@misc{Kostylev2012:classification,
  title = "Classification of annotation semirings over query containment",
  author = "Egor V. Kostylev and Juan L. Reutter and Andr{\'a}s Z. Salamon",
  year = "2012",
  location = "Scottsdale, Arizona, USA",
  note = "Accepted to PODS 2012",
}