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

Re: Implementing statement grouping, contexts, quads and scopes (was: Re: Out of context, in context, out of subject ????)

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Mon, 24 Jun 2002 13:24:50 +0300
To: <areggiori@webweaving.org>
CC: RDF Interest <www-rdf-interest@w3.org>, RDF Logic <www-rdf-logic@w3.org>
Message-ID: <B93CCE22.173FD%patrick.stickler@nokia.com>

On 2002-06-24 12:44, "ext Alberto Reggiori" <areggiori@webweaving.org>

> Patrick Stickler wrote:
>> 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.
> which you can even try to express in XML/RDF syntax as:
> ...

Well, sure, if you're in a really masochistic mood ;-)

However one expresses and executes the above rule to
"activate" layer specific assertions is really beside
the point. What matters is that it can be done automatically
and generically, and applications operating at layers
below can safely ignore the unasserted statements.

> IMO what's needed instead is the possibility to make some parsing rules
> optionals
> i.e. optional reification; the syntax could be in principle left un-touched.
> Of
> course, all this "optionals" can be somehow coded the application self by
> triggering some retract() triple methods on useless triples i.e. do not change
> existing software ;-)

But this doesn't work well in practice, because in order to "retract"
triples *below* a given layer one must then have apriori knowledge
about the vocabulary used by each *upper* layer, which is the wrong way

Lower layers should not have to know about higher layers. By simply
using reification as presently defined, and leaving it up to each
higher layer to "activate" the statements relevant at that higher
layer, the lower layers can remain happily ignorant.

(and yes, you get all this "for free", since RDF already provides
the reification machinery -- even aside from the proposed contracted


Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Monday, 24 June 2002 06:20:23 UTC

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