According to Date: online.
Articles by Christopher J Date about how the relational model can fulfill all OO needs. Web-only articles from DBPD that never made to print.
According to Date: recent.
Articles by Christohper J Date with emphasis on foundations. Web published by DBPD after the print magazine folded.
Database Debunkings
Analysis of various systems and ideas floating in the database scene, against the standards set by the relational model for database management.
Dr EF "Ted" Codd's 12 Rules
12 rules for a relational database management system, by the relational model's author. Outdated but still useful.
FirstSQL Issue Papers
Opinions fundamented on the relational model about NULLs, SQL and DBMS
The Third Manifesto
This is a proposal for a strictly relational system. It is intended to be more powerful than SQL or object DBMSs. File in PostScript format.