Re: Does entity integrity imply entity identity?

"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message news:4a7a22e9$0$23782$9a566e8b_at_news.aliant.net...
> Bob Badour wrote:
>
>> Mr. Scott wrote:
>>
>>> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>>> news:4a799414$0$23781$9a566e8b_at_news.aliant.net...
>>>
>>>> Mr. Scott wrote:
>>>>
>>>>> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>>>>> news:4a784836$0$23766$9a566e8b_at_news.aliant.net...
>>>>>
>>>>>> Mr. Scott wrote:
>>>>>>
>>>>>>>> The entity integrity rule is generally presented as a subrule under
>>>>>>>> Codd's rule 10.
>>>>>>
>>>>>> I don't know why you would say that when the description of the
>>>>>> so-called "entity integrity" basically restates Rule 2 verbatim.
>>>>>
>>>>> I don't think that's true. Although the entity integrity rule implies
>>>>> the guaranteed access rule, the guaranteed access rule doesn't imply
>>>>> the entity integrity rule. The guaranteed access rule doesn't say
>>>>> anything at all about nulls.
>>>>
>>>> As Martha would say: This is a good thing. Null was a bad idea in the
>>>> first place.
>>>
>>> Why was it a bad idea?
>>
>> Entire books have been written on that subject. I suggest you read one or
>> two of them. See for example Date's various _Writings..._ books.
>>
>>
>>> Is there a reasonable alternative?
>>
>> Yes. Nothing at all is a reasonable alternative to anything as bad as
>> null. If it ain't broken, don't try to fix it. If it is broken, don't
>> break it worse.
>
> Perhaps I should clarify: Your question amounts to asking if one has a
> reasonable alternative to poking oneself in the eye with an icepick.

If the requirement is to record in the database as much information as is available, then how can the fact that a value is at present unknown be recorded? The fact that there is supposed to be a value is available information. The fact that the value is at present unknown is also available information. If those facts are not recorded, then the requirement is not being met. Null is one way to record that a value is at present unknown. I don't see how asking if there is a reasonable alternative to null amounts to asking if one has a reasonable alternative to poking oneself in the eye with an icepick. Received on Thu Aug 06 2009 - 04:32:51 CEST