Re: Does entity integrity imply entity identity?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 06 Aug 2009 13:26:31 -0300
Message-ID: <4a7b0438$0$23781$9a566e8b_at_news.aliant.net>
>>Mr. Scott wrote:
>>
>>
>>>"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?
>>
>>By stating so in the database. That's what relations do: make statements.
Date: Thu, 06 Aug 2009 13:26:31 -0300
Message-ID: <4a7b0438$0$23781$9a566e8b_at_news.aliant.net>
Mr. Scott wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message > news:4a7a425c$0$23748$9a566e8b_at_news.aliant.net... >
>>Mr. Scott wrote:
>>
>>
>>>"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?
>>
>>By stating so in the database. That's what relations do: make statements.
> > How, exactly? If you have columns K, A, B, and C such that for a given K it > is permissible for the values for A, B or C to be at present unknown, but > not both A and B, how would you lay out the tables and referential > constraints without using nulls?
{K,A,B}
{K,C}
Received on Thu Aug 06 2009 - 18:26:31 CEST