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Re: Database Theory - Keys and functional dependencies?

From: Daniel Guntermann <guntermann_at_uswest.net>
Date: Wed, 13 Feb 2002 07:18:46 -0800
Message-ID: <Ljva8.12$yO1.22730@news.uswest.net>

"Christian Hoecht" <choecht_at_web.de> wrote in message news:a4b0c1$tmo$1_at_news.online.de...
:
> Find out all Keys (Primary/Foreign) for the following Relation-Types
> and the kind of Normalization (1NF, 2NF, 3NF, BCNF):
>
> a) R1 (A,B,C,D)
> A -> B
> B -> A
> AC -> D

I've left the steps of finding the closure sets of attributes and deriving the irreducible sets of dependencies out...

PK - AC
Alternative candidate key - BC
3NF (Not in BCNF because the two candidate keys overlap and have C attribute in common).

> b) R2 (A,B,C,D,E)
> ABC -> D
> B -> E
> A -> C
>

Primary key - AB
1NF - Nonkey attributes are not irreducibly dependent on the primary key.

> c) R3 (A,B,C,D,E,F)
> A -> B
> D -> B
> CE -> AD
> A -> F

Primary key - CE
2NF - Meets criteria for 1NF and 2NF, but contains transitive dependencies.

>
> Thank you for your support!

Your welcome!
>
> Christian Hoecht
>

HTH, Dan Guntermann Received on Wed Feb 13 2002 - 09:18:46 CST

Original text of this message

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