Re: So what's null then if it's not nothing?

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Thu, 8 Dec 2005 16:13:46 +0100
Message-ID: <MPG.1e026c032ecb235a989733_at_news.ntnu.no>


In article <1134049822.702505.277830_at_g43g2000cwa.googlegroups.com>, boston103_at_hotmail.com says...
>
> > I'll have to say that your scheme above seems to have all the flaws of
> > Date's 2VL "special values" approach, *plus* extra complexity. YMMV.
>
> It's not my schema but rather Codd's.

Not according to how I read the article we are arguing about.

> That's how the SQL handles NULL (whatever NULL is assumed to mean).

I am not convinced of that. Have you found the relevant passages in the standard?

> > I'd say that what they mean---the semantics---is defined to a great
> > extend by how their operators work.
>
> What truth values, as well as various markers (I use the word marker
> in Codd's sense, not in Date's) represent is in the
> designer(s)/modeller(s) mind.

I meant NULLs generally, not truth values.

> > (And using numerals for both integers and floats is not the same thing.
> > Tell me if you're interested. :)
>
> It's not entirely the same sure, due to the prominent role logic plays
> in reasoning, but if one looks at the integers, rationals, 3VLs as
> just algebraic structures with different rules of the game, the
> analogy should be obvious.

No, I think the way you used it was a bad analogy. From memory, you compared the use of NULL as (for example) zero for integers and as UNKNOWN for 3VL truth values with the use of 3 as integer and as rational. But the number 3 is the same value, the same concept, regardless of the declared type of the variable holding it. Integer is a subdomain of rational. Besides, '3' alone in programming languages typically signifies the integer; '3d' or '3f' are expressions of the same number in floating-point types. You can assign '3' to a FP variable, but that is because of implicit type conversion, not because the same symbol denotes both an integer and a FP number. (Of course, I'm assuming a strongly typed language.) None of this is analogous to the NULL question.

-- 
Jon
Received on Thu Dec 08 2005 - 16:13:46 CET

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