@ARTICLE {
	AUTHOR = "Jorge P{\'e}rez and Marcelo Arenas and Claudio Gutierrez",
	TITLE ="Semantics and complexity of SPARQL",
	JOURNAL = "Transactions on Database Systems (TODS)",
	VOLUME = "34",
	NUMBER = "3",
	YEAR = "2009",
	PUBLISHER = "ACM Press",
	ADDRESS = "New York, NY, USA",
	ISSN = "0362-5915"
	NOTE = "Article 16",
	}