- From: Jeff Heflin <heflin@cse.lehigh.edu>
- Date: Thu, 23 May 2002 10:49:32 -0400
- To: Tim Berners-Lee <timbl@w3.org>
- CC: www-rdf-logic@w3.org
Tim, I've responsed to a couple of your points below. I hope you don't mind that I've snipped a lot of the original message. Jeff Tim Berners-Lee wrote: > <snip> > > When you use a term (eg Property) in a namespace, its meaning is defined > by the definer of that namespace. You are (unlike in english) > bound to use a term according to its creator's definition. > But how do you know what the creator's definition is? In RDF it is possible to have assertions about the same URI scattered across millions of documents. How can you determine which ones agree with the creator's definition, and which ones don't? Surely, you wouldn't suggest that you ignore everything that's not in the namespace document for that URI? That would severely restrict extensibility. It would mean, among other things, that you couldn't subclass or superclass something defined in another namespace, and as a result, all namespaces would become unrelated islands. <snip> > > This is exactly why RDF as-is is not appropriate for the Semantic Web. > > It really wasn't designed for the problems of a distributed, > > heterogeneous information environment. > > That actually isn't true. It was specifically designed for such an > environment. I believe that it was intended for such an environment, but IMHO it falls well short of those goals. In order to handle a distributed environment, you need more than just "all identifiers will be URIs." You need some way to come up with shared definitions even though global agreement is impossible. To make this machine processable, you need a formal semantics that explicitly takes into account how the distributed axioms used to reason about a set of documents is assembled. Otherwise, different reasoners can conclude wildly different things from the exact same information, providing us absolutely no guarantees about interoperibility. Now I understand that RDF was designed to be a foundation which a lot of things could be eventually built on (I've seen the "layer cake" diagram a million times). However, I think that the distributed nature of the Semantic Web should be a fundamental issue, and not just an "add-on." Furthermore, now that people are beginning to build some of these upper layers, they are finding that RDF is not as easy to extend as they might have wished: the WebOnt WG is already discovering that extending RDF with additional semantics is not a trivial matter.
Received on Thursday, 23 May 2002 10:49:41 UTC