Re: A question for Mr. Celko

John Jacob wrote:

>>EXACTLY!  This means that I can use characteristic functions on
>>columns, [...]

I don't know what John means. However, Rozhenstein developed some interesting SQL based on Sybase and what he called characteristic functions - functions which return 1 when a condition is true and 0 otherwise. You can Google on:

rozhenstein + characteristic + function

The first links lead to:

http://www.edbarlow.com/macros/macro_1.htm

There's also a reference to the out of print book on Amazon. I have a disintegrating copy on a bookshelf somewhere, and some worked examples for Informix databases on disk. I could make some of those available if there was interest enough.

> As for no recursion, self-references, and indeterminable sets, it
> sounds to me like this is just unnecessarily restricting the power of
> the language, a technique extremely common in today's systems, and one
> of the reasons relational languages get such a bad rap. Can you give a
> specific case where allowing relation-valued attributes would result
> in a wrong answer? Are you suggesting that allowing list, tuple, and
> relation-valued attributes somehow makes the language inconsistent
> (inconsistent in the formal sense meaning it would be possible to
> derive contradictory theorems)?

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
Guardian of DBD::Informix v2003.04 -- http://dbi.perl.org/