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RE: Blank nodes as predicates [was Re: Input needed from RDF group on JSON-LD skolemization]

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Sat, 13 Jul 2013 20:23:50 +0200
To: <public-linked-json@w3.org>
Message-ID: <013601ce7ff6$20647560$612d6020$@lanthaler@gmx.net>
On Saturday, July 13, 2013 12:41 AM, David Booth wrote:
> On 07/12/2013 06:18 AM, Markus Lanthaler wrote:
> > On Friday, July 12, 2013 5:00 AM, David Booth wrote:
> >> On 07/10/2013 10:18 AM, Markus Lanthaler wrote:
> >>> What if I would have some (out-of-band) knowledge that tells me
> >>> that
> >>>
> >>>     _:b2 rdfs:subPropertyOf
<http://example.com/someTheClientUnderstands1> .
> >>>     _:b2 rdfs:subPropertyOf
<http://example.com/someTheClientUnderstands2> .
> >>
> >> It is not possible in RDF to do that, because the blank node label _:b2
> >> has no meaning outside of the original graph.  There is no way, from
> >> outside of that graph, to refer to _:b2 by name.  It has no name
> >> outside of the original graph.
> >
> > Since I am the client and I have out-of-band knowledge and I am the one
> > processing the graph I can simply inject that knowledge into the graph
> > before processing it. So it's certainly possible. How could someone
> > prevent that?
> If you are using standard tools then there is no way to inject a
> statement about _:b2 into the graph before processing it, because _:b2
> has no name that you can reference.  A standard JSON-LD extended-RDF
> parser would take JSON-LD as input and produce extended RDF like this:
>        ...
>        [] [] true .
>        [] [] false .

In JSON-LD there's no way to have a property mapped to an unlabeled blank
node. If you map it to a blank node, it will be mapped to a blank node

> The only way, using standard tools, that you could inject the above
> out-of-band knowledge would be to modify the *original* JSON document to
> inject additional JSON properties that would end up being converted to
> RDF using the same blank nodes. 

Why's that a problem?

> In other words, you would have to: (a)
> parse the document as pure JSON; (b) augment that JSON with your
> out-of-band information;> (c) serialize back to JSON; and finally (d)
> re-parse the result using a JSON-LD extended-RDF parser.

That's trivial in every programming language I know

> That does not sound like an elegant solution.  That sounds like a crude
> hack.


Markus Lanthaler
Received on Saturday, 13 July 2013 18:24:23 UTC

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