- From: Harry Halpin <hhalpin@ibiblio.org>
- Date: Sat, 25 Sep 2004 19:04:15 -0400 (EDT)
- To: www-rdf-interest@w3.org
- cc: ht@inf.ed.ac.uk
Thanks everyone on this list who discussed the Web Proper Names proposal. A number of questions have been proposed, and the discussion went off to discuss a number of related proposals such as URIQA that have differeing methods for solving the problem of the potential ambiguity between when a URI is used to represent a referent (such as me) or a representation of a referent (such as a webpage). As put by David Menendez, "As I see it, some URIs identify web pages and other identify abstract, non-web-page things". For those interested, I'm going to clarify the options for those wishing to make the distinction (or similar ones, such as that between a resource itself and those representations which it may return). Then I will take leave of what many may consider a philosophical rat-hole, and any further communication with me on this subject should take place via e-mail since I'm sure the www-rdf-interest has more things to discuss at this point: 1) The problem could be solved by using a new URI Scheme, such as the contextualized wpn:// or the less contextualized Larry Masinter tdb:// proposal (http://larry.masinter.net/duri.html). 2) The problem could also be solved by allowing a representation itself to be used to denote a referent, and the Expanded Web Proper Bame format does that with the goal of interoperability in mind. http://www.cogsci.ed.ac.uk/~ht/webpropernames/ 3) Jon Hanna had an RDF schema (rough draft) for distinguishing between resources and representations: http://www.hackcraft.net/rep/rep.xml 4) Thomas Passim had a few RDF predicates that could help: subjectIsTheThingReturnedByThisURI, theDocumentAtThisUriDescribesTheSubject, TheDocumentAtThisUriIsAboutTheSubject - which were not discussed much further, although it's another route. 5) The problem could also be solved by simply grounding a URI in "a RDF graph where the terminal nodes are either URI references, literals, or anonymous nodes not serving as the subject of any statement", which might be even easier with a few new HTTP methods, as suggested by URIQA and Patrick Stickler. ( http://swdev.nokia.com/uriqa/URIQA.html) I tend towards the human-readable representation viewpoint to solve the "URI-grounding" problem, although I find the URIQA model (minus the new http)and the RDF predicate/schema models also interesting avenues. There are definitely some differing views on how URI works. In the ideal semantic web world, at Patrick Stickler put it, "URIs should not be used to denote more than one thing. Period. Only the creator of a URI can say what it denotes." Then, as pointed out, this excludes us from making statements about documents on the Web, especially when the creator does not say what it denotes or I wish to use a human-readable representation to make clear what is being denoted. Phil Dawes suggested "They are solved in the same way as they are solved in real life - using context." WPNs formalize some context, and so do others, and this problem is notoriously hard. You could always, as Graham Klyne points out, use a # at the end to make the differentiation. Jon Black notes that "When a URI denotes, it does so because everyone in a group knows what it denotes", which as he notes is difficult if not impossible in a completely open system such as the SW. Hamish returns to the point of representation, "To humans, being able to dereference a URI and find some explanation of what that URI qua symbol is intended toindicate is very valuable indeed, and I was starting from the assumption that http URIs would be used, as symbols, to indicate non-web resources.", and David Menendez follows "there's no reason that a software agent couldn't do the same." So clearly there's no consensus on this issue and exactly how URIs should be used in the SW - perhaps we can only hope for some Best Practice guidelines from above to clarify the issue, or see empirically how it works in the coming months and years. Again, I would say interoperability between any type of ontology or metadata is going to be difficult, especially where the semantics are unclear, humans may not be too careful about their use of statements (or worse, machines making statements automatically!), and so on. The URIQA proposal has an algorithm for grounding RDF in other RDF, while the WPN proposal could ground RDF statements in human-readable representations that are easy to build and compare. So one could clarify a statement given in FOAF such as: <foaf:image rdf:about="http://www.ibiblio.org/hhalpin/homepage/images/harrytrain.png"> <foaf:depicts rdf:resource="http://www.ibiblio.org/hhalpin.wpn"/> </foaf:image> Where http://www.ibiblio.org/hhalpin.wpn is a google on myself where I've verified and collected useful web-pages with info about me on them, collating them into a EWPN. We'll revise WPN a bit when we have some working code and have fully digested all the comments we have received. And as pointed out by the "OWL and the Real World" discussion, this is difficult going...but rewarding, since I think these types of proposals show how a SW might communicate and grow, and as we put it, to avoid the "real risk that the Semantic Web will consist of a vast number of self-consistent but mutually incommensurable collections of metadata." thanks everyone, -harry
Received on Saturday, 25 September 2004 23:04:16 UTC