Re: compound propositions
Date: Thu, 18 Mar 2010 16:37:37 GMT
David BL wrote:
> On Mar 18, 12:28 am, paul c <toledobythe..._at_oohay.ac> wrote:
>> My attitude is that 'partial information' is too nebulous a term to be >> useful because it amounts to the same thing as 'missing information'.
> Yes it's the same thing, but why is it too nebulous?
It's nebulous because so many people preface their requirements with it when a grade-schooler is capable of asking how a dbms can operate on something that is missing. Even if everybody agrees it's missing, 'not there', nobody can put their finger on it. The "Emperor's New Clothes" were also nebulous in this way.
>> If we can't be bothered to record (eg., provide a suitable attribute) or >> otherwise stipulate that a supplier is on the northside or wherever, we >> shouldn't expect a dbms to respect the stipulation, because that >> information is not available to its operators.
> Sorry don't know what you mean by 'respect the stipulation'. I read
> that as a simple tautology: "if specifying x is optional then don't
> expect dbms to require x because ...".
Without some kind of location attribute how do you stipulate to a dbms that a supplier is located on the 'northside'? The context of a db might require that all suppliers are on the northside but that doesn't affect the behaviour of the dbms, only its usage. (Obviously Codd meant his Information Principle to prevent other arbitrary behaviours as well, eg., ones based on 'physical' position.)
>> Eg., the typical algebra doesn't operate on relation names, only >> relation values.
>> As far as a relational dbms is concerned the inclusion >> of 'northside' or 'southside' in some unrecorded predicate is >> irrelevant. A better label for partial information would be >> 'non-existent information', which might help to underline its irrelevance.
> Irrelevance to what?
The purpose of using a dbms to manipulate or record information. Received on Thu Mar 18 2010 - 17:37:37 CET