- From: Graham Klyne <GK@Dial.pipex.com>
- Date: Thu, 14 Sep 2000 23:51:49 +0100
- To: "McBride, Brian" <bwm@hplb.hpl.hp.com>
- Cc: "'RDF Interest (E-mail)'" <www-rdf-interest@w3.org>

At 10:10 PM 9/14/00 +0100, McBride, Brian wrote: [...] > > I > > think I am > > forced to conclude that it represents an *extension* to the > > RDF model as > > defined. > >That may well be :( > > > Specifically, the "mapping called Reification" is a > > new concept > > that is not present in the original, and the only way to find > > that mapping > > using the original model is to find the set of 4 statements > > that comprise > > the reification. > >Please forgive my stupidity, but I don't follow the argument. >M&S does have the idea that a reified statement is represented >by a resource. I think the mapping called Reification is a >component of the abstract model described by m&s. I think it >can be positioned as a clarification of what is already >defined. I agree that M&S has the concept of a reified statement represented by a resource. My view is that the _mapping_ -- the function or relation that associates the resource representing a reified statement with the actual statement it represents -- is not there. Consider, if you have an RDF model (per M&S section 5 formal model) containing: [A] --type------> [Statement] [A] --subject---> [S] [A] --property--> [P] [A] --object----> [O] [B] --type------> [Statement] [B] --subject---> [S] [B] --property--> [P] [B] --object----> [O] [S] --P---------> [O] There is no way to know if [A] or [B] is the reification of "[S] --P--> [O]". Thus, I suggest the formal model does not contain the information needed to construct the mapping you describe. (However it could be said that either [A] or [B] reifies the statement "[S] --P--> [O]".) >I suspect my problem is that we are thinking in different modes. >For me, as a mathematical abstraction it can work as defined. >I'm thinking of abstract model here, not of implementation. > >Maybe you could spell out the problem for me. Let me also take a stab from a mathematical abstraction PoV. IIRC, a mapping from some domain {d[i] in D} to some range {r[j] in R} is defined a set of pairs { <d[ik],r[jk]> } that defines the mapping correspondence between members of D and R. It is this set of pairs that is absent in the formal RDF model. >Let me go through briefly the results of a conversation with a >colleague of mine. Stuart asked me what would the semantics of >an incomplete reification be. I think the answer hangs together >reasonably well and may be useful to this discussion. Sure, I think it hangs together just fine. [...] >If we apply the same thinking to reification, and I'm assuming >here that the resource modeling the reified statement is >anonymous, then given a set of statements like: > > S = anon:S > { > (S, [rdf:type], [rdf:Statement]), > (S, [rdfs:subject], [http://aldbaran.hpl.hp.com/bwm]), > (S, [foo:assertedBy, "Graham") > } > >This is a statement about an incomplete reification of a >statement. What does it 'mean'. Informally, using the same >reasoning as above, its semantics would be "Graham has >made a statement about my internal HP homepage", but it >doesn't say exactly what statement. > >That's the intiution. What do you think? If it stands up >to initial scrutiny, I'll maybe have a go at expressing >it in a more formal language. It seems plausible to me. My only reservation is that it introduces a new type of symbol into the formal model (anon:S doesn't really work as a URI, I think). But I think that may be handled in other ways while retaining your basic approach to partial reification. I'm not sure why you feel you need the _mapping_ between statements and reifications. #g ------------ Graham Klyne (GK@ACM.ORG)

Received on Thursday, 14 September 2000 19:26:14 UTC