings of the VLDB Endowment (PVLDB)",
  month = "August",
  number = "11",
  pages = "1004--1015",
  url = "http://www.vldb.org/pvldb/vol4/p1004-orsi.pdf",
  volume = "4",
}