what is the differences between the pure relational data model and the usual implementation using SQL?

This looks like a homework question. Have you tried looking for an answer yourself? There are plenty of books that cover this topic.

This post is a duplicate with:
http://www.dbforums.com/other/165629...ata-model.html

Duplicate deleted.

It sounds like a novel idea Dave has - do your homework yourself rather than get other people do it for you. Maybe you would even learn something. Perhaps you should give it a go?

The pure relational model exists only in academia. The SQL implementation might actually exist.

-PatP

There are very close implementations of TRM. Here's one that's quite advanced, and my own work, which is still more documentation than usable code.

BTW, saw your kind words that you sent ages ago, thanks very much. One thing about being stuck out here, I've gotten a hell of a lot of work done on my little project.