Re: NULLs: theoretical problems?

"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:46cf6f34$0$4021$9a566e8b_at_news.aliant.net...
> Jan Hidders wrote:
>
>> On 24 aug, 16:35, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
>>
>>>Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote
>>>innews:famjo6$i68$1_at_orkan.itea.ntnu.no:
>>>
>>>
>>>>In other words, the DEF query is equivalent to
>>>
>>>>SELECT * FROM t WHERE t.a IS NOT NULL AND (t.a = 5 OR TRUE)
>>>
>>>My understanding was that the DEF as written was a shorthand:
>>>
>>>e.g.
>>>'def(x):((x or y) and x)' -> '((def(x) or y) and def(x))'
>>>
>>>You may be right, but then why the formula was not written with an
>>>explicit 'and' ?
>>
>>
>> Because it does not satisify all the logical laws of an AND, so to
>> avoid confusion another notation is used. Since it's related to an
>> existential quantifier a similar notation was chosen (think of EXISTS
>> x : f).
>>
>> And, yes, as Jon correctly remarked it is in fact equivalent with
>> something you can already write in SQL so you could achieve the same
>> with some self-discipline.
>
> Let me suggest the use of 6th normal form and then EXISTS is all one would
> need.

This is ludicrous. 6NF has nothing to do with null. If there cannot always be a value for a non-prime attribute in a relation, then the relation is not in 5NF, and as a consequence, exhibits an update anomaly in that the value must always be supplied. Received on Sat Aug 25 2007 - 02:22:03 CEST