Re: Classes and predicates as first class objects

Ian,

 I am sorry, I didn't mean to make this into an RDF vs DL issue. The 
only reason I focused on DLs is that the proposed model theories for OWL 
mirror that of DLs rather closely. I apologize if I created the 
impression that I was trying to pick on DLs.

 While it is true that text book renderings of FOL do not allow 
predicates as arguments to other predicates, they also don't make any 
mention of classes. For RDF, a class is not anything special. So, we 
should probably separate our treatment of classes from that of 
predicates.  Also, as the Hayes & Menzel paper shows, it is quite easy 
to create slight variants of FOL that allow for predicates as arguments 
to other predicates. Further, as the Fikes McGuinness axiomatization 
shows, this can be quite easily mapped into a very traditional FOL.

 Therefore, I humbly submit that allowing predicates & classes as 
arguments to arbitrary predicates does not take us into dangerous 
territory. This decision (whether to allow such constructs or not) 
should, in my opinion, be based solely on their utility to the semantic 
web. We should probably do a survey of some sort to collect examples 
where folks have made use of or plan to make use of this feature.

guha

Ian Horrocks wrote:

>First point:
>
>Why we suddenly obsessed with DLs? As I have mentioned, they are
>nothing more than a particular class of decidable subsets of FOL. The
>ability to treat classes/predicates as arguments to other predicates
>is beyond the ability of ANY subset of (standard) FOL, decidable or
>otherwise.
>
>Second point:
>
>The ability to treat classes/predicates as arguments to other
>predicates is of secondary importance. The crucial thing with RDF is
>that it treats the vocabulary of the language itself as standard
>classes/predicates that can be arguments to other predicates. This is
>beyond the ability of almost all logics. It is relatively harmless for
>a language as weak as RDF, but causes fatal complications when more
>expressive power is added.
>
>Ian
>  
>

Received on Friday, 16 August 2002 01:12:32 UTC