@inproceedings{SIGMOD-1978-LeeG,
	author        = "R. M. Lee and Rob Gerritsen",
	booktitle     = "{Proceedings of the Eighth ACM SIGMOD International Conference on Management of Data}",
	cdrom         = "SIGMOD78/P018.PDF",
	doi           = "10.1145/509252.509263",
	pages         = "18--25",
	publisher     = "{ACM}",
	title         = "{Extended Semantics for Generalization Hierarchies}",
	year          = 1978,
}