Re: compound propositions

On Mar 15, 9:12 pm, paul c <toledobythe..._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?

I suspect you're assuming an entity point of view.

If Customer and Client are relations which represent the predicates in your example, and the two are exclusive, then in theory one could define referential constraints to exclude from each relation those values which exist in the other. If you have a Person relation which may only contain values which exist in either Customer or Client, then that too could be defined as a referential constraint. Received on Tue Mar 16 2010 - 16:11:20 CET