Re: compound propositions
Date: Tue, 16 Mar 2010 17:18:06 GMT
Joe Thurbon wrote:
> On Tue, 16 Mar 2010 05:12:55 +1000, paul c <toledobythesea_at_oohay.ac> 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
> 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.
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.
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