@inproceedings{SPARQLiswc2014,
  title = "On the Semantics of SPARQL Queries with Optional Matching Under Entailment Regimes",
  author = "Egor V. Kostylev, Bernardo Cuenca Grau",
  year = "2014",
  booktitle = "Proceedings of the 13th International Semantic Web Conference (ISWC)",
}