RE: How core is Core?

> From: public-rif-wg-request@w3.org
[mailto:public-rif-wg-request@w3.org]
> On Behalf Of Bijan Parsia
> 
> On Jul 4, 2007, at 9:32 AM, Dave Reynolds wrote:
> 
> > Bijan Parsia wrote:
> >
...
> >>> This subset of Core is implementable in both production rule and
> >>> LP settings.
> >> [snip]
> >> I thought a sticking point was recursion?
> >
> > I don't think so, I believe the issue is the ability to build
> > recursive data structures.
> 
> Well, I recall that the last time this discussion occurred, the point
> was that PR systems generally didn't have recursive rules and that it
> was not desirable to add them, e.g.:
>
http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0103.html

[PV>] I'm pretty sure that 100% of implemented PR-engine rules (ie
millions) do not do "recursion" as meant* here, implying this core
feature would simply not be used in RIF PR. A RIF PR translator could
optionally handle a recursive rule as a recursive method.

* PR rulesets that do lots of inferencing to solve complex planning etc
problems probably do a "form" of recursion, but in the style that
several rules cooperate and repetitively cause new inferences to
existing rules in order to solve a problem. Of course, they do this by
updating data (aka asserting new facts) which cause rules, which may
have already fired for other data, to fire again.
> 
> > Certainly is known (e.g. [1]) that for both datalog and semi-
> > positive datalog[*] the production style fixed-point semantics and
> > the declarative (minimal model) semantics coincide.
> 
> Sure, but that's not at all the same as saying that practical systems
> based on one or the other approach happily coincide.
> 
> In any case, it seems to me that if you are going to force new
> features on a class of systems (which I do think is one
> legitimate...if tricky...thing for a standard to do), 

[PV>] I disagree on that point, but understand why some "standards"
efforts exist to "push the envelope" in developing technology. One could
argue for example that the entire semantic web effort is an attempt to
introduce a technology via a standard, rather than standardizing
existing (ie implemented) solutions. On the other hand, few PR vendors
would be upset to see a RIF PR++ that actually benefited users,
providing that RIF PR existed for all the existing users. On the other
hand, any requirements for RIF PR++ should come from said end-users (and
use cases), not from us. 

> it certainly
> needs to offer some clear benefit to the users of those system, if
> perhaps future ones. My impression is that PR/BR users don't miss
> recursive rules and implementing them sensibly would be very
> difficult. So either you clutter your code base with a naive
> implementation that pisses off the new people you were hoping to
> attract and consumes effort you could have spent improving your
> product for existing users, or you don't conform.
> 
> This is predicated on what Gary said in the above message still being
> au courant. I didn't see any subsequent discussion where Gary
> withdrew this point, but I didn't go that far :)
> 
> Cheers,
> Bijan.

Received on Wednesday, 4 July 2007 18:10:43 UTC