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

On Jul 12, 8:21 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> "Cimode" <cim..._at_hotmail.com> wrote in message
>
> news:1184260798.451810.60010_at_g4g2000hsf.googlegroups.com...
>
>
>
> > On 12 juil, 18:25, "David Cressey" <cresse..._at_verizon.net> wrote:
> > > "Cimode" <cim..._at_hotmail.com> wrote in message
>
> > >news:1184247582.799847.27210_at_o61g2000hsh.googlegroups.com...
>
> > > > On Jul 12, 2:15 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> > > > > "Jan Hidders" <hidd..._at_gmail.com> wrote in message
>
> > > > >news:1184241371.515071.251680_at_k79g2000hse.googlegroups.com...
>
> > > > > > On 11 jul, 22:25, Cimode <cim..._at_hotmail.com> wrote:
> > > > > > > Furthermore...
> > > > > > > <<Technically a PK is *only* a physical implementation device,
> not a
> > > > > > > logical concept at all.>>
>
> > > > > > `When I use a word,' Humpty Dumpty said, in rather a scornful
> tone,
> > > > > > `it means just what I choose it to mean -- neither more nor less.'
>
> > > > > > `The question is,' said Alice, `whether you can make words mean so
> > > > > > many different things.'
>
> > > > > > `The question is,' said Humpty Dumpty, `which is to be master --
> > > > > > that's all.'
>
> > > > > > ;-)
>
> > > > > > To answer the question, I think that is quite simple. As defined
> in
> > > > > > the relational model it is a logical concept. As far as I know the
> SQL
> > > > > > standard does not state that a PK implies an index (but I could be
> > > > > > wrong) and then it is also there a logical concept. If it does
> imply
> > > > > > an index then it is mixed concept because it has both logical and
> > > > > > physical consequences.
>
> > > > > > -- Jan hidders
>
> > > > > It was my understanding that the relational model defines keys, but
> not
> > > > > primary keys. That is, any candidate key is as much of a key as any
> > > other.
> > > > In a relational perspective, the term *primary key* was first used by
> > > > Codd to designate a specific unique identifier that allows to
> > > > distinguish tuples.
>
> > > > > It was my understanding that certain schools of data management,
> > > including
> > > > > the SQL school, adopted the convention of naming one candidate key
> as
> > > > > primary key, and of making all FK references refer to that key,
> where
> > > > > possible. I can see, and use, that practice myself. But I can't
> see
> > > where
> > > > > the relational model necessitates it.
> > > > Who cares what SQL schools of *management* have to say about
> > > > relational model?
>
> > > Please don't confuse "management" with "data managment".
> > I think I misread your comment (did not mean to sound offending).
>
> Yes, I think you did.
Sorry about that but a fact is a fact. *SQL school* does not have anything productive to say about theory of relations.

> > I
> > thought you were advocating that SQL schools of data management have
> > any relevance anymore as to what should and should not be relationally
> > sound. Quite frankly, I do not pay any attention to anything that is
> > SQL related (except to make a living)..
>
> SQL oriented people (I might include myself) will advocate declaring a
> primary key whenever a table is created, and making all FK references to
> the table via its primary key. That turns out to be of value even if the
> 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. Received on Fri Jul 13 2007 - 10:25:10 CEST