Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402242236.68586a94_at_posting.google.com...
> Date is correct in that there is something inherently wrong with a
> model that allows NULLs.

Right.

> Codd is correct in that NULLs are an integral part of RDM.

No, he's not right, and Date showed that. Instead of just repeating "Chapter 20: Missing Information" in Date's book, can you actually show me a section or sentence or whatever that indicates that NULL is an integral part?

Codd invented relational. He stumbled in the implications of his ideas later. He was wrong. Date showed that in his book, in the same chapter you keep mentioning. What's not clear?

> When one substitutes "Not applicable" for NULL, the flaw is only
> partially masked. NULLs kill closure. How does substituting "Not
> applicable" for NULL significantly enhance closure?

NULLs mask far more: they mask meaning. Does NULL mean don't know, don't care, something-but-I-don't-know-what, etc?

You're right - my "NOT APPLICABLE" was a poor choice. The "no eyes" example, however, was a stretch. If the attribute truly isn't applicable, then you have the wrong predicate.

However, "UNKNOWN" is valid. It's a specific meaning, that NULL loses. It's useful in queries in many ways that NULL isn't. Received on Thu Feb 26 2004 - 19:19:31 CET