Re: Example of applying sorted-nucleus? was Re: [TED] CORE Pages on Positive Conditions and Horn Rules Edited: Slots & Constraints

> Michael Kifer wrote:
> 
> >> This was at the heart of why I was confused first time around. To me 
> >> "webizing" is about how you spell things like variable-names and 
> >> procedure-names, and not to do with the type system that constrains the 
> >> types of variables or the signatures of procedures.
> > 
> > I think webizing means the use of IRIs as global identifiers for constants,
> > properties, and concepts. Because the same symbol (IRI) can be used in all
> > these different contexts (and some other symbols, like integers may not be
> > allowed to be used in some contexts), 
> 
> Well the symbol isn't necessarily the bare IRI itself. One could have 
> symbols in which the IRI is but a part of the token so that property:iri 
> and constant:iri could be syntactically distinct symbols, identifiable 
> locally without any recourse to any separate signatures.

Is it for my information or an argument negating something in the above?


>  > it is necessary to have one domain
>  > and also some rules to specify which combos of syntactic elements are
>  > allowed and which are not. This is essentially the main use of
>  > multi-sorted languages.
> 
> Is that necessary?
> 
> In RDF, for example [*], the syntax is very permissive. This is possible 
> because in the model theory a single domain element can be both a 
> constant, a property (have a property extension) and a class (have a 
> class extension) so we avoid having to make any syntactic distinctions 
> at all between those things. When we do have to make syntactic 
> distinctions (specifically, typed literals) they are designed to be 
> self-describing. This permissive, schemaless, self-describing, nature is 
> a key to its value in many of our applications.
> 
> Then for specific applications we create vocabulary elements and define 
> their semantic structure in OWL but all that is at the semantic level 
> and the syntactic language remains common.
> 
> I guess I was hoping for RIF core to be somewhat similar - a general 
> purpose core syntax with few restrictions where dialects introduce 
> symbols with dialect-specific semantics but don't need to modify the 
> language syntax - more like lisp than pascal.

This is exactly what we are doing.  However, not through hand waiving, like
it was done with RDF, but through rigorous, known, and well-defined logical
techniques.

Did you read my previous message to this list? I was hoping that it would
make it clear how things work in the logic.


> I guess the counter argument is that that that might be OK for the core 
> but some dialects will want stronger syntactic constraints and so a 
> syntactic constraint mechanism is needed.
> 
> The counter to that counter is that it is hard to do that in a way that 
> supports forward compatibility.

I don't understand your counter or counter to the counter.
The proposed framework is very general -- much more general than RDF. So, I
fail to see how can it be that RDF allows forward compatibility and RIF
Core doesn't.

RDF doesn't allow forward compatibility, by the way. Just look at the mess
that RDFS has created with OWL-DL/OWL-Full stuff.

> >> I guess this isn't a problem in RDF because the interpretation of foo^A 
> >> and foo^B will be identical - the lexical-to-valuespace map will map 
> >> each onto the same valuespace element - and in RDF it's only the 
> >> interpretation we care about.
> > 
> > Which basically means that RDF has an implicit equality theory in which
> > foo^A = foo^B if A is a subtype of B.  But for an extensible (and much
> > richer) family of rule languages, like RIF, this is not good enough. One
> > needs more general means of specifying sorts and domains.
> 
> I think it is more because this is semantic equality and that's all we 
> care about in RDF, see above discussion. Then we have the full power of 
> OWL for specifying semantic structure such as equality.


What is semantic equality? Please define.


> > In the language one asks questions like "is this particular constant (IRI,
> > for example) a member of the class owl:Thing?" The answer is always yes
> > because every constant is interpreted as a member of the domain of
> > interpretation, and owl:Thing is, by definition, interpreted by the set
> > that equals the entire domain.
> 
> Minor point, but see discussion with Harold, owl:Thing is only the 
> entire domain in the case of OWL/full, for OWL/DL it is a strict subset.

Yes, minor point. But in OWL DL they don't include concepts and roles in
the domain.


> I wonder if the next stage is to find a way to ground this. Can the 
> working group come up with a specific test case of a RIF dialect that 
> needs to extend the core in a simple but somewhat representative way? 
> Then we could work through the details of precisely how that extension 
> is done.


Right. But we haven't defined RIF Core yet.


> Dave
> 
> [*] I realize that RDF is not a primary concern of RIF and that I sound 
> like a broken record on it but (a) it helps me to base the discussion on 
> something I understand which seems to have taken a different course and 
> (b) we are chartered to end up with something somewhat RDF-compatible :-)


It is 100% compatible. I was hoping that my previous email clarified this
completely.


	--michael

Received on Thursday, 14 December 2006 14:18:25 UTC