TRULY RELATIONAL: What It Really Means (PRACTICAL DATABASE FOUNDATIONS Book 5)

In the first paragraph of his first published exposition of the relational data model (RDM) for database management in 1969, E.F. Codd claimed three core advantages:

· A dual sound theoretical foundation: first-order predicate logic (FOPL) and set theory;
· Physical data independence (PDI);
· DBMS-guaranteed data integrity and provably logically correct query results with respect to the real world.

Yet from 1969 to date the industry has failed to implement Codd’s ideas truly and fully. The closest it came to the RDM are SQL-based DBMS's that have only limited relational fidelity and violate the model in multiple ways. Moreover, instead of correcting mistakes, vendors—including IBM, where the RDM was invented and Oracle, the first implementer of a SQL DBMS—have regressed to the very costly and unproductive approaches that Codd’s innovation made obsolete forty-five years ago.

This paper revisits Codd’s ideas in his seminal first two papers, one being an important public revision of the other (an internal IBM document), containing changes and new material. It
· reasserts those aspects that have been ignored;
· recalls those that were missed;
· clarifies those that are opaque;
· corrects misinterpretations as well as original mistakes;
· settles some current disagreements on and confusion over what the RDM really is.


Table of Contents

Introduction
1. Relations on Domains
2. Relation Representation
3. Time-Varying Relations
4. Relation Interpretation
5. Data Sublanguage
6. Atomicity, Nested Relations, and Normalization
6. Foreign Keys and (First) Normal Form
7. Operations on Relations
8. Kinds of Relations
9. Derivability, Redundancy, Consistency
Conclusion

Appendix A: Codd’s 1969 Relational Operators
Appendix B: What's Wrong with These Pictures?