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

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:Hweoe.110129$zI7.6623283_at_phobos.telenet-ops.be...
> mountain man wrote:
>>
>> There have been, there are,
>> and there always will be
>> NULLS in the real world.
>
> NULLs are an abstraction and like all abstractions they do not really
> exist.

Information is an abstraction which may or may not exist. If it exists I call it data or information. But if it does not exist (within the DBMS) for any given reason, then it is called "missing", void, or null.

> The relevant question here is if they are necessary and useful to describe
> the world.

Very useful.

>> Does this fact not conflict
>> with Date's wants, and if
>> so, why does Date want
>> to ignore them?
>
> They unnecessarily complicate the model.

The model cannot be complicated by essences of reality. In reality, information may be partial, and thus have elements in it which have null values.

> Anything that can be modeled with them can also be modeled without them,
> and to the extent that they are convenient this is mostly due to the fact
> that the possibilities for user-defined domains were too restricted.

Modelling holes in information is straightforward with the use of nulls. You either have them, or you dont. You could probably replace then with a value, say x, but what would this gain?

-- 
Pete Brown
IT Managers & Engineers
Falls Creek
Australia
www.mountainman.com.au/software