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Re: JSON-LD Data model / RDF Data Model differences

From: Gavin Carothers <gavin@carothers.name>
Date: Tue, 30 Oct 2012 11:16:06 -0700
Message-ID: <CAPqY83zgze0RQzB0ob65GTXXqyzy+hHhT-CbjgFk_xJWyGHZDg@mail.gmail.com>
To: Manu Sporny <msporny@digitalbazaar.com>
Cc: RDF WG <public-rdf-wg@w3.org>
On Tue, Oct 30, 2012 at 11:03 AM, Manu Sporny <msporny@digitalbazaar.com> wrote:
> We had a small side-discussion at the F2F meeting today about
> differences between lists in the JSON-LD data model and lists in the RDF
> data model. This devolved/evolved into a re-hash of the JSON-LD data
> model vs. the RDF data model discussion:
>
> http://www.w3.org/2011/rdf-wg/wiki/JSON-LD_Data_Model
>
> I was going to start by ranting about RDF lists, but it seems I already
> did that back in May:
>
> "I really hate RDF Lists"
> http://lists.w3.org/Archives/Public/public-rdf-wg/2012May/0098.html
>
> Not having Graph/Dataset Literal as a primitive in RDF is also harming
> the RDF data model. We should be able to place a graph/dataset literal
> in the object position of an RDF triple. I don't expect that this group
> will be able to resolve either issue, but I just thought I'd throw this
> out there so that some of you might understand what is lacking in the
> RDF data model.
>
> Resolving these two issues above would help align the JSON-LD data model
> with the RDF data model, specifically:
>
> 1. "Graph names can be blank nodes." The question of whether or not
>    graph names can be blank nodes would have to be answered. I'd argue
>    that you should be able to name graphs using blank nodes.

We did resolve this. Graph labels must be IRIs.

> 2. "Lists are part of the data model." Lists are part of the data model
>    would be true for both models.
> 3. "Graphs/datasets are 'allowed' in the object position." Graphs would
>    be "allowed" in the object position in both models.

We did resolve this, we are not specifying graph literals nor dataset
literals at this time.

>
> We have simple answers to some of the other differences that would align
> the two data models.
>
> 1. "Unconnected nodes (IRIs, blank nodes or values) are supported." We
>    should add: "Authors SHOULD NOT use unconnected nodes (a node
>    definition that does not contain any properties) in JSON-LD
>    documents."
> 2. "Edge labels may be blank nodes." We should add: "Authors SHOULD
>    NOT use blank nodes as edge labels."
> 3. "Language tags are not normalized to lower case." We should add:
>    "JSON-LD processors MUST normalize all language tags to lowercase
>    when processing documents via the JSON-LD Algorithms."
> 4. "Scope of blank node labels". We should add: "Blank node labels are
>    scoped to the JSON-LD document."
>
> Which leaves these two differences between the JSON-LD data model and
> the RDF data model:
>
> 1. "Supports 'plain' strings, numbers and booleans, separately from
>    typed literals." This is true for TURTLE as well, so if there is a
>    problem with JSON-LD, then there is a problem with TURTLE when it
>    comes to this issue.
> 2. "Language maps are part of the data model." This is syntactic sugar
>    that was a requested "deal breaker" feature by the Drupal community.
>    If we don't include it, Drupal will willfully violate the JSON-LD
>    spec (or come up with their own solution). Digital Bazaar's
>    implementations will support Drupal by adding the feature to the
>    implementation, thus willfully violating the JSON-LD spec. The
>    difference in the data model does not result in any loss of
>    information when converting to RDF, other than the ability to
>    re-create the exact JSON-LD language-map structure when converting
>    back to JSON-LD from RDF. I personally don't think people will
>    care about not being able to round-trip language-maps from
>    JSON-LD to RDF and back to JSON-LD, but if they do, Gregg Kellogg
>    has proposed a mechanism that allows that to happen.
>
> Hope that is a helpful rundown of the differences between the two data
> models and my personal opinion of where we should be headed wrt. data
> model alignment.
>
> -- manu
>
> --
> Manu Sporny (skype: msporny, twitter: manusporny)
> President/CEO - Digital Bazaar, Inc.
> blog: HTML5 and RDFa 1.1
> http://manu.sporny.org/2012/html5-and-rdfa/
>
Received on Tuesday, 30 October 2012 18:16:38 GMT

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