Re: Codd's Information Principle

On 4 nov, 18:23, paul c <toledobythe..._at_oohay.ac> wrote:
> Bob Badour wrote:
> > paul c wrote:
> ...
> >> Do you mean certain negations and disjunctions aren't amenable, such
> >> as the predicate "it is not the case that the temperature T in city C
> >> is T degrees"?
>
> >> (Thanks for the precision, still pondering the rest.)
>
> > No. First, you have T representing 2 different measures so I cannot
> > understand your example.
>
> > I mean the predicate for "Employee, EmpID, manages department, DeptNo"
> > is too complex to calculate or to represent algebraically. It has all
> > sorts of complex factors that generally never get recorded anywhere such
> > as someone had to apply for a job with the company and that person had
> > to perform well enough to get promoted to management (not necessarily at
> > this company) etc.
> > ...
>
> And thank goodness for that!
And you have not heard the best part...yet...

I would be glad to hear how we establish a valid quantifier in relational algebra using only internal predicates. The lack of clarification of the external predicate, while being symptomatic limitation of traditional RM relational theorists gladly recognize, does not bother them much when it comes to operate relations algebrically using only the internal predicate. That's where domain analysis becomes handy...

Regards... Received on Thu Nov 05 2009 - 19:54:06 CET