@inproceedings{LICS-1991-AvronH,
	author        = "Arnon Avron and Yoram Hirshfeld",
	booktitle     = "{Proceedings of the Sixth Annual Symposium on Logic in Computer Science}",
	doi           = "10.1109/LICS.1991.151647",
	isbn          = "0-8186-2230-X",
	pages         = "226--231",
	publisher     = "{IEEE Computer Society}",
	title         = "{On First Order Database Query Languages}",
	year          = 1991,
}