@inproceedings{VLDB-1991-Albert,
	author        = "Joseph Albert",
	booktitle     = "{Proceedings of the 17th International Conference on Very Large Data Bases}",
	ee            = "http://www.vldb.org/conf/1991/P211.PDF",
	isbn          = "1-55860-150-3",
	pages         = "211--219",
	publisher     = "{Morgan Kaufmann}",
	title         = "{Algebraic Properties of Bag Data Types}",
	year          = 1991,
}