Re: set-valued values

paul c wrote:
> Another maybe crazy question - if instead of 'atomic values' (whatever
> that means) a relational engine (note for David, I've avoided using the
> term 'DBMS' !) expressed only values made up of sets, would the presence
> of the empty set in both true and false extensions create any problems?
> (I'm thinking that the relational requirement of attribute names means
> there is no problem, eg., the presence of empty sets is just an artifact
> of the mechanism that can usually be safely ignored.)
>
> As for representation, sometimes such values can't be represented
> without access to other 'attributes', eg., values that are internal to
> an engine. My attitude (no reasoning involved I'm afraid to say) is
> that it's okay to give the builtin result 'true' in such cases. That
> way, the engine can proceed to manipulate the expression if further
> requests of made of it, concerning that result.
>
>
> p

One reason I asked this question is because Codd started with sets, then veered away from them in a way, I'm guessing because of such possible problems, whereas the singleton value has a logical complement that is easily recognized if one knows its domain. It's always puzzled me why he avoided sets when it came to the down and dirty of implementations.

p Received on Fri Dec 08 2006 - 01:27:15 CET