Very nice article. We should all know these rules, but more importantly the database vendors should keep them in mind whenever they build something.

Here is a paper that discusses in more detail the Codd's twelve rules and how "the big three" DBMS-s are following them:

http://www.handels.gu.se/epc/archive/00002948/01/Nr18_MIB.pdf

All my respects to the late Mr. Codd; here are some things about his life and his work:

http://www.bayarea.com/mld/mercurynews/news/5676110.htm

Razvan