Re: Does entity integrity imply entity identity?

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.

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.

> What I mean is,
> is there an alternative that can be implemented using existing commercial
> DBMS?
Of course. Simply don't use NULL.

<snip>

> Do you know of another approach?

Yes. Thinking is a fine approach. Received on Thu Aug 06 2009 - 02:21:38 CEST