- From: Andy Seaborne <andy.seaborne@epimorphics.com>
- Date: Fri, 15 Jun 2012 08:50:18 +0100
- To: RDF-WG <public-rdf-wg@w3.org>, public-linked-json@w3.org
(where emails replies go to needs sorting out) >>> Question 2: My understanding is that >>> >>> { >>> "@context" : ... >>> "@graph" : ... >>> } >>> >>> (without @id) defines triples into the default graph. Which also means that if I have a nested situation of the sort: >>> >>> { >>> "@context" : ... >>> "@id" : URI >>> "@graph: { >>> "a" : "b", >>> "@graph" : { >>> "q" : "r" >>> } >>> } >>> } >>> >>> translates into >>> >>> URI { >>> "a" : "b" >>> } >>> { >>> "q" : "r" >>> } >>> >>> Is that correct? >> This is certainly not intended usage, as @graph evolved from a desire to be able to define multiple top-level entities (subject definitions) where an array would otherwise be used. >> >> However, this can be interpreted by the processor to generate quads. Basically, the [a,b] tuple belongs to an anonymous entity (blank node subject), which is in the graph denoted by URI. The [q, r] tuple also belongs to an anonymous entity (with a different BNode) in a named graph denoted by the BNode of the including entity. (JSON-LD syntax allows the use of BNodes for graph names, even though it might not result in valid RDF). >> >> If you run a cleaned up example through the playground, you can see the Quads which are emitted: >> >> { >> "@context" : {"a": "http://foo/a", "q": "http://foo/q", "URI": "http://URI"}, >> "@id" : "URI", >> "@graph": { >> "a" : "b", >> "@graph" : { >> "q" : "r" >> } >> } >> } >> >> _:t0 <http://foo/a> "b" <http://URI> . >> _:t1 <http://foo/q> "r" _:t0 . >> >> > Well, to be honest, I am actually lost (and that shows either that I am stupid, or that the section seems to be half baked, or both...) and I am not 100% sure how the @graph syntax works. Just to make it very clear, how would you encode a simple TriG thing: > > { > <a> <b> <c> . > } > <URI> { > <p> <q> <r> . > } > > I see where I did make some mistake, but I also do not fully grasp, out of the description, what the 'value' of the "@graph" really is, and on what does "@id" applies in that case. > > Note that TriG, as it stands, does not allow nested graphs, ie, > > <URI> { > <a> <b> <c> . > <URI1> { > <p> <q> <r> . > } > } > > is not accepted. (There was some discussion about nested named graphs in the group, and the agreement is that there is no strong enough use case to go there.) I wonder whether JSON-LD should not take the simple approach to adopt the same principle for now, just to simplify matters (just raising this, not sure yet myself). > > Also, as far as I remember, there is currently an open issue (not necessarily a formal one) whether a Graph ID can be a blank node or not. But do not trust my memory, I am too old for that... > > FWIW: In SPARQL Update INSERT DATA { GRAPH <U> { <s> <p> <o> GRAPH <V> { <s1> <p1> <o1> } } } is a syntax error - GRAPH can only at the top level of the data block. In SPARQL Query, in a pattern, GRAPH <U> { <s> <p> <o> GRAPH <V> { <s1> <p1> <o1> } } or in the algebra: (graph <U> (join (bgp (triple <s> <p> <o>)) (graph <V> (bgp (triple <s1> <p1> <o1>)) ))) i.e. the inner graph <V> is matched against the dataset, and is not related to contents of <U> Andy
Received on Friday, 15 June 2012 07:50:57 UTC