@inproceedings{PODS-2008-LibkinS,
	author        = "Leonid Libkin and Cristina Sirangelo",
	booktitle     = "{Proceedings of the 27th Symposium on Principles of Database Systems}",
	doi           = "10.1145/1376916.1376937",
	isbn          = "978-1-60558-108-8",
	pages         = "139--148",
	publisher     = "{ACM}",
	title         = "{Data exchange and schema mappings in open and closed worlds}",
	year          = 2008,
}