@ARTICLE {
	AUTHOR = "Leonid Libkin and Antonella Poggi and Cristina Sirangelo and Pablo Barcel{\'o}",
	TITLE ="XML with Incomplete Information",
	JOURNAL = "Journal of the ACM (JACM)",
	VOLUME = "58",
	NUMBER = "1",
	PAGES = "article 4",
	MONTH = "Dec",
	YEAR = "2010",
	PUBLISHER = "ACM Press",
	ADDRESS = "New York, NY, USA",
	ISSN = "0004-5411"
	}