Re: How core is Core?

On Jul 4, 2007, at 9:32 AM, Dave Reynolds wrote:

> Bijan Parsia wrote:
>
>> The strongest thing I'd personally say is that there will be  
>> multiple implementations of DL Safe SWRL rules in owl engines  
>> which will want to exchange rulesets with each other and with  
>> other systems as appropriate. I believe that the user base will be  
>> pretty happy with that.
>
> Seems reasonable. Would that community be happy with continuing to  
> use DL Safe SWRL for interchange or is there some additional need  
> that a compatible RIF dialect would satisfy?

Syntactically, currently there is no way to indicate that a rule is  
intended to be DL Safe. Also, the old SWRL syntax has some bugs and  
will probably need updating to reflect OWL 1.1 (and SPARQL)  
developments. I believe, from the general discussion at OWLED, that  
pretty much everyone would be happy with some useful convergence with  
the RIF. So if it were easy to define a usable dialect of RIF that  
captured DL safe SWRL rules as extensions to OWL ontologies, that  
would be a no brainer for the canonical syntax (IMHO). Otherwise, I  
think there would still be a strong enough desire to be able to  
interoperate via RIF that people would define mappings to an  
appropriate dialect. Speaking as a user and an implementor (both of  
reasoners and editors) this is certainly what I'll be looking for.

>> (This, of course, says nothing specific about what "goes into" Core.)
>
> Quite so.
>
>>> 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

> 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), 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 08:53:03 UTC