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comments/questions on JSON-LD spec (but _not_ for the CG->WG transition!)

From: Ivan Herman <ivan@w3.org>
Date: Thu, 14 Jun 2012 12:29:26 +0200
Cc: Linked JSON <public-linked-json@w3.org>, W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <FF58E5D8-1A76-430F-ACBE-BFB9BA7032F7@w3.org>
To: Manu Sporny <msporny@digitalbazaar.com>, Gregg Kellogg <greggkellogg@gmail.com>
To avoid any kind of misunderstandings: my comment/question should not have a bearing on whether the document comes over to the RDF WG or not, ie, I do not consider that as a prerequisite for starting the whole procedure. Consider it as a comment that may result in active RDF WG issues on the draft either before or after the FPWD publication.

My questions are on the section on @graph, ie, section 4.9 (and tried to look at the API doc, too). They may be clarification issues but maybe missing features in the spec. Obviously, I look at this with an RDF, more exactly RDF Named Graph (put your preferred term here:-) goggle on. I also have some comments on the construct itself, see below.

Question 1: I do not understand the last example in the section, namely the lonely "http://www.markus-lanthaler.com/". There is some text there about additional meta data about Markus, but what would that mean in terms of TriG? Could you describe this? 


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? However, I tried to look at the RDF algorithm in the API document, and I did not see anything about the case when the @id is not set for a @graph. Did I miss something?

Comment 1: I also try to imagine a JSON user who does not know anything about RDF and, obviously, of named graphs either: for that person this construct may be a bit confusing. First of all, such a person may not _really_ think in term of a graph (and the rest of JSON, ie, also the JSON-LD document, cleverly hides this concept). Ie, this keyword might be confusing. Also, the "@graph" : { ... } does not really fit, at least for me, in the mental model of a property-value pairs _on a common subject_, that is the fundamental paradigm in JSON-LD (rightfully so) because it is, somehow, fundamentally different; we are not making statements on the @id value, we are somehow changing the nature of what is happening. I know something is needed at least for the top level objects even if we do not talk about the named graphs (after all, I raised this issue in the past), but I am not convinced about the direction this goes syntax-wise. (Again, this is a discussion on or before the FPWD, _not_ a prerequisite to get the document over to the RDF WG!)

Comment 2: There is, of course, the general question whether it is wise to publish a FPWD with a @graph features as long as the discussion on named graphs is still raging in the group. Maybe that section should be stripped down, for the moment, to the bare minimum that is necessary to express a graph with several top level subjects... But that is just a thought. I know the API values are set in terms of quads but we can say, at this moment, that JSON-LD does not yet have a syntax to express the full quads, only those for a default graph...

Thanks

Ivan

----
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 Thursday, 14 June 2012 10:30:00 GMT

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