Re: compound propositions

From: David BL <>
Date: Wed, 17 Mar 2010 22:41:00 -0700 (PDT)
Message-ID: <>

On Mar 18, 12:28 am, paul c <> 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?

> 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 ...".

> 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?

> Some people talk about relation or relvar names having no meaning, then
> in the next breath assume that two names (such as R1 and R2 above) must
> have different predicates. I presume the reason is that if R1 and R2
> had different values they would contradict each other unless the
> predicates were different. That seems like meaning to me but it is a
> meaning that can't be respected in the results of an algebra that
> doesn't operate on relation names.

I fail to see the problem. ISTM you could just as well claim you can't multiply a speed by a time to get a distance because the multiplication operator only operates on a pair of numbers to give a number. Can you explain what you mean? Received on Thu Mar 18 2010 - 06:41:00 CET

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