W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2002

Re: Implementing statement grouping, contexts, quads and scopes

From: Jonathan Borden <jonathan@openhealth.org>
Date: Mon, 24 Jun 2002 11:00:18 -0400
Message-ID: <043b01c21b8f$de8078f0$0a2e249b@nemc.org>
To: "Patrick Stickler" <patrick.stickler@nokia.com>, <areggiori@webweaving.org>, "Didier" <didier@phpapp.org>
Cc: "RDF Interest" <www-rdf-interest@w3.org>, "RDF Logic" <www-rdf-logic@w3.org>

Patrick Stickler wrote:

>
> On 2002-06-24 10:47, "ext Patrick Stickler" <patrick.stickler@nokia.com>
> wrote:
>
> >
> > On 2002-06-21 15:53, "ext Jonathan Borden" <jonathan@openhealth.org>
wrote:
> >
> >> The concept of "dark triples" as a layering option seems to be getting
a bit
> >> misunderstood. The essence of "dark" or "unasserted" triples is simply
that,
> >> from a technical perspective, it is difficult (some would indeed say
> >> impossible) to define a language such as OWL (and given the constraints
> >> placed on this language by the WebOnt charter etc.) in RDF if OWL is to
have
> >> the characteristics we desire, and RDF triples are all "truths".
> >
> > I consider RDF to already have a mechanism for expressing unasserted
> > triples, namely reification. The only reason folks want to create
something
> > else, IMO, is simply because the RDF/XML syntax is so obese. I.e.
> >
> >  <rdf:Statement>
> >     <rdf:subject   rdf:resource="#foo"/>
> >     <rdf:predicate rdf:resource="&owl;bar"/>
> >     <rdf:object    rdf:resource="#bas"/>
> >  </rdf:Statement>

Yes, this syntax is not acceptable for Semantic Web languages that are are
to be 'layered' on RDF.

...
> Note also that unasserted "dark" statements at the RDF-level can be
> asserted at any given higher level where they have meaning in a automated
> and generic fashion.
>
> OWL level assertions can be easily automated using this approach
> by a single rule:
>
> {
>    ?x rdf:type rdf:Statement .
>    ?x rdf:subject ?s .
>    ?x rdf:predicate ?p .
>    ?x rdf:object ?o .
>    ?p rdf:type owl:OWLPredicate .
> }
> log:implies
> {
>    ?s ?p ?o .
> }
>
> Done.
>

Well these sorts of issues and purported solutions appear to be a uniform
characteristic of attempts to develop languages _in_ RDF that are also to be
layered _on_ RDF (e.g. TimBL's "layer cake" as it is called).

Don't you see what you are trying to do?

You are writing an N3 formula _which is not RDF but as if it were something
in RDF_ and casually tossing this out as a solution to some problem _in
OWL_.

How is OWL to use such a formula if OWL is to be layered on RDF? How are
such rules supposed to be specified? Sure if we accept N3 this is no problem
but that's the point: N3 formulas, when represented as triples, use
collections of unasserted triples. This is most basic:

X=> Y

does not imply (i.e. assert) X so you need a way to _say_ "X" without
asserting X.

But hold on and understand this:

You are proposing RDF reification as a way to 'implement' unasserted triples
but you are using _another_ mechanism of unasserted triples in order to
'implement' reification. It is exactly these sorts of arguments that are
akin to trying to develop a perpetual motion machine.

So certainly if you give us a mechanism for N3 formulae the problem would be
solved. That is the whole point, really.

Jonathan
Received on Monday, 24 June 2002 11:05:59 GMT

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