Re: dbdebunk 'Quote of Week' comment
Date: Sat, 27 Aug 2005 06:20:44 GMT
Message-ID: <0DTPe.2630$_84.2351_at_newsread1.news.atl.earthlink.net>
"Marshall Spight" <marshall.spight_at_gmail.com> wrote in message
news:1125095077.430231.119860_at_g49g2000cwa.googlegroups.com...
> David Cressey wrote:
> > "Marshall Spight" <marshall.spight_at_gmail.com> wrote in message
> > news:1125074070.799079.80320_at_z14g2000cwz.googlegroups.com...
> > > x wrote:
> > > >
> > > > This means that there must be a one to one mapping between the
generated
> > key
> > > > and some key with a meaning for the end user. Therefore that
meaningless
> > > > primary key is a pointer. But one of the goals of the relational
model
> > is to
> > > > eliminate pointers from the data model.
> > >
> > > I'm not sure I share this point of view. I propose that
> > > every pointer is meaningless; every key is meaningful,
> > > whether system generated or not. The meaning is exactly
> > > that it is the identity of the row. A randomly-generated
> > > customer id still means something.
> > >
> > I'm not sure I share YOUR point of view, either. I would suggest that
the
> > key is not the identity of the row, but the identity
> > of the entity described in the row. If we were to delete the row, and
then
> > insert another row with a different key, who is to say that the system
> > didn't reuse the unused row?
>
> I use the term "row" as a logical term, not a physical one.
I'm not following you. I *think* I use the term "row" as a logical one as well.
> >> > And the important thing, as far as I'm concerned, is that rows are
> > > Another difference between keys and pointers is that
> > > keys are content-addressible, while pointers are
> > > location-addressible.
> >
> > "unpinned" in the RM.
>
> Yes.
> >
> > In practice, this is only partly true. If the DBMS alters either the
> > content or the location of a row, it may have to do some index
maintenance
> > to reflect that change. But at least a row is unpinned except for the
pins
> > in the index.
>
> I think I'd just change this a tiny bit to say "In the implementation,
> this is only partly true."
Agreed, with one more tiny change: "In current implementations, this is only partly true"
> >
> Marshall
> Received on Sat Aug 27 2005 - 08:20:44 CEST