Re: equivalence of functional dependencies
From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Fri, 09 Jan 2004 04:32:45 GMT
Message-ID: <N9qLb.1155$Pg.874_at_newsread1.news.pas.earthlink.net>
>>I have tried an example from the elmasri book, perhaps somebody can pass
>>judgement on my logic,
>>
>>two sets of functional dependencies F= {A > C, AC > D, E > AD, E > H}
>>and G = {A > CD, E > AH}. Check whether or not they are equivalent.
>>
>>here I make conclusion that they are not equivalent
Date: Fri, 09 Jan 2004 04:32:45 GMT
Message-ID: <N9qLb.1155$Pg.874_at_newsread1.news.pas.earthlink.net>
Adrian Kubala 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.
How do you derive C -> D from F? It can't be from AC -> D, but I don't see where else you can think it comes from either.
-- Jonathan Leffler #include <disclaimer.h> Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com Guardian of DBD::Informix v2003.04 -- http://dbi.perl.org/Received on Fri Jan 09 2004 - 05:32:45 CET