Re: ?? Functional Dependency Question ??
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 21 Oct 2008 13:19:28 -0300
Message-ID: <48fe0123$0$5499$9a566e8b_at_news.aliant.net>
>> Consider that in the FD world symbol X represents a set of attributes
>> from some relation R. Let some tuple of R be given. Then as a
>> proposition we interpret X as implying that we are given or can deduce
>> (for the given tuple) the values of all the attributes associated with
>> X. This interpretation makes it obvious that unions of attributes
>> map to logical conjunctions, and that an FD maps to a logical
>> implication.
>
> Thanks, but how does that interpretation work when R has no attributes?
Date: Tue, 21 Oct 2008 13:19:28 -0300
Message-ID: <48fe0123$0$5499$9a566e8b_at_news.aliant.net>
paul c wrote:
> David BL wrote: > ... >
>> Consider that in the FD world symbol X represents a set of attributes
>> from some relation R. Let some tuple of R be given. Then as a
>> proposition we interpret X as implying that we are given or can deduce
>> (for the given tuple) the values of all the attributes associated with
>> X. This interpretation makes it obvious that unions of attributes
>> map to logical conjunctions, and that an FD maps to a logical
>> implication.
>
> Thanks, but how does that interpretation work when R has no attributes?
The same way DEE works with join. Received on Tue Oct 21 2008 - 18:19:28 CEST