- From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
- Date: Thu, 25 Oct 2001 11:32:13 +0100
- To: Pat Hayes <phayes@ai.uwf.edu>
- Cc: w3c-rdfcore-wg@w3.org
At 06:47 PM 10/24/01 -0500, Pat Hayes wrote: >>But suppose we also had another feature, let's call it reif:Truth, such >>that we can say: >> >> reif:Truth rdf:type rdfs:Class . >> _:stmt rdf:type rdf:Statement . >> _:stmt rdf:subject ex:subj . >> _:stmt rdf:property ex:prop . >> _:stmt rdf:object ex:obj . >>and >> _:stmt rdf:type reif:Truth . >> >>Still, there's nothing special about this, just regular RDF statements. > >OK, though I'm nervous about that 'truth'. It hasn't moved yet, but I'm >ready to swat it. I'm sure you are ;-) >>Now suppose we introduce some new semantics, along the same lines that >>you used for RDF schema, in the form of closure rules: >> >> { _:stmt rdf:type rdf:Statement . >> _:stmt rdf:subject _:s . >> _:stmt rdf:property _:p . >> _:stmt rdf:object _:p . >> _:stmt rdf:type reif:Truth . } >> >>|- >> _:s _:p _:o . >> >>(hoping you'll follow my mixed notations). > >Yeh, well, there is a use/mention shift in there somewhere, but we can do >things like that when stating semantic conditions, I guess. (Wouldn't you >also want this to run backwards, though?) Hmmm... this where I can't match your understanding of this stuff ... I thought the RDF resources here were being kept on the "use" plane. The closest to "mention" I can see is that one *might* claim that the set of five triples somehow "mentions" the statement, but I'm strenuously trying to avoid saying that. (Yes, you're right I would also want it to run backwards.) >> Does this provide us with a basis for making sense of reification? > >That is basically adding a truth-predicate, right? That would give it >considerably greater inferential power, but it still wouldn't handle the >type/token confusion (if it is confusion...). I'm not clear about what exactly is a "truth predicate" -- I had understood it to be something that accepts a statement token (per your recently suggested terminology) and delivers a corresponding truth value. I'm trying to avoid that. As far as I can see, all I've described above can work entirely in the value space. (Hmmm... does that mean I should have used "|=" instead of "|-" when stating the closure rule? I wondered about that when I wrote it.) >PS. Another musing, in reply. Maybe it would be easier to do this kind of >thing in terms of documents rather than triples, along the lines that Jos >and Tim are going with the log#entails stuff. For some value of "document", that works for me. But I wouldn't want a document to necessarily be identified with a web-resource boundary. For example, CC/PP conveys fragments of RDF in transient protocol elements that don't have any existence in the Web as we usually think of it. Also, I think that it would be useful to identify a "sub-document" (sometimes called a "context" or "statement set" by myself and others) for these purposes. > Then a reification of a document would be a (different) document that > described the first one. The point being that documents have URIs, so > they must be tokens, and the uriref provides just the 'missing link' > between a reification and the particular tokenish thing it is supposed to > be a reification OF. Your truth-conditions could then be stated as > conditions on valid entailment between documents, so that any RDF graph > would be reification-equivalent to another one, its reification, which > described all its triples and asserted them to be true. It would have > five times as many triples (but hey, what are you gonna do without > universal quantifiers?) Or, we could also allow one document to assert > another, and then we would have two documents: the reification document > with 4n triples in it, and the assertion document with one triple in it > that just says that the reification document is true. Then the assertion > document is reification-equivalent to the original document just in case > the reification document accurately reifies it. Yes, any/all of that seems fair enough to me (and maybe some variations can be imagined by adding some additional semantic "closure" rules). I would guess the conditions of valid entailment between documents would need to appeal to something similar at the statement level. If I were implementing this stuff (and I do plan to do something like this), I'd use an optimized storage form to contain the triple-bloat. But I'd see that as an optimization with a well-defined correspondence to RDF form, not an alternative syntax for an alternative RDF. #g ------------------------------------------------------------ Graham Klyne MIMEsweeper Group Strategic Research <http://www.mimesweeper.com> <Graham.Klyne@MIMEsweeper.com> ------------------------------------------------------------
Received on Thursday, 25 October 2001 12:33:56 UTC