- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: 2003年2月19日 13:43:23 -0500 (EST)
- To: GK@ninebynine.org
- Cc: www-rdf-comments@w3.org
- Message-Id: <20030219.134323.27303466.pfps@research.bell-labs.com>
From: Graham Klyne <GK@ninebynine.org> Subject: [RDF-Concepts:109] What is the expressive power of RDF? Date: 2003年2月19日 16:05:36 +0000 > Peter, > > With reference to your comment: > http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0154.html > > I accept a need for editorial revision, and have recorded it with id > 109-ExpressivePower [**]. The purpose of the rest of this message is to > try to ensure that I properly understand your concerns. > > [**] for my own tracking purposes: when the scope of the issue is > established, I'll ask Brian to allocate a WG tracking ID. > > I think the problem can be described thus: > [[ > There is incorrect wording describing the expressive power of RDF. > > A formal description would be: > "The expressive power of RDF is equivalent to the binary > existential-conjunctive subset of first order logic". > > Any informal explanations should be consistent with this. > ]] > > > To further help me understand your concerns, can you clarify to me why you > regard the following representations are not legitimate answers to the > questions you raise: > > [[ > 1. How can > takes(John,book,school) > be represented in RDF? > > <rdf:Description> > <rdf:type rdf:resource="ex:TakingEvent" /> > <ex:taker rdf:resource="ex:John"/> > <ex:taken rdf:resource="ex:Book"/> > <ex:to rdf:resource="ex:School"/> > </rdf:Description> This is an encoding of a trinary relationship as several binary relationships. If you wish to admit such encodings, then I think that you should be much more formal about ``expressive power''. It may be that under some suitable definition of ``expressive power'' RDF can express n-ary relationships. However, under other definitions of ``expressive power'' the above encoding is not admissable. For example, the above encoding allows for TakingEvents that do not have a taker, but the trinary takes predicate does not admit this possibility. > 2. How can > loves(John,spouse(John)) > be represented in RDF? > > <rdf:Description about="ex:John"> > <ex:loves rdf:parseType="resource"> > <rdf:Description> > <ex:spouse rdf:resource="ex:John" /> > </rdf:Description> > </ex:loves> > </rdf:Description> > ]] This is not even an encoding, as it is missing the functionality of spouse. You haven't addressed the second half of this comment. > #g Peter F. Patel-Schneider Bell Labs Research Lucent Technologies > At 10:26 AM 1/30/03 -0500, Peter F. Patel-Schneider wrote: > > > >RDF Concepts states > > The expressive power of RDF corresponds to the > > existential-conjunctive (EC) subset of first order logic [Sowa]. > > > >How can > > takes(John,book,school) > >be represented in RDF? > > > >How can > > loves(John,spouse(John)) > >be represented in RDF? > > > >How can the RDF and RDFS semantic conditions be represented in the > >existential-conjunctive subset of first order logic? > > ------------------- > Graham Klyne > <GK@NineByNine.org>
Received on Wednesday, 19 February 2003 13:43:47 UTC