RE: Literals (Re: model theory for RDF/S)

> > ... Or if you like: 'int:5', 
> > 'xsd:float:5.0', and
> > 'foo:intPadTo4:0005', eh?
> 
> This again is fine, but, again, is getting a bit close to retaining
> irrelevant bits.  

I can certainly appreciate having a way to ignore all
of the "irrelevant" bits -- so long as they really are
irrelevant.

> If RDF supports URI schemes that have a 
> built-in notion
> of equality, ...

But again, we can't expect RDF to support every possible
URI scheme and it's particular semantics -- or every known
relation between the semantics of different URI schemes.

At best, RDF could provide generic mechanisms by which 
those URI semantics could be defined and related -- and
in fact, it probably does already, in RDFS (we just don't
have that ontology defined yet).

> > URIs are not themselves the "things" they denote (usually 
> ;-). They are 
> > symbols which denote objects in an explicit symbol system. 
> If two symbols 
> > denote the same object, then, sure, let's define them as 
> equivalent -- but 
> > not at the loss of distinction between the two symbols 
> themselves (as that 
> > distinction may be significant for some operations) -- and again,
> > equivalence
> > may be a contextualized opinion, not a "fact" of the universe.
> 
> OK, now we are getting into the nuts and bolts of systems, 
> not logics.  

Fair enough, but then, I build systems, not logics :-)

> As
> far as (most) logics are concerned, if two symbols denote the 
> same thing,
> then there is no way of determining which one was used, from 
> within the
> logic.

And that's a good thing? Sorry, I probably just
don't have the proper understanding of formal semantics
to follow the "logic" of that (apologies for the awful pun).
 
I guess I'll just have to take your word for it.

> However, it is possible to design a system that 
> allows access to
> several interfaces, one to the logical level and one to the symbolic
> level.  At the logical level, there may be no way of determining which
> symbol is being used, to the point that queries should 
> probably return sets
> of symbols in many cases, and not just single symbols.  At 
> the symbolic
> level, there may indeed be a difference between the two 
> symbols.  There may
> also be other levels, such as a proof-theoretic level, where the
> distinction also makes sense.

Good. And at what level then is the graph itself? Presumably the
symbolic level. And at what level do applications currently
interact with the graph? The symbolic level. And even if one
introduces mechanisms that allow one to equate many nodes to
the same "resource" -- how is that "schitsophrenic" resource
going to be accessed? At the symbolic level.

I guess I'm just not seeing how this works in practice, and
what it means to folks actually interacting with the RDF graph.

I can define rules e.g. in Prolog for equivalentTo, subPropertyOf,
etc. and achieve all kinds of transparent equivalences between
URI identified resources, with no need for all those resources
to constitute the same object/node in the knowledge base.

I guess I just am not following what you would like to see happen.

Do you want, e.g. for nodes in the graph to have multiple URI
lables? Do you want built-in standardized mapping tables of
equivalences -- i.e. move equivalentTo, sub*Of, etc. to have
explicit treatment in the graph itself. 

Forgive my ignorance, or just being slow today. I just don't
follow how such "super-resources" would be realized in the graph.
(forgive a nuts-n-bolts systems engineer for only being able
to see as far as the data structure ;-)

> I agree, except, perhaps, with not placing any of this stuff 
> at the RDF
> layer.  

If putting it at the RDF layer makes my life easier, then I'm 
all for it. I just fear that it will simply overcomplicate
the foundation and reduce the overall flexibility of the
architecture if we end up with an overly heavy graph model,
rather than a ligher graph model and more capable (but
disjuct) functional layers.

> 
> Please read the model theory.  Resource has a particular 
> meaning there.

I'm working on it...  (scary stuff for poor knaves like me ;-)

Regards,

Patrick

--
Patrick Stickler                      Phone:  +358 3 356 0209
Senior Research Scientist             Mobile: +358 50 483 9453
Nokia Research Center                 Fax:    +358 7180 35409
Visiokatu 1, 33720 Tampere, Finland   Email:  patrick.stickler@nokia.com

Received on Wednesday, 3 October 2001 12:31:39 UTC