- From: Wolfgang Nejdl <nejdl@kbs.uni-hannover.de>
- Date: Fri, 28 Sep 2001 23:50:50 +0200
- To: Pat Hayes <phayes@ai.uwf.edu>
- cc: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, www-rdf-logic@w3.org
> >From: Pat Hayes <phayes@ai.uwf.edu> > >Subject: Re: model theory for RDF/S > >Date: Thu, 27 Sep 2001 19:42:28 -0500 > > > >> But why bother with all this? The concept of a labelled graph is > >> standard and uncontroversial, so this is one place where we can say > >> some mathematics in a reasonably intuitive way without sacrificing > >> either precision or readability by non-mathematicians. > > > >I am aware of at least four versions of labeled directed graphs. (This > >ignores hypergraphs.) These different versions of labeled graphs differ on > >how they treat edges, and have different implications for the RDF model > >theory. ... > > OK, I agree that this needs to be clarified. (I definitely think that > we should avoid multigraphs. The subgraph lemma could be adapted to > this case, but it creates needless complications, and makes it very > hard to draw pictures.) > > Ive checked several web sources of references, by the way, and found, > amusingly enough, that they often *describe* graphs in a way that > suggests the many-edges interpretation, but give formal results and > definitions that assume the single-edge one (eg assertions that there > are at most n|2 graphs on a set of n vertices), which suggests that > this misunderstanding is quite widespread. > > The possibility of unattached nodes in an RDF graph is quite > interesting. We could take the position that such a node is a simple > assertion of existence, so that each node contains a kind of implicit > assertion of self-identity. This has a nice echo both of CS Peirce > and of the rather curious usage in some W3C documents where a > resource is defined as anything that has an "identity". > Just to compare with related formalisms: O-Telos (and O-Telos-RDF, http://www.kbs.uni-hannover.de/Arbeiten/Publikationen/2001/kcap01_final.pdf) allows these unattached nodes, and treats them as assertions of existence. On the other points mentioned in the preceding discussion: O-Telos/O-Telos-RDF does not make any distinction between literals and other types, and labeled graphs in O-Telos/O-Telos-RDF are single-edge ones (but this is more natural (in contrast to RDF(S)), because instantiated properties (edges) get a new label instead of the name of the property). Wolfgang > But it would be simpler just to make them illegal. > > Pat > -- > --------------------------------------------------------------------- > IHMC (850)434 8903 home > 40 South Alcaniz St. (850)202 4416 office > Pensacola, FL 32501 (850)202 4440 fax > phayes@ai.uwf.edu > http://www.coginst.uwf.edu/~phayes -- Prof. Dr. Wolfgang Nejdl tel. +49 511 762-19710 Institut für Technische Informatik fax. +49 511 762-19712 Rechnergestützte Wissensverarbeitung http://www.kbs.uni-hannover.de/ Educational Technology Lab http://www.etl.uni-hannover.de/ Learning Lab Lower Saxony http://www.learninglab.de/ Universität Hannover, Appelstraße 4, 30167 Hannover, Deutschland
Received on Friday, 28 September 2001 17:53:32 UTC