Codd and non-simple domains

I am pretty naive when it comes to DB theory but there is something I am trying to find out and having no luck. In Codd's 70's paper on the relational database, he explains normalization as a process of taking non-simple domains out and create separate relations where the primary key is expanded with the parent relations key. He assumes that such non-simple domains occur in a tree format. He specifically states:

"If normalization as described above is to be applicable, the unnormalized collection of relations must satisfy the following conditions :
(1) The graph of interrelationships of the nonsimple
domains is a collection of trees.
(2) No primary key has a component domain which is
nonsimple.
The writer knows of no application which would require any relaxation of these conditions. Further operations of a normalizing kind are possible. These are not discussed in this paper."

My question is is this true for modern RDBs? Essentially, if the graph is a tree, then there would always be a single path between two tables in terms of key inclusion in the primary key of child tables. Is this safe to assume to be true for any set of tables in 3NF or even 1NF?

Thanks in advance for any help.

Cheers,
Dev Received on Wed Aug 31 2005 - 15:01:32 CEST