- From: Graham Klyne <Graham.Klyne@Baltimore.com>
- Date: Wed, 05 Sep 2001 11:23:01 +0100
- To: pat hayes <phayes@ai.uwf.edu>
- Cc: Aaron Swartz <aswartz@upclink.com>, w3c-rdfcore-wg@w3.org
At 12:13 PM 9/4/01 -0700, pat hayes wrote: >>I think that princeNodes should be allowed in the predicate slot... >>they're rather useful. >> >>While I'm giving unsolicited advice, I think that a DLG is probably not >>the best way to represent the RDF model... it's sort of difficult to >>picture arrows pointing at other arrows. > >If *that* is allowed then the M&S is totally screwed up. Is it legal RDF >to have a property be the value of another property?? This is something that I have found intuitively "easy" but difficult to explain clearly. My intuition is that an arc is somehow associated with a property node, but that different arcs with the same property label are still different arcs. (The programmer in me might say that an arc is an instance of a type described by the property.) But this is inadequate as a formal explanation... Turning to the MT document for guidance (28-Aug-01 draft, section 0, penultimate para). We have one node for each uriref, anonNode or qLiteral in the document, and one edge for each triple. But what about the urirefs that are used to identify properties? This seems to be a problem with the description as given. It seems to me that there is a difference in the treatment of URIs used to label nodes and URIs used to label arcs, but I'm not sure how that is formalized. I used to think of reification as providing a way to create an effect that might have a graph syntax of an arc pointing to/from another arc. In any case, I think it's certainly possible to have the uri that labels a property arc also be used to label a node that is the subject and/or object of another property, which some might say is "to have a property be the value of another property". So my points are: (1) I think the MT text about URIs in graphs may need refining. (2) My answer to your question is "maybe, yes". ... Should arcs be allowed to be "princeNodes"? I note that allowing property arcs to be "princeNodes" is not the same as having ordinary nodes be princeNodes. A URI denotes a node resource, but it is an attribute of a property arc. How does a formalization capture this kind of distinction? I have also found that to describe RDF-schema-based inferences, I have wanted to construct expressions in which the RDF property is a "variable". I think the required effect could be achieved by means other than "princeNode" arcs, but maybe less intuitive for a developer. (Hmmm... are we finding out why CGs use bipartite graphs rather than labelled arcs?) #g ------------------------------------------------------------ Graham Klyne Baltimore Technologies Strategic Research Content Security Group <Graham.Klyne@Baltimore.com> <http://www.mimesweeper.com> <http://www.baltimore.com> ------------------------------------------------------------
Received on Wednesday, 5 September 2001 07:06:38 UTC