@inproceedings{PODS-2002-ZhangTG,
	author        = "Donghui Zhang and Vassilis J. Tsotras and Dimitrios Gunopulos",
	booktitle     = "{Proceedings of the 21st Symposium on Principles of Database Systems}",
	doi           = "10.1145/543613.543629",
	ee            = "http://www.acm.org/sigs/sigmod/pods/proc02/papers/121-ZhangTG.pdf",
	isbn          = "1-58113-507-6",
	pages         = "121--132",
	publisher     = "{ACM}",
	title         = "{Efficient Aggregation over Objects with Extent}",
	year          = 2002,
}