- From: Jeremy Carroll <jeremy@topquadrant.com>
- Date: Thu, 29 Sep 2011 09:39:40 -0700
- To: public-rdf-wg@w3.org
For me, I always understood the graph name as identifying the graph in the model theoretic sense, and find the use of <http://example.org/alice> to identify both the graph and some, presumably difference, resource within the model of the graph as dubious In particular, I feel that is should be possible to introduce vocab like eg:subGraphOf that can be evaluated by comparing named graphs .... (well modulo blank nodes, so maybe eg:isomorphicToASubGraphOf would be more accurate) My understanding predates SPARQL Datasets, and I do not believe that such considerations were important to that WG. Jeremy On 9/29/2011 8:31 AM, Pierre-Antoine Champin wrote: > Hi all, > > as Richard asked me during the telecon of 09-29, I'll try to pinpoint > what bothers me in the SPARQL DATASET proposal. > (this is part 2: part 1 was about the default graph, see other mail) > > One such point is the relation between named graphs and their URI (or > IRI, for that matter). > > SPARQL states that: >> An RDF Dataset comprises one graph, the default graph, which does >> not have a name, and zero or more named graphs, where each named >> graph is identified by an IRI. > On the other hand, RDF Concepts states that: >> An IRI (...) used as a node identifies what that node represents. > You can rephrase those sentences, respectively as: > * a IRI identifies a named graph > * a IRI identifies a resource > > My problem here is that the word "identifies" has a completely different > meaning in those sentences. Indeed, the following is, I think, a usual > pattern in SPARQL (using Trig to represent the named graph): > > <http://example.org/alice> > { > <http://example.org/alice> > a foaf:Person ; > foaf:name "Alice" ; > foaf:mbox<mailto:alice@work.example.org> . > } > > Obviously,<http://example.org/alice> does not "identify" a graph and a > person in the same way. > > I see two ways out of this problem: > > 1) either we force the IRI of a named graph to actually *name* that > graph (in the model theoretic way), but we then depart from SPARQL > DATASETs and widespread use; > > 2) or we rephrase the DATASET definition and make it very clear the the > named graph IRI is a mere label, and not an *name* in the model > theoretic sense. > > What still bothers me with the option 2) is that, in SPARQL or Trig, > those graph labels are syntactically homogeneous to an IRI *node*. > > To illustrates why it bothers me, let me just propose the two following > statements: > > _:a_graph ns:label<http://example.org/alice> . > > vs. > > _:a_graph ns:label "http://example.org/alice" . > > So I would argue that, in the end of the day, neither of the following > sentence is accurate: > > a named graph is identified by an IRI > a named graph is labeled by an IRI > > but in fact: > > a named graph is labelled by a resource > > I'm not saying this is bad, I'm just saying this is where we are aiming > with the second option 2), and we should carefully weight the consequences. > > (imagine for example a owl:sameAs statement between two graphs IRI in a > SPARQL engine supporting OWL inference; what would that mean?) > > pa >
Received on Thursday, 29 September 2011 16:40:06 UTC