Re: Does entity integrity imply entity identity?
Date: Sun, 02 Aug 2009 02:30:28 -0300
Message-ID: <4a75247b$0$23740$9a566e8b_at_news.aliant.net>
Mr. Scott wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4a7479f3$0$23783$9a566e8b_at_news.aliant.net...
>
>>Mr. Scott wrote:
>>
>>>Since the entity integrity rule ensures that a relational table cannot
>>>have any duplicate rows, does that imply that each row in a table maps to
>>>a distinct entity?
>>
>>I am unfamiliar with an entity integrity rule. It sounds like some shit
>>somone just made up to market ER diagrams.
>
> I thought Codd referred to the the entity integrity and referential
> integrity rules as the insert-update-delete rules of the relational model.
Can you cite a reference for that?
> The entity integrity rule requires that no primary key value or part of a
> primary key value can be missing, which ensures that there can be no
> duplicate rows in a relational table.
That sounds more like the guaranteed access rule, which is sometimes referred to as logical identity.
>>http://en.wikipedia.org/wiki/Codd's_12_rules >> >>The guaranteed access rule is sometimes called the logical identity rule.
>
> Does that mean that entity integrity implies entity identity? Is logical
> identity the same thing as entity identity?
I am unaware of anything called an entity in either the algebra or the calculus. The guaranteed access rule is sometimes referred to as logical identity.
http://en.wikipedia.org/wiki/Identity_of_indiscernibles Received on Sun Aug 02 2009 - 07:30:28 CEST