Warning - the bibtex entry below may be invalid: 
Missing 'journal' field 
@article{hmpuISWC2009,
  address = "Chantilly, VA, USA.",
  author = "H\'ector P\'erez-Urbina and Ian Horrocks and Boris Motik",
  booktitle = "In Proc.\ of the Int.\ Semantic Web Conference (ISWC2009)",
  month = "October",
  note = "to appear",
  title = "{Efficient Query Answering for OWL 2}",
  year = "2009",
}