Re: Does entity integrity imply entity identity?
Date: Wed, 5 Aug 2009 19:30:27 -0400
Message-ID: <iMudnZFco-WOi-fXnZ2dnUVZ_jSdnZ2d_at_giganews.com>
"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? Is there a reasonable alternative? What I mean is, is there an alternative that can be implemented using existing commercial DBMS? Darwen advocates splitting a table that allows nulls into a bunch of relations that don't, but there are problems with that approach. One is the need for a bunch of interrelational constraints, some of which are extremely difficult if not impossible to implement using existing DBMS. Another is the need for multiple assignment to avoid violating some of those interrelational constraints. Darwen's approach seems to me like it's more trouble than it's worth. Do you know of another approach? Received on Thu Aug 06 2009 - 01:30:27 CEST