W3C home > Mailing lists > Public > public-linked-json@w3.org > July 2013

Re: Convert also "partial" lists from RDF to JSON-LD

From: Gregg Kellogg <gregg@greggkellogg.net>
Date: Fri, 5 Jul 2013 10:49:58 -0600
Cc: <public-rdf-wg@w3.org>, <public-linked-json@w3.org>, "'Andy Seaborne'" <andy@apache.org>
Message-Id: <093FE9C2-216B-4FB9-A8AF-EC299255435E@greggkellogg.net>
To: Markus Lanthaler <markus.lanthaler@gmx.net>

Gregg Kellogg
gregg@greggkellogg.net

On Jul 5, 2013, at 4:02 AM, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:

> CC'ing public-linked-json as this discussion might result in a change to the
> algorithms and may help the OpenAnnotation people.
> 
> 
> On Thursday, July 04, 2013 10:21 PM, Andy Seaborne wrote:
>> The set of all heads of well-formed lists can be found quite easily.
>> 
>> All lists have a common tail (rdf:nil).  Just walk back up the list
>> checking nodes have exactly one rdf:first and one rdf:next triple.
>> This generates the list head.
> 
> You are of course right and the necessary changes to the algorithm should be
> quite small.
> 
> Currently a @list can never be the value of a rdf:first/rdf:rest. This kind
> of ensures that only "complete" lists are transformed to @list and that we
> don't produce lists of lists in JSON-LD.
> 
> An example might clarify what I mean. Currently we would never produce
> something like
> 
>  {
>    "@id": "http://example.com/",
>    "rdf:first": "A",
>    "rdf:rest": { "@list": [ "B", "C", "D" ] }
>  }
> 
> all the list bnodes would be preserved:
> 
>  [
>    {
>      "@id": "http://example.com/",
>      "rdf:first": "A",
>      "rdf:rest": { "@list": [ "B", "C", "D" ] }
>    },
>    {
>       "@id": "_:b0",
>       "rdf:first": "B"
>       "rdf:rest": { "@id": "_:b1" }
>    },
>    ...
>  ]
> 
> 
> Arguably changing that would result in a nicer result. This might also be a
> quite elegant solution for the OpenAnnotation people. I think we could
> threat this change as an algorithmic bug fix (meaning, no need for another
> LC).
> 
> I've created ISSUE-277 for this:
>  https://github.com/json-ld/json-ld.org/issues/277
> 
> 
> Thoughts?

(From my comment on the issue:)

The @id of the first object can't be "http://example.com/", surely? To be a list, the subject must be a BNode.

It also makes sense that @list can be the value of rdf:rest (and perhaps rdf:first, as well). The algorithm would find the list head at the first node having rdf:first/rest with only single well-formed values, as it does now; this should include those for which the subject is a non-well-formed value of an rdf:rest.

An example @afs and I were working on offline is more like the following:

Turtle:

@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix : <http://example/> .

:x :list _:a .

_:a rdf:first 1 .
_:a :additional "foo" .
_:a rdf:rest  _:b .

_:b rdf:first 2 .
_:b rdf:rest  _:c .

_:c rdf:first 3 .
_:c rdf:rest  rdf:nil .

JSON-LD:

{
  "@context": {...},
  "@id": "_:x",
  "list": {
    "additional": "foo",
    "rdf:first": 1,
    "rdf:rest: {"@list": [2, 3]}
  }
}

Gregg

> --
> Markus Lanthaler
> @markuslanthaler
> 
> 
Received on Friday, 5 July 2013 16:50:34 UTC

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