Re: compound propositions

From: paul c <>
Date: Tue, 16 Mar 2010 17:18:06 GMT
Message-ID: <i3Pnn.71176$PH1.48378_at_edtnps82>

Joe Thurbon wrote:
> On Tue, 16 Mar 2010 05:12:55 +1000, paul c <> wrote:
> [...]

>> One reason is that I still don't know how Codd's Information Principle 
>> applies to compound propositions, eg., " 'C1' is a customer OR 'C1' is 
>> a client".  I can see that humans might imagine themselves capable of 
>> interpreting a relation (or to put it redundantly a relation value) as 
>> implitly mentioning that 'OR' connective (and dba's might so instruct 
>> their users).  But where is it recorded?  (or 'manifested'?)  Eg., is 
>> it 'recorded' only in the ephemeral form of an expectation that a 
>> program's execution can't manifest given a single relation to operate on?

> Hi Paul,
> As far as I can tell:
> 'The algebra' is a method of querying a database for things that it does
> or does not entail.
> 'The database' is a set of assertions (I'm considering only base
> relations).
> I think that your question is 'can we assert disjunctions in the
> database, so that they can be operated on logically by the algebra?'
> The answer is, I think, no. At least not while the CWA is present.
> Cheers,
> Joe
> P.S. My understanding is that the equivalence between the algrbra and
> FOL is about the proof-theory side of things, and that FOL has a
> strictly richer expressiveness in terms of what the database (cf.
> theory) can express.

Joe, I'm not surprised that my typically clumsy question is diverging, if it converges into a better one I'll consider that as much progress as an answer. The only comment I have right now is that I don't think databases have base relations! Whether a relation is base seems to depend on a particular usage, such as within an algebraic expression. So

   a relation might be 'base' in one program and not in another even though both involve the same database. Received on Tue Mar 16 2010 - 18:18:06 CET

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