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RE: Summary of the QName to URI Mapping Problem

From: <Patrick.Stickler@nokia.com>
Date: Wed, 29 Aug 2001 09:37:18 +0300
Message-ID: <2BF0AD29BC31FE46B78877321144043114BFB5@trebe003.NOE.Nokia.com>
To: phayes@ai.uwf.edu
Cc: www-rdf-logic@w3.org

> >Semantics
> >is of course is issue of perspective. What is semantics at one level
> >is just machinery at another.
> I couldn't disagree more. My entire professional career has been 
> devoted to showing why this false. I think that you are using 
> 'semantics' in an informal sense which is almost certainly 
> insufficiently precise to support the infrastructure being envisioned 
> for the SW.

Perhaps you could do me a favor. It is my understanding that e.g. HTTP 
URI scheme semantics applicable to the structural components of an 'http:' 
URL are irrelevant and invisible to an RDF processor which is using that URI
as the identity of a resource within an RDF graph, and in fact, within RDF 
space, that URI is used as an opaque symbol to which is attached semantics 
which is disjunct from any semantics meaningful to or associated with the 
URI Scheme of the URI, such as the semantics of an 'http:' URL.

Now, we have here two functional layers: RDF, and HTTP. A SW agent
may interact with that URI at either level, and the semantics at
one level does not have significance at the other. When applying
some axiom or inferring some relation, the HTTP semantics are totally
irrelevant. When dereferencing that URI for perhaps some auxilliary
knowledge, the semantics that is defined for the URI in RDF-space is 
irrelevant to the HTTP server.

Now, if my understanding of the division of semantics between functional
layers in such a context is incorrect, I would very much appreciate
understanding why.

My discussion of semantic layers was specifically focused on the fact
that if a QName in an XML serialization is mapped to a QName URI (not
a URI following the URI Scheme of the namespace URI, as is now the case),
the structure of the original XML QName remains explicitly defined in the 
resultant QName URI, and hence QName semantics can be applied without
to that URI if and as needed; yet even though the URI Scheme maintains
the QName structure and hence "preserves" the validity of QName semantics,
that QName URI does *not* introduce QName semantics into RDF, since all URIs
in RDF are merely opaque identifiers, to which is attached *additional*
semantics, and it is only that additional semantics at the RDF level
that is relevant to RDF and RDF based tools operating within the realm
of the RDF conceptual graph. 

I.e. No URI Scheme can introduce any semantics into RDF. The use of any
URI Scheme for resource URIs has no relevance whatsoever to semantics
associated with an RDF graph. Right?

Secondly, I was referring mostly to semantics associated with ontologies
and identified by both URIs in the graph and QNames in serializations,
and not the semantics of RDF itself -- which I see as yet a third
of semantics that is disjunct from either URI Scheme semantics or specific
ontological semantics. 

I.e. The semantics associated with a particular ontology which is
by and processed according to the RDF conceptual model does not add to the
semantics of the RDF conceptual model, and visa versa. Both are needed, but
depending on perspective and the level at which a given operation is being
performed, one or the other may be irrelevant. The semantics that defines
a resource is, or what a statement is, or the relation subPropertyOf, is in
no way dependent on, nor modifies in any way the semantics associated with
a given URI. No? Or have I just headed off to la la land?

I will happily and humbly admit that my knowledge in such matters is
imperfect and I may very well be using terminology in ways which is
either too informal or even incorrect. My perspective on the matter
is based on implementational experience much more so than theory, and 
therefore may not be sufficiently broad or complete to avoid the adoption of
such misunderstandings.

I look forward to any clarifications that you (or anyone else) would care
to offer.



Patrick Stickler                      Phone:  +358 3 356 0209
Senior Research Scientist             Mobile: +358 50 483 9453
Software Technology Laboratory        Fax:    +358 7180 35409
Nokia Research Center                 Video:  +358 3 356 0209 / 4227
Visiokatu 1, 33720 Tampere, Finland   Email:  patrick.stickler@nokia.com
Received on Wednesday, 29 August 2001 02:37:31 UTC

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