- From: Frank Manola <fmanola@mitre.org>
- Date: Wed, 24 Oct 2001 13:52:24 -0400
- To: Brian McBride <bwm@hplb.hpl.hp.com>
- CC: Pat Hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org
Brian-- It's not clear to me what distinguishing "statement" and "triple" accomplishes in this context. Are we doing "uses" and "mentions" again? The M&S (Section 5) says: "(P162) There is a set called Statements, each element of which is a triple of the form (P163) {pred, sub, obj}" I naturally read that as saying that the triples were statements as far as RDF was concerned (if they weren't, why wasn't the set called "Triples" instead of "Statements"?). Morever: "(P179) From the standpoint of an RDF processor, facts (that is, statements) are triples that are members of Statements." I'd agree that the M&S is not a canonical example of precise language, but as long as we're talking about what the M&S says (or seems to say!), it seems to say to me that triples are statements. Regarding the graph representation: "(P165) We can view a set of statements (members of Statements) as a directed labeled graph: each resource and literal is a vertex; a triple {p, s, o} is an arc from s to o, labeled by p. " This says a triple is an arc in the graph. So if a triple is a statement (by my reading), then an arc is a statement. Maybe some more elaboration would help. When you say: > If I write: > > > > <:sky> <:is> <:blue> . > > <:sky> <:is> <:blue> . > > > > I clearly have two triples. Do you? Or do you have two lines of structured text that represent the same triple? The same problem exists with "tuples". You said: > > o a statement is an abstraction; its a tuple with three components, subject, If distinct tuples are identified by three distinct components, then however many times I write the same three components down, I've still stated only one tuple. Is a triple identified only by its components, or by something else too? If I say "Frank is confused" 500 times, have I made 500 (true) statements, or only one? --Frank Brian McBride wrote: > > Pat Hayes wrote: > > >> Just checking we are clear what is being renamed. > > > > > > Well, I thought I was clear, but now I am completely confused. > > > >> M&S uses the term predicate for a component of a statement. > > > > > > That means a triple, right? Or a [node/edge/node] combination in an RDF > > graph. Or does 'statement' mean something else? Right now, as I > > understand it, there are triples in Ntriples, pieces of graph in the > > graph syntax, and more complicated pieces of syntax in RDF/XML. Which of > > these is called a statement? > > You have put your finger on a key question, that I think we need to get clear if > we are to reconcile the language of the old M&S with the new model theory. > > We are dealing here with two formal models. M&S has a formal model, and we have > the new model theory. I think that M&S has the concept of statement and the new > model theory does not. > > My *personal* reading of M&S is that statement and triple meant two different > things. > > o a statement is an abstraction; its a tuple with three components, subject, > ... > > o a triple is a concrete representation of a statement, e.g. state in a > computer memory, markings on paper etc. > > [I'm not defending this model; I'm just trying to express it. It may well be > full of contradictions] > > How do these concepts relate to the new model theory. Well, a triple in > n-triples is pretty clearly still a triple. What is an arc in a graph? Not a > statement, I think. If I write: > > <:sky> <:is> <:blue> . > <:sky> <:is> <:blue> . > > I clearly have two triples. I would also have two arcs in one of your graphs > (until it got tidied). But to M&S, (as I interpret it, others would disagree) > there is only one statement, because both triples denote the same statement. > > I find no concept similar to statement in the new model theory. > > Brian -- Frank Manola The MITRE Corporation 202 Burlington Road, MS A345 Bedford, MA 01730-1420 mailto:fmanola@mitre.org voice: 781-271-8147 FAX: 781-271-8752
Received on Wednesday, 24 October 2001 13:57:11 UTC