@inproceedings{ICALP-1981-Ullman,
	author        = "Jeffrey D. Ullman",
	booktitle     = "{Proceedings of the Eighth Colloquium on Automata, Languages and Programming}",
	doi           = "10.1007/3-540-10843-2_13",
	isbn          = "3-540-10843-2",
	pages         = "165--176",
	publisher     = "{Springer-Verlag}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{A View of Directions in Relational Database Theory}",
	volume        = 115,
	year          = 1981,
}