- From: Graham Klyne <Graham.Klyne@Baltimore.com>
- Date: Wed, 25 Jul 2001 09:57:11 -0400 (EDT)
- To: Brian McBride <bwm@hplb.hpl.hp.com>
- Cc: RDF core WG <w3c-rdfcore-wg@w3.org>
At 11:31 PM 7/23/01 +0100, Brian McBride wrote: >Graham Klyne wrote: > > > I think the assumption that the URI denotes a specific resource is somewhat > > empty if one has no other knowledge about the resource thus denoted. As > > Pat pointed out, in this situation you can do no more than infer that such > > a resource exists. > >If I use that resource twice, in one case I'd expect to use the same resource >twice, in the other, I could not have that expectation. (When you say "If I use that resource twice" I assume you mean "use that URI twice"?) Indeed. This is something that using a locally quantified variable name or a skolem-constant-like-name makes possible that is not possible using un-named resources. In the XML syntax, several statements may be syntactically grouped to refer to the same un-named resource. When translated to (say) N-triples that syntactic grouping is no longer available so some form of identifier must be provided. Obvious stuff, maybe. I think that, either way (i.e. using an existentially quantified variable or a skolem-constant-like identifier), generated identifiers from different documents (or unrelated parts of the same document) cannot be assumed to be the same resource though the possibility of them refering to the same thing cannot be excluded. I.e. we don't know if they're the same or different by virtue of the form of labelling used. > > > > > o provenance: when a source of rdf states some properties about > > > a resource named by a URI it is making assertions that the > > > resource named by that URI has those properties. when a source > > > of rdf states properties about a variable, it is making no > > > assertions about the name of that resource. > > > > The detailed form of the argument here depends a bit on whether one assumes > > that URIs:resources are 1:1, or if several URIs can identify the same > > resource. But either way I assert that two URIs can ultimately refer to > > the same thing in the domain of interpretation. Thus, assertions about a > > resource named by a uniquely-generated URI MAY be referring to a resource > > that is elsewhere known by a specified URI. This seems to be the same as > > information that one has about a resource identified by a variable. > >A sends signed rdf containing anon node to B. It matters whether A or B >generates the URI. If B generates it, A has not signed that name->resource >mapping. Indeed, but what's in the name? The signature provides some assurance about some entity that is denoted by a named used in the signed document. The signature value itself depends on the name used, but the assurances conveyed do not. I see three possible cases: (a) Signature over a document containing a locally scoped variable (b) Signature over a document containing a generated URI about which we are guaranteed to have no other information. (c) Signature over a document containing an elsewhere-defined URI about which we may have some other information. I think the assurance conveyed by the signature in cases (a) and (b) is indistinguishable. In all cases, the name-to-some-resource binding *is* signed, but only in case (c) may we have any additional knowledge of the bound resource. #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, 25 July 2001 11:23:53 UTC