Re: Love or hate, or? domains with cardinality two

Op donderdag 19 november 2015 19:46:33 UTC+1 schreef Erwin:
> Op woensdag 18 november 2015 10:10:04 UTC+1 schreef Nicola:
> > ...
> > >
> > > Okay so that was too hasty of me.
> > >
> > > (DEPARTMENT NOTMATCHING (EMPLOYEE WHERE mgr)) SUBSET-OF FI
> > >
> > > addresses it, methinks. Still nowhere near "not straightforward" in my
> > > book ...
> >
> > Point taken.
> >
> > This highlights the importance of the succintness of the language, not only the
> > expressiveness. Constraints expressed algebraically are in many cases
> > more succint
> > than their counterpart in first-order logic (think of division).
>
> I have been "hatching" quite a bit on a [polite] way to express that your "non-straigthforwardness" was actually not in the constraint, but in the language used by formal logic to express it.
>
> It is easy to deduce from "all departments must have exactly one manager" that "departments at fault are those that have no manager at all, or more than one". And while you _NEED_ logic to underpin that deduction, the language of logic itself is actually actively alienating/obstructive to making it. At least to an engineer whose profile perhaps doesn't fit the targeted audience of this group. This group being the theory group.
>
> In my personal opinion, which I am exceptionally going to label explicitly as "humble", that might very well be the reason why Datalog is not [and never will be] the solution to the "problem" of relational databases. (I know full well what amount of flak I'll get over such pronouncements in academic circles.)

I sincerely doubt you will need your flak jacket for that. :-) I personally would argue that datalog (and its variants, and extensions) is in some respects one of the most elegant ways of expressing a certain class of queries. But that does not mean I think it is "the solution" for expressing all relational queries ever. Never mind constraints, it was not designed for that.

I'm not even sure I would agree with the assumption you seem to be making that there is such a thing as "the solution". Why not different languages for different purposes and users? Just as long as it has a clear semantics and a mapping to a well understood logic.

  Jan Hidders Received on Wed Dec 02 2015 - 17:59:59 CET