Implementations
Ingres, Obsolete, Quasi-relational Implementations, Required Technologies, Rules Engines, Third Manifesto
Model
12 Rules, A Relational Model of Data for Large Shared Data B, A Simple Guide to Five Normal Forms, According to Date: online., According to Date: recent., Against the Grain, Chracteristics of a Relational Database, Database Debunkings, Dilip's Brief Introduction to Relational Data, Dr EF "Ted" Codd's 12 Rules