MESSAGE
| DATE | 2014-12-18 |
| FROM | Ruben Safir
|
| SUBJECT | Re: [LIU Comp Sci] Normalization review
|
From owner-learn-outgoing-at-mrbrklyn.com Thu Dec 18 13:02:22 2014
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Date: Thu, 18 Dec 2014 13:02:21 -0500
From: Ruben Safir
To: learn-at-mrbrklyn.com
Subject: Re: [LIU Comp Sci] Normalization review
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those slides 6-56 and 6-55 , I've been staring at the text book all
night to make sense of that section.
That does not explain how you get to where you need to be, and it
doesn't explain what the function PROJECT(x) ACTUALLY is. That should
be the set of ALL tuples in Project.
On Thu, Dec 18, 2014 at 12:57:19PM -0500, Ruben Safir wrote:
> Ah - but that is the same as the text book.
>
> It says, for example:
>
> The only free tuple variables in a relational calculus expression should
> be those that appear to the left of the bar ( | ).
> In above query, t is the only free variable; it is then bound
> successively to each tuple.
>
> WHY? What is the point of the bar and what does it matter if a tupple
> variable is free or bound?
>
> This should have been tought FIRST, in the first two weeks and driven
> into us over the entire semester. This is tough and important stuff.
>
> Ruben
>
|
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