Re: Does entity integrity imply entity identity?

From: Bob Badour <>
Date: Sun, 02 Aug 2009 11:32:33 -0300
Message-ID: <4a75a387$0$23742$>

David Portas wrote:

> "Bob Badour" <> wrote in message
> news:4a75247b$0$23740$

>>Mr. Scott wrote:
>>>"Bob Badour" <> wrote in message 
>>>>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 
>>Can you cite a reference for that?

> The "RM/T" paper, Extending the Database Relational Model to Capture More
> Meaning, ACM TODS, Vol. 4, No. 4, December 1979:
> "Rule 1 (entity integrity): No primary key value of a base relation is
> allowed to be null or to have a null component."
> It therefore originates from the point at which Codd decided to "extend" the
> model with E-relations, nulls and other exotic things. The rule begs more
> questions than it answers (what about derived relations and relations with
> multiple keys?). Myself and likeminded people are happy with the concept of
> a pre-RM/T relation that needs no such rules.

Ah, yes. Codd introduced a lot of things in RM/T and RM/V2 that other relational proponents find questionable. Received on Sun Aug 02 2009 - 16:32:33 CEST

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