Codd's paper is instructive from a historical perspective as well. When you read it, you realize that people were grappling with all these same issues before th

Codd's paper is instructive from a historical perspective as well. When you read it, you realize that people were grappling with all these same issues before the relational database came on the scene. His description of hierarchical data storage systems describes some of the issues with things like XML databases and XQuery pretty well.