Derivability, Redundancy and Consistency of Relations Stored in Large Data Banks "The first part of this paper is concerned with an explana-tion of a relational view of data. This view (or model) of data appears to be superior in several respects to the graph or network model [l, 2] presently in vogue. It provides a means of describing data with its natural structure only: that is, without superimposing any additional structure for machine representation purposes."
And the easier to find "A Relational Model of Data for Large Shared Data Banks". From, E. F. Codd.