Re: A pk is *both* a physical and a logical object.

From: David Cressey <>
Date: Fri, 13 Jul 2007 12:00:39 GMT
Message-ID: <HPJli.7363$CJ4.3078_at_trndny08>

"Cimode" <> wrote in message

> > SQL oriented people (I might include myself) will advocate declaring a
> > primary key whenever a table is created, and making all FK references
> > the table via its primary key. That turns out to be of value even if
> > primary key concept is outside of the relational model of data.
> I do not think the concept of primary key is anywhere *outside* the
> relational domain of investigation of database management as its
> concept of unique identifier was defined in relational theory well
> before SQL systems were born.
> I don't see the relevance nor intellectual honnesty into appropriation
> by SQL oriented people of the concept of unique identifier. For
> instance, tha fact that I use SQL on a daily basis because I need to
> make a living, does not prevent me from seeing how SQL breaks
> relational rules at every level and how SQL people (ANSI committee)
> perverted relational model probably because the were pressured by
> dbms editors. Considering the recent trends in dbms products, I would
> not be surprised for instance that XML would become a new SQL standard
> proponent. That would be a total antithesis to relational theory and
> a major regression in database management in general.

By bringing the "SQL school of data management" into the discussion, I did not intend to "appropriate" the concept of unique identifier (key, or candidate key) nor even the concept of "primary key". I specifically did NOT intend the inference that in order to advocate the selection and use of a primary key, one had to be of the SQL school of data management.

The only reason I brought SQL oriented people into the discussion was to describe a specific reason for naming one of the keys to be primary, a reason that may or may not be grounded in relational theory. It's my perception that the concept of primary key is not in fact grounded in relational theory, and that relational theory gets along just as well without it. I wanted either confirmation or refutation of that perception from this group.

It seems to me that, given that as a starting point, assuming you agree, you could either endorse or disparage the use of primary key without the necessity of endorsing or disparaging the entire community of SQL practitioners.

Specifically, does Tutorial D have the concept of "primary key" in it? If so, how does it relate to relational theory? If not, how does it address the same problems that lead SQL practitioners to lean on the concept of primary key? Received on Fri Jul 13 2007 - 14:00:39 CEST

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