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

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 15 Jun 2013 12:40:38 -0500
Cc: public-rdf-comments <public-rdf-comments@w3.org>
Message-Id: <7C1AC8AE-55B9-47C0-AA7E-76952B4A2557@ihmc.us>
To: David Booth <david@dbooth.org>

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.


On Jun 13, 2013, at 12:09 PM, David Booth wrote:

> The JSON-LD group would like input from the rest of the RDF Working Group about skolemization.
> During the last JSON-LD call
> http://json-ld.org/minutes/2013-06-11/
> there was discussion of a proposal to require skolemization of JSON-LD blank nodes, when interpreting JSON-LD as RDF, in cases where they otherwise would be converted to RDF blank nodes but are used where a blank node is not allowed in RDF.  (At present they are prohibited as predicates and as graph names.)
> The proposal was #1 at:
> http://lists.w3.org/Archives/Public/public-rdf-comments/2013Jun/0072.html
> [[
> 1. In RDF conversion algorithms in JSON-LD 1.0 Processing Algorithms and
> API,
> http://json-ld.org/spec/latest/json-ld-api/#rdf-conversion-algorithms
> specify that **when JSON-LD is interpreted as RDF,** (i.e., when the
> JSON-LD model is converted to the RDF model) skolem IRIs MUST be
> generated using the well-known URI suffix "json-ld-genid" for any
> JSON-LD blank node that would otherwise be mapped to an RDF blank node
> in a position where an RDF blank node is not permitted.  Conversely,
> when RDF is serialized as JSON-LD (or when an RDF model is converted to
> a JSON-LD model), skolem IRIs having the well-known URI suffix
> "json-ld-genid" SHOULD be serialized as JSON-LD blank nodes.  Finally,
> register the well-known URI suffix "json-ld-genid", in accordance with
> RFC5785:
> http://tools.ietf.org/html/rfc5785
> BACKGROUND NOTE: The existing well-known URI suffix "genid" is for
> converting to/from RDF blank nodes (in positions where blank nodes are
> *permitted* in RDF), whereas "json-ld-genid" will be used for *avoiding*
> blank nodes (in positions where they are not allowed in RDF).
> ]]
> There was also some follow up email discussion about what  well-known URI suffix to use, but that is probably a minor issue.
> Before making a decision about this proposal, the JSON-LD group would like to know whether others think this proposal is reasonable and viable.  The goal is to make JSON-LD function more predictably as a concrete RDF syntax.  At present, such skolemization is optional, which means that a user cannot be assured of obtaining legal RDF or knowing whether the otherwise-illegal triples will simply be dropped.
> Please let us know your thoughts.
> Thanks,
> David

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Received on Saturday, 15 June 2013 17:41:04 UTC

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