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RE: Input needed from RDF group on JSON-LD skolemization

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Sun, 16 Jun 2013 13:17:38 +0200
To: "'public-rdf-comments'" <public-rdf-comments@w3.org>
Message-ID: <00bb01ce6a83$1ce3e340$56aba9c0$@lanthaler@gmx.net>
On Saturday, June 15, 2013 7:41 PM, Pat Hayes wrote:
> I do not see any point in using a different suffix. The logic of
> skolemization is the same in both cases. There is no need to 'flag' an
> IRI to prevent it being made back into a bnode in a situation where it
> is in any case illegal to make it into a bnode. I think the use of
> another suffix encoding achieves nothing of value and is likely to
> produce confusion. For example, would it be an error to use a json-ld-
> genid (of gen-genid) skolem ID in a situation where it *would* be legal
> to replace it with a bnode? Therefore I suggest simply using genid for
> these skolemizations just like the others.

I second that but let me ask another question which was the main question
that triggered this thread. The to-RDF algorithm in the JSON-LD
specification currently produces quads which may contain blank node
identifiers in the predicate position. The spec also contains the following

   This algorithms converts a JSON-LD document to an RDF dataset.
   Please note that RDF does not allow a blank node to be used as
   a graph name or property, while JSON-LD does. JSON-LD-RDF
   Converters can work around this restriction, when converting
   JSON-LD to RDF, by converting such blank nodes to IRIs, minting
   new "Skolem IRIs" as per Replacing Blank Nodes with IRIs of

The question is whether skolemization should be required. That would mean
that the algorithm would not emit blank node identifiers in the predicate
position anymore - not even for system that support them.

Our reasoning was that it is simple enough to do skolemization at a layer
above the to-RDF algorithm. As we all know, it is theoretically impossible
to mint *new, globally unique IRIs* - especially if you are a client and not
a server, i.e., if you don't even have a IRI space that "belongs to you". On
the other hand, David argues that skolemization MUST be done to produce
valid RDF and achieve interoperability.

I would like to hear more opinions on that.


Markus Lanthaler
Received on Sunday, 16 June 2013 11:18:07 UTC

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