Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402262032.24127ed9_at_posting.google.com...
> Unless Date was talking about a db with one two-column (one of which
> one is auto supplied) table, Date is wrong.

Read the chapter again. He wasn't talking about one 2-column "table", and yet he's still not wrong. Read what he did say.

> Only the one in Date's books on pg 123 of his 6th Ed.
> "Codd now regards nulls as an integral part of the relational model"

He's talking about Codd's opinion, not his own. The rest of his chapter on missing information explains his opinion clearly.

> Date's Intro to Dbs, 6th Ed, pg 570, 1st paragrah of Chapter 20 -
> Missing Info: "the problem of missing information is one that is
> encountered very frequently in the real world", "are too common in
> real-world situations and so it is necessary to have some way of
> dealing with such situations in our formal database system".

That doesn't say anything about nulls. It talks about Missing Information. He explains the difference extremely clearly.

> Chapter
> Summary: "3VL suffers from the very serious ("showstopper") problem
> that it does not match reality, that is results that are correct
> according to 3VL are sometimes incorrect in the real world".

Yes, he's right about that. You're incorrect in assuming that nulls arise from RDM naturally. Codd said that (sort of), and Date refuted it. Received on Fri Feb 27 2004 - 22:07:52 CET