Re: Does Codd's view of a relational database differ from that ofDate & Darwin? [M.Gittens]

Jan Hidders schrieb:
> mountain man wrote:
>

>>
>> There have been, there are,
>> and there always will be
>> NULLS in the real world.

Everything can be considered reality and everything can be considered abstraction - it is too general issue just like existence.

Nulls are equivalent of empty set (absence, hole etc.) and I can imagine a model without any other elements but not without nulls. In other words, null is what any model starts from and after that we can add any other non-primitive elements we want to see :-) Those other elements may pollute the model or may be argued to be unnecessary but not null values. Since nulls play such a role they are actually not true "values"( in the sense we use "normal" values, say, 5, 10 or "some text").

>> Does this fact not conflict
>> with Date's wants, and if
>> so, why does Date want
>> to ignore them?

Nothing can be modelled without null values. Null is a bootstrapping point for everything else. It is clear in theory, for example, in set theory. But it is also true in practice. Null values have very concrete semantics but the problem is that they are frequently used inappropriately (for example, as unknown values).

-- 
alex
http://conceptoriented.com