Re: Examples of SQL anomalies?

"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:486f7bfa$0$4047$9a566e8b_at_news.aliant.net...
> goanna wrote:
>
>> Marshall <marshall.spight_at_gmail.com> writes:
>>
>>>What can be meaningfully asked is determined by the schema.
>>
>> Close. What can be meaningfully asked is determined by the meaning
>> of the schema. In the case of nullable attributes, this must be
>> specified, not guessed.
>>
>>
>>>If the schema specifies that the weight attribute is nullable,
>>>then the question of how much a shipment weighs in total
>>>is a question that cannot be asked.
>>
>> If the schema specifies that the weight attribute is nullable,
>> we need to know what, precisely, is the intended meaning of a
>> null weight. If may mean that the weight is unknown, or it may
>> mean that the weight attribute is not applicable to this entity
>> (e.g. the weight of an electronic book), or it may mean ...
>> In a badly designed schema it may unfortunately be used with
>> more than one meaning without permitting them to be distinguished.
>>
>> Nulls are often but not exclusively used to mean unknown value.
>> Failure to distinguish between different uses of null is the
>> basis of most of these, rather pointless, arguments.
>
> I disagree. Ignorance is the basis of these rather pointless arguments.
> The whole idea of NULL or missing markers has been thoroughly refuted as a
> useful idea.

Only if you reject reality and substitute your own. Received on Sat Jul 05 2008 - 16:12:25 CEST