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>
>
> 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.
>
> 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!
Date: Sat, 28 Nov 2009 17:56:36 -0400
Message-ID: <4b119c99$0$5326$9a566e8b_at_news.aliant.net>
paul c 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/y9e4vxhReceived on Sat Nov 28 2009 - 22:56:36 CET