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

Re: Implementing statement grouping, contexts, quads and scopes

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 25 Jun 2002 11:46:48 -0500
Message-Id: <p05111b0db93e4be82f5f@[]>
To: areggiori@webweaving.org
Cc: www-rdf-logic@w3.org
>Jonathan Borden wrote:
>>Don't you see what you are trying to do?
>I think I can see what I am trying to do here, which is proposing a 
>practical solution (like Patrick I guess) to layer new semantics on 
>top of RDF using reification and the current XML/RDF syntax which 
>most parsers understand already :-)
>Isn't the WebOnt supposed to layer OWL on top of RDF  using the 
>XML/RDF _as it is today_  [1] or am I missing something here ? :-)
>Can somebody better explain to me what's wrong about using 
>reification for layering ?
>>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
>well, you are right saying that the syntax is ugly, baroque and 
>obese but it is definitively valid XML/RDF :-)
>>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.
>picking up bit and pieces from my previous example, I can define N3 
>formula X as follow:
><rdf:Statement rdf:bagID="X">
>    <rdf:subject rdf:resource="&ex;s" />
>    <rdf:predicate rdf:resource="&ex;p" />
>    <rdf:object rdf:resource="&ex;o" />
><owl:OWLPredicate rdf:about="&ex;p" rdf:bagID="#X"/>
>which does *not* assert (s,p,o) in formula X while
><rdf:Description rdf:about="&ex;s"
>                  rdf:bagID="Y">
>    <ex:p rdf:resource="&ex;o" />
>*does* asserts (s,p,o) in formula (context) Y
>where X=>Y becomes
><rdf:Description rdf:about="#X">
>    <log:imples rdf:resource="#Y"/>
>which is ugly, but if you feed the above into the W3C RDF validator, 
>you get what you expect i.e. X=>Y in triples :)

Well that is very remarkable, since there is no valid way to express 
an implication in RDF triples. log:implies is meaningless in RDF(S), 
please bear in mind.

>>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.
>you might be right here, but I find that the mixture of the two 
>mechanisms working nicely together :)
>>So certainly if you give us a mechanism for N3 formulae the problem would be
>>solved. That is the whole point, really.
>I am not up to speed enough with N3 and rule based systems to say 
>that this is the solution to layering, but I can definitely say that 
>this is *a* solution (or not)

I can definitely say that it is not. Next question?

Pat Hayes

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Received on Tuesday, 25 June 2002 12:46:51 UTC

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