Re: compound propositions

From: Joe Thurbon <>
Date: Tue, 16 Mar 2010 18:08:33 +1000
Message-ID: <op.u9nh8kllq7k8pw_at_imac-3.local>

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.


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. Received on Tue Mar 16 2010 - 09:08:33 CET

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