@inproceedings{PODS-1991-HelmMO,
	author        = "Richard Helm and Kim Marriott and Martin Odersky",
	booktitle     = "{Proceedings of the 10th Symposium on Principles of Database Systems}",
	cdrom         = "['journals/anthology/cd1-3:PODS91/P181.PDF', 'journals/anthology/dvd1:text/1-3/PODS91/P181.PDF']",
	doi           = "10.1145/113413.113429",
	isbn          = "0-89791-430-9",
	pages         = "181--191",
	publisher     = "{ACM Press}",
	title         = "{Constraint-Based Query Optimization for Spatial Databases}",
	year          = 1991,
}