Re: Advanced SQL

"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.

-- 
David Portas