Re: Advanced SQL

From: David Cressey <cressey73_at_verizon.net>
Date: Fri, 07 Sep 2007 21:40:21 GMT
Message-ID: <9zjEi.11$yf3.3@trndny06>

"David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message news:zumdnU5LucVJMHzb4p2dnAA_at_giganews.com...
> "Evan Keel" <evankeel_at_sbcglobal.net> wrote in message
> news:Np%Di.5257$JD.656_at_newssvr21.news.prodigy.net...
> >
> > "David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message
> > news:pZSdnfih_oRy5H3bRVnyigA_at_giganews.com...
> >> "David Cressey" <cressey73_at_verizon.net> wrote in message
> >> news:HBTDi.14699$tB2.1005_at_trndny05...
> >> >
> >> > There are two webistes I can recommend:
> >> >
> >> >
> >

http://www.utexas.edu/its-archive/windows/database/datamodeling/dm/overview.html
> >> >
> >> > For an overview to data modeling and database design.
> >> >
> >> > and
> >> >
> >> > http://www.databaseanswers.org/
> >> >
> >> > For about 200 free database designs, covering many common problems.
> > You
> >> > will want to revise the design to suit your own requirements.
> >> >
> >> >
> >> >
> >>
> >> Call me picky but I am not entirely comfortable with that U.Texas site,
> > even
> >> though it's a commendable effort overall.
> >>
> >> "The relational model represents data in the form of two-dimension
> >> tables"
> >> "A relational table is a flat file ..."
> >> "Primary and foreign keys are the most basic components on which
> > relational
> >> theory is based."
> >> "The definition of second normal form states that only tables with
> > composite
> >> primary keys can be in 1NF but not in 2NF"
> >
> > They have it right here. All non-key attributes must be dependent on the
> > full key. Only applies to tables with keys composed of multiple columns>
> >
> >> "The third normal form requires that all columns in a relational table
> >> are
> >> dependent only upon the primary key"
> >
> > They have it right again. No transitive dependecies. So the problem? Oh
> > yes,
> > remove the candidate key in this test.
> >>
> >>

http://www.utexas.edu/its/windows/database/datamodeling/rm/overview.html
> >> http://www.utexas.edu/its/windows/database/datamodeling/rm/rm1.html
> >> http://www.utexas.edu/its/windows/database/datamodeling/dm/keys.html
> >> http://www.utexas.edu/its/windows/database/datamodeling/rm/rm7.html
> >>
> >> --
> >> David Portas
> >>
> >>
> >
> >

>

> The case already mentioned by Jon is one exception to the statement about
> 2NF.

>
> Normalization is concerned with candidate keys not just primary keys, so
the
> definitions are necessary conditions but not sufficient ones.
>
Yes. You will note, IIRC, that the website discusses normalization repeatedly as if the primary key were the only key under consideration. Indeed, when I first learned normalization, I learned it this wrong way. Not from this website, but from another source.

> --
> David Portas

>
> Received on Fri Sep 07 2007 - 16:40:21 CDT