Nonsubversion Rule:
There should be no way to modify the database structure other than through the multiple row database language (like SQL).
"Nonsubversion rule" is of not much significance in today's world. Most databases today support administrative tools that allow some direct manipulation of the datastructure.
Many people may find the DBA tools faster and easier than command language (SQL).
I think the Codd rules should be taken as guide lines and not standard.
But.. true.. it can be debated for hours without any conclusion !!

Sanjay