Re: equivalence of functional dependencies

From: Bert Blink <bblink_at_pcug.org.au>
Date: Sun, 11 Jan 2004 08:44:08 +1100
Message-ID: <k3s000dr6nbd8mbc1efb9kjm8hk4jt0bte@4ax.com>

Not sure what the problem here is but F & G are certainly equivalent, ie when reduced to a "minimal set of FDs" they both reduce to the following set of FDs

A --> B
A --> C
A --> D

C, D --> E

A --> E (the extra FD in G) is derivable from the above by

A --> C
A --> D

hence

A --> C, D --> E

and hence transitively A --> E

On Thu, 8 Jan 2004 19:46:17 -0600, Adrian Kubala <adrian_at_sixfingeredman.net> wrote:

>shannon <shannon_at_nolunchmeat.com> schrieb:
>> I have tried an example from the elmasri book, perhaps somebody can pass
>> judgement on my logic,
>>
>> two sets of functional dependencies F= {A > C, AC > D, E > AD, E > H}
>> and G = {A > CD, E > AH}. Check whether or not they are equivalent.
>>
>> here I make conclusion that they are not equivalent,
>
>I don't know about the official way to do this, but by inspection C > D
>is derivable from F but not G, so they can't be equivalent.
Received on Sat Jan 10 2004 - 15:44:08 CST