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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
sentence:

   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
   [RDF11-CONCEPTS].

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.


Thanks,
Markus


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

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