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From: Stian Soiland-Reyes <soiland-reyes@manchester.ac.uk>
Date: Mon, 23 Jan 2017 10:56:14 +0000
Message-ID: <20170123105614.GB2045@biggiebuntu.localdomain>
To: W3C RDFa Community <public-rdfa@w3.org>, "public-rdf-comments@w3.org" <public-rdf-comments@w3.org>
On Sun, 22 Jan 2017 22:28:47 -0600, Pat Hayes <phayes@ihmc.us> wrote:
> I may not be following this discussion properly, but surely it was always
> part of the RDF vision, from the beginning, that RDF content, ie RDF graphs,
> from various sources can be combined and used in reasoning. (If not, what is
> the point of the entire semantic web vision?) So it seems to me to be a
> reasonable extrapolation that if AAA and BBB are two surface syntaxes *for
> describing RDF graphs*, then the fact that they are different surface syntax
> should not be interpreted as carrying the implication that the RDF content
> they encode should not be combined into a single RDF graph (however that
> graph is encoded.) The combination RDFa+JSON-LD reads to me as just a dialect
> for RDF+RDF. 

I think the main questions in this situation are:

1) Do the 'subdocuments' (each RDF block) have to be semantically

2) Can blank node identifiers be shared across RDF blocks and syntaxes?

I think as HTML as a container of multiple RDF representations has
not not been specified, the safest would be to assume each block is a separate
RDF subdocument (parsed separately), and do not share blank node identifiers.

(you can easily imagine RDFa content and JSON-LD content being generated
through quite different code bases and therefore might accidentally share bnode

However all of these would have the same document URI as the base URI - and
be from the same authority (usually the base URI), so it would be weird if they
were NOT semantically consistent. So I would say they should be semantically
consistent and thus mergable to a single graph - given that you avoid bnode
overlap when merging.  

This is equivalent to retrieving the same URI with different content
negotiation, which should yield semantically consistent (if not the same)

I think RDFa+JSON-LD should be the same as JSON-LD+JSON-LD, as each JSON-LD
block must be parsed separately (eg. they can't share @context) - however RDFa
is a single resource across the whole HTML document (but not inside iframes).

So my view is that these 3 blocks each describe *different* RDF resources
(unless told otherwise through sameAs etc):

    <script type="application/ld+json">
        { "@id": "_:b1",
          "@type": "http://schema.org/Person",
          "http://schema.org/name": "Jamie Oliver" }      

      <div vocab="http://schema.org/">
        <p typeof="Book" about="_:b1">The 
          <strong property="name">Jamie Oliver</strong> biography.</p>

      <script type="application/ld+json">
        { "@id": "_:b1",
          "@type": "http://schema.org/Restaurant",
          "http://schema.org/name": "Jamie Oliver" }

(because each _:b1 is parsed separately)

..but they should still be semantically consistent (composable in a single
graph), e.g. not have incompatible types for a resource with the same
absolute URI.

As JSON-LD can described named and unnamed @graphs these would be similarly
mergable to a single RDF Dataset, as if loaded from multiple .jsonld files.
(RDFa does not have a way to do named graphs)

Stian Soiland-Reyes
University of Manchester
Received on Monday, 23 January 2017 10:56:46 UTC

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