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Re: Advanced SQL

From: Evan Keel <evankeel_at_sbcglobal.net>
Date: Thu, 06 Sep 2007 22:45:01 GMT
Message-ID: <Np%Di.5257$JD.656@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
>
>
Received on Thu Sep 06 2007 - 17:45:01 CDT

Original text of this message

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