Re: ?? Functional Dependency Question ??

From: Bob Badour <>
Date: Tue, 21 Oct 2008 13:55:30 -0300
Message-ID: <48fe0995$0$5470$>

paul c wrote:

> Bob Badour wrote:

>> 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.

> I'm not sure about that. Maybe I'm being too literal in asking about
> this, but David B is talking about a mapping that involves values of
> attributes. I don't know what the value of "no attribute" is.

Regardless, it is a value. It can either exist in the relation or not. We can test it for equality. What else does one need to know about it? Received on Tue Oct 21 2008 - 18:55:30 CEST

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