- From: Sandro Hawke <sandro@w3.org>
- Date: Wed, 11 Apr 2012 10:41:54 -0400
- To: Ivan Herman <ivan@w3.org>
- Cc: W3C RDF WG <public-rdf-wg@w3.org>
On Wed, 2012-04-11 at 16:27 +0200, Ivan Herman wrote: > Hi Sandro, > > On Apr 11, 2012, at 16:14 , Sandro Hawke wrote: > > [snip] > > >> > >> > >>> > >>> * I think we want another condition that says a given label can only be > >>> associated with one graph. I'm not sure if we say that in the DS > >>> conditions and in merging, or somehow say it globally. Anyway, it > >>> would be something like: > >>> > >>> all i,j in (1...n): if (ui,Gi) in DS and > >>> (uj,Gj) in DS and > >>> ui = uj > >>> then Gi=Gj. > >>> > >>> > >> > >> Right. This was not necessary before, that is why I used the ∃! in the formula that has now changed. Except that it is not Gi=Gj, but that the two graphs are equivalent (modulo bnodes...). > > > > Just to make sure I understand you, this equivalence is to deal with the > > problem where ig you parse the Turtle document "{} <b> 1; <c> 1" twice, > > you're going to get two DIFFERENT graphs, right? So you're saying Gi > > and Gj aren't the same, but are equivalent in this bnode-renaming way. > > If so, yes, I agree. > > I presume you meant [] and not {}... > > Yes, graph equivalence means that the two graphs may be transformed into one another modulo some bnode renaming magic. > > > > >> As for the global thing: I think the semantics can go as far as saying that if you use the same label to two different graphs, then you get into an inconsistent situation. > >> > >> Looking at the result: at the moment I do not see any value in the rdf:Graph class! Indeed, none of the semantic conditions make use of it (except of course its definition). And because this semantics *is* fairly weak after all, this may be fine. > > > > Maybe you're missing Condition 3? That uses rdf:Graph. > > Yes, but the only thing that condition does is to define what rdf:Graph means. But none of the other condition refer to it; put it another way, all the other conditions are formulated without a reference to the fact that ui is or is not in rdf:Graph. If so, what is the use? > > > > > You could make that a bit stronger, too, making it a biconditional. > > That is, it is also true that I(ui)=Gi implies {ui rdf:type rdf:Graph}. > > Yep, could be done, but does not change what I said... I don't understand. rdf:Graph, just as defined in condition 3, is absolutely necessary for some use cases, like providing the dc:license of a graph. > >> Although... there is still the subgraphing question pending; > > > > I'd call that the partial-vs-complete graph reference question, but, > > yes. This is one of those cases where people are using DWIM semantics, > > 'DWIM' ?? Do What I Mean. That is, people are just using Trig with some semantics in mind and in their code which may not be the same as other people's. But see email sent 5 minutes ago that maybe frames this in an okay way. > > so it's painful to switch to standard semantics. > > > > For clarity, we might want to use some syntax like this for now, inside > > the group: > > > > <u> {= <a> <b> <c> } for complete-graph semantics > > > > read as <u> denotes something which hasGraph <a> <b> <c>. > > > > <u> {+ <a> <b> <c> } for partial-graph semantics. > > > > read as <u> denotes something which hasGraph a graph that includes > > at least the triple <a> <b> <c> > > > > (Earlier I suggested using "..." instead of "+", but that gets > > confused with metasyntax. People use "..." all the time in their > > examples to mean they're leaving out some details of the example.) > > > > (Also, Eric suggesting using +{...}, but putting an equals outside the > > braces has a very different implication.) > > > > > >> also whether we want to syntactically determine the nature of the default graph. > > > > You mean like whether it's the merge of the named graphs or not? > > Yes. This came up reading Tom Baker's examples. The semantics being as it is, whether the default graph is the union of all the graphs or not makes a major difference. Maybe in Trig, if there is no default graph, it's the merge. If you want an empty default graph, you have to say "{}". -- Sandro > Ivan > > > > > -- Sandro > > > >> Ivan > >> > >>> > >>> That's it for now... > >>> > >>> -- Sandro > >>> > >>> > >>> > >> > >> > >> ---- > >> Ivan Herman, W3C Semantic Web Activity Lead > >> Home: http://www.w3.org/People/Ivan/ > >> mobile: +31-641044153 > >> FOAF: http://www.ivan-herman.net/foaf.rdf > >> > >> > >> > >> > >> > > > > > > > ---- > Ivan Herman, W3C Semantic Web Activity Lead > Home: http://www.w3.org/People/Ivan/ > mobile: +31-641044153 > FOAF: http://www.ivan-herman.net/foaf.rdf > > > > >
Received on Wednesday, 11 April 2012 14:42:06 UTC