Re: Does entity integrity imply entity identity?

From: David Portas <>
Date: Sun, 2 Aug 2009 09:16:22 +0100
Message-ID: <>

"Bob Badour" <> wrote in message news:4a75247b$0$23740$
> Mr. Scott wrote:
>> "Bob Badour" <> wrote in message
>> news:4a7479f3$0$23783$
>>>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 "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.

David Portas
Received on Sun Aug 02 2009 - 10:16:22 CEST

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