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

From: Gregg Kellogg <gregg@greggkellogg.com>
Date: Mon, 1 Jul 2013 09:21:11 -0600
Cc: "'David Booth'" <david@dbooth.org>, "'Pat Hayes'" <phayes@ihmc.us>, "'www-archive'" <www-archive@w3.org>, "'Andy Seaborne'" <andy@apache.org>, "'Manu Sporny'" <msporny@digitalbazaar.com>, "'Hawke, Sandro'" <sandro@w3.org>, "'Wood, David'" <david@3roundstones.com>, "'David Longley'" <dlongley@digitalbazaar.com>
Message-Id: <B828CB19-8E6A-4C44-AD95-68B0EB0FE206@greggkellogg.com>
To: Markus Lanthaler <markus.lanthaler@gmx.net>
On Jul 1, 2013, at 8:33 AM, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:

> On Monday, July 01, 2013 4:07 PM, David Booth wrote:
>> On 07/01/2013 05:41 AM, Markus Lanthaler wrote:
>>> You seem to suggest that we remove a mechanism that allows to map
>>> data to something close enough to RDF that some RDF systems already
>>> support.
>> 
>> Yes, I am suggesting that the feature of permitting blank nodes in that
>> JSON-LD position -- the position that would result in blank predicates
>> in the RDF model -- be removed.   Users would instead be required to
>> use URIs in those cases instead of blank nodes.
> 
> Or, more likely, they would just not map those properties at all and the
> data would be lost due to that.

It seems to me that this is not a JSON-LD issue, but an issue about Generalized RDF Triples. These are described in [RDF11-Concepts] [1]. Given the description of an Generalized RDF Triple/Graph/Dataset, is it required that there be some form of transformation from a generalized version to a RDF Triple? If so, then it affects BNode predicates, but also literal subject/predicate.

IMO, I think it's sufficient to say that we generate a generalized RDF Dataset and provide some advice on how a Generalized Dataset (at least the subset of these created by JSON-LD) can be turned into an RDF Dataset, ideally referencing something that is not JSON-LD specific.

Gregg

[1] https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#section-generalized-rdf

>>> IMO, that's also information loss.
>> 
>> I would consider it a feature loss rather than information loss, since a
>> user could still represent the information.  The user would just have to
>> use a URI instead of a blank node.   Is there an important use case for
>> permitting blank nodes in the JSON-LD position that would map them to
>> blank node predicates in RDF?  If so, what is it?
> 
> If you look at JSON, you could say that all properties are effectively
> bnodes because they have just local meaning. Sometimes you wanna preserve
> that data when transforming the JSON-LD using one of the transformation
> algorithms.
> 
> Another use case is, for instance, if just wanna extract nodes of a certain
> type. Let's say all persons that occur in a graph. In that case it is enough
> to map the properties you are interested in to IRIs and threat all the
> others as blank node predicates.
> 
> For example, you may have a JSON representation of a blog post and all its
> comments:
> 
> ...
> comments: [
>  {
>    text: ...
>    author: 
>      {
>        name: ...
>        .. other properties you are interested in ...
>      }
>  }
> ]
> 
> You could extract the all persons by mapping name to foaf:name etc. and all
> other properties to blank nodes:
> 
> {
>  "@context": {
>    "@vocab": "_:",
>    "name": "http://xmlns.com/foaf/0.1/name",
>    ...
>  }
> }
> 
> and then just filter out the nodes which have a foaf:name.
> 
> If you wouldn't map all other properties to blank nodes you wouldn't get any
> triples at all as we ignore unmapped properties (and their complete
> subtrees).
> 
> 
> 
> --
> Markus Lanthaler
> @markuslanthaler
> 
Received on Monday, 1 July 2013 15:21:42 UTC

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