Re: teaching relational basics to people, questions

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 28 Nov 2009 17:56:36 -0400
Message-ID: <4b119c99$0$5326$9a566e8b_at_news.aliant.net>



paul c wrote:

> Mr. Scott wrote:
>

>> But what if there is more than one row?  The information content of a 
>> table is the logical sum (disjunction) of the information represented 
>> by each row.

>
> The conventional view is that is that the information in a table is the
> logical conjunction of the information represented by the rows in the
> table. Just because the table is formed by a summing operation doesn't
> change that.

Ahem. Conjunction of the domains. A relation is the extension of a predicate. That predicate can be represented as the disjunction of the tuples.

>> But those can easily be transformed into into truth-valued 
>> constraints, can't they?

>
> Not easy if users aren't required to know default values. I don't see
> why they should. Contrary to Dr. Strangelove, the whole point of
> defaults is to avoid users having to know them!

Defaults are not constraints.

-- 
is there something in it for them, like maybe bailouts, if they can 
panic us into doing something politically to cover them?

November 19, 2007 - John S Bolton

http://tinyurl.com/y9e4vxh
Received on Sat Nov 28 2009 - 15:56:36 CST

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