Re: Does entity integrity imply entity identity?

From: Bob Badour <>
Date: Sun, 02 Aug 2009 02:30:28 -0300
Message-ID: <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 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.

>>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. Received on Sun Aug 02 2009 - 07:30:28 CEST

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