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Re: Official response to RDF-ISSUE-132: JSON-LD/RDF Alignment -- Sub-issue on the relationship between JSON-LD and RDF

From: Sandro Hawke <sandro@w3.org>
Date: Tue, 11 Jun 2013 01:20:25 -0400
Message-ID: <51B6B399.7040200@w3.org>
To: David Booth <david@dbooth.org>
CC: public-rdf-comments@w3.org
On 06/11/2013 12:17 AM, David Booth wrote:
> Below is a specific proposal for resolving the issue that the 
> normative relationship between JSON-LD and RDF is not clear, and the 
> JSON-LD model is not fully aligned with the RDF model.  It clarifies 
> that JSON-LD is a concrete syntax for RDF and ensures complete 
> alignment with RDF while avoiding additional early mentions of RDF in 
> the document.
>
> For substantive changes:
>
> 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).
>

-0    This is too clever by half, I think.

If we're talking about blank nodes for predicates, well, people will 
just learn not to use them, I expect.  Or they'll start to use them in 
Turtle, too.   And maybe RDFa and RDF/XML using Skolem IDs, but then 
"json" will be a misnomer.     So for this hack, at least call it 
"generalized-rdf-genid" or something like that.

For blank node graph names, let's see how ISSUE-131 comes out.   But 
again, I don't see that JSON-LD is any different from any of the other 
syntaxes on this front -- people using them want these features, too.

> 2. Make any other changes needed to ensure that JSON-LD is a normative 
> concrete syntax for RDF.  (Are any other changes needed?)
>
> For editorial changes:
>
> 3. In section 1
> https://dvcs.w3.org/hg/json-ld/raw-file/default/spec/latest/json-ld/index.html#introduction 
>
> make the following editorial change to clarify and move the mention of 
> RDF slightly later in the document.  Delete the sentence: "Developers 
> that require any of the facilities listed above or need to serialize 
> an RDF graph or dataset [RDF11-CONCEPTS] in a JSON-based syntax will 
> find JSON-LD of interest.".  Instead, add the following bullet item to 
> the existing bullet list in section 1.1:
>
>  - "Software developers who want to generate or consume Linked
>    Data, an RDF graph or an RDF Dataset in a JSON syntax."
>
> 4. Without adding any earlier mention of RDF than the JSON-LD spec 
> already contains, make other editorial changes as needed to avoid 
> implying that JSON-LD is not necessarily RDF.  (However it is fine to 
> say that JSON-LD does not need to be *processed* as RDF.)  Some examples:
>
>  - Change "Converting JSON-LD to RDF" to either "Interpreting JSON-LD 
> as RDF" or "Converting a JSON-LD model to an RDF model".
>
>  - Change "Convert to RDF Algorithm" to "Interpret as RDF Algorithm" 
> or "Algorithm for Interpreting JSON-LD as RDF".
>
>  - Change "Convert from RDF Algorithm" to "Serialize from RDF 
> Algorithm" or "Algorithm for Serializing RDF as JSON-LD".
>
>  - Change "This algorithms converts a JSON-LD document to an RDF 
> dataset" to "This algorithm interprets a JSON-LD document as an RDF 
> dataset".
>
>  - Change "This algorithm converts an RDF dataset" to "This algorithm 
> serializes an RDF dataset".
>
>  - Change "turning a JSON-LD document" to "interpreting a JSON-LD 
> document as RDF".
>
> There are many other instances in the JSON-LD document, and I would be 
> happy to help find and fix them.  Most of them can be found by 
> searching for the verb "convert" and changing it to "interpret" or 
> "serialize". Alternatively you could say "deserialize" instead of 
> "interpret".
>
> 5. At the beginning of appendix C insert: "JSON-LD is a _concrete RDF 
> syntax_ as described in [RDF11_CONCEPTS].  Hence, a JSON-LD document 
> is both an RDF document and a JSON document and correspondingly 
> represents both an instance of the RDF data model and an instance of 
> the JSON-LD data model."
>

0 on all these.  They seem harmless but unnecessary to me.

> 6. In appendix C change the following paragraph in accordance with #1 
> above:
> [[
> Summarized these differences mean that JSON-LD is capable of 
> serializing any RDF graph or dataset and most, but not all, JSON-LD 
> documents can be directly transformed to RDF. It is possible to work 
> around this restriction, when converting JSON-LD to RDF, by converting 
> blank nodes used as graph names or properties to IRIs, minting new 
> "Skolem IRIs" as per Replacing Blank Nodes with IRIs of 
> [RDF11-CONCEPTS]. A complete description of the algorithms to convert 
> from RDF to JSON-LD and from JSON-LD to RDF is included in the JSON-LD 
> Processing Algorithms and API specification [JSON-LD-API].
> ]]
>
> to:
> [[
> The algorithm for interpreting JSON-LD as RDF is specified in the 
> JSON-LD Processing Algorithms and API specification [JSON-LD-API], 
> which is hereby normatively included by reference.
> ]]

That makes sense, but we didn't structure it that way because we feared 
problems with json-ld-api would prevend json-ld from going to REC.

-0.5

>
> 7. In section C.1
> https://dvcs.w3.org/hg/json-ld/raw-file/default/spec/latest/json-ld/index.html#transformation-from-json-ld-to-rdf 
>
> make the following changes:
>
> a. Change the title from "Transformation from JSON-LD to RDF" to 
> "Brief Overview of Interpreting JSON-LD as RDF".
>
> b. After "This section is non-normative." add: "The complete, 
> normative algorithm for interpreting JSON-LD as RDF is defined in the 
> JSON-LD Processing Algorithms and API specification [JSON-LD-API] 
> secion 10."
>

Falls out of decisions above.

     -- Sandro

> Thanks,
> David
>
>
>
>
>
>
>
Received on Tuesday, 11 June 2013 05:20:39 UTC

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