ON “IDENTITIES” AND RELATIONAL FIDELITY

From: Alex Papadimoulis

Date: 4 Nov 2005

I found this quote to be amusing and thought you folks might appreciate it, too. This was in the context of a discussion on how using system-generated primary keys (IDENTITY) on each and every table was fundamentally wrong:

I have yet to see someone explain to me how using identities is NOT relational. Perhaps you can tell me without telling me to go read a book by Date.

--Ytram, thedailywtf.com/forums/

From: Fabian Pascal

RM requires every row to have at least one candidate key, but is mute on key choice, which is pragmatic, not theoretic. So using surrogate keys for every table as identifiers is not practical/advisable, but still within RM.

The problem is with OIDs, which are pointers, not values, which does violate the core Information Principle of the relational model.

Ed. Note: A PRACTICAL DATABASE FOUNDATION paper on keys is forthcoming.

Posted 1/27/2006