Re: Does entity integrity imply entity identity?
Date: Sun, 02 Aug 2009 11:32:33 -0300
David Portas wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>>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 "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