@article {,
	title = {A Relational Model of Data for Large Shared Data Banks},
	journal = {Communications of the ACM},
	volume = {13},
	number = {6},
	year = {1970},
	pages = {377-387},
	keywords = {database normalization primary key relationship},
	url = {http://www.acm.org/classics/nov95/toc.html},
	author = {Codd, Edgar F.}
}