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

Op woensdag 2 december 2015 18:00:03 UTC+1 schreef Jan Hidders:
> 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

There appear to be academic circles who regard "relational databases" as a "solved problem" with "the solution" being Datalog.

Efforts such as Rel tend to piss off [the people in] those circles quite seriously, I'm told, because "it distracts attention from where the real problem is and therefore holds back true progress".

Not my words and some exaggeration might have slipped in during paraphrasal, but the gist of the message was preserved.

Your remark re. "not designed for constraints" puzzles me because all in all, a constraint [declaration] is nothing more than a predicate. Hard to imagine it being claimed that "Datalog is not designed for handling predicates" !!! (Have you seen Martinenghi's work ?) Received on Mon Jul 25 2016 - 21:21:00 CEST