Re: Type of external @context param when serializing RDF::Graph to JSON-LD

On Aug 17, 2013, at 1:07 PM, Jindřich Mynarz <mynarzjindrich@gmail.com> wrote:

> Hi Gregg,
> 
> thanks for a quick and in-depth reply. Now it's much clearer to me how to provide external JSON-LD @context.
> 
> Could you please also clarify the example in https://github.com/ruby-rdf/json-ld/blob/master/README.md that uses JSON::LD::API.fromRDF(input, context) even though you made it clear that the fromRDF method doesn't accept context as the second param?

Sure, thanks for noticing that. The README needs a little attention.

Gregg

> Best,
> 
> Jindrich
> 
> -- 
> Jindrich Mynarz
> http://mynarz.net/#jindrich
> 
> 
> On Sat, Aug 17, 2013 at 8:14 PM, Gregg Kellogg <gregg@greggkellogg.com> wrote:
> On Aug 17, 2013, at 3:55 AM, Jindřich Mynarz <mynarzjindrich@gmail.com> wrote:
> 
>> Hi,
>> 
>> I want to use ruby-rdf/json-ld to serialize RDF::Graph into JSON-LD given an external @context. The examples at https://github.com/ruby-rdf/json-ld/ suggest using JSON::LD::API::fromRDF(input, context). I noticed that the input param should be an instance of RDF::Graph, however, it's not clear to me what type should the context param be. Documentation for JSON::LD::API::fromRDF states that the second parameter is [Hash{Symbol => Object}] options, not @context. How should I provide an external @context when serializing RDF::Graph to JSON-LD? As a file path, String, Hash or as an instance of JSON::LD:Context? How could you do the same when using RDF::Graph#dump directly?
> 
> The JSON::LD gem closely follows the JSON-LD API specification, but is more of a ruby-like gem then a JavaScript/Promise API as it is synchronous. You can view the online documentation here: http://rubydoc.info/github/ruby-rdf/json-ld/master/frames.
> 
> You can either using the fromRDF API method, or the standard RDF.rb readers and writers, which allows the use of dump() method.
> 
> The fromRDF class method [1] does not take a context, as it outputs expanded JSON-LD. If you wanted to compact it using a context, you could add a compact call [2], such as the following:
> 
>     JSON::LD::API.fromRDF(graph) do |expanded|
>       JSON::LD::API.compact(expanded, context) do |compacted|
>         puts compacted.to_json
>       end
>     end
> 
> From the compact documentation, you can see that the context parameter accepts a String, something responding to #read, Hash, Array or JSON::LD::Context. In the case of a string, it is interpreted as a file path or URL from which to load a context.
> 
> From the JSON::LD::Writer.initialize documentation [3], you can see that there is a :context option, which is treated just like the context parameter to compact. Because this is a general Writer interface, as used elsewhere in RDF.rb, this means that it could be added to a dump() call, such as the following
> 
>     g = RDF::Graph.load("file.ttl")
>     puts g.dump(:jsonld, :context => context)
> 
> If you use prefix and base definitions instead, it will create a new context and use that for compacting the output; this is common when transcoding between different RDF formats.
> 
> Gregg
> 
> [1] http://rubydoc.info/github/ruby-rdf/json-ld/master/JSON/LD/API#fromRDF-class_method
> [2] http://rubydoc.info/github/ruby-rdf/json-ld/master/JSON/LD/API#compact-class_method
> [3] http://rubydoc.info/github/ruby-rdf/json-ld/master/JSON/LD/Writer#initialize-instance_method
> 
> 
>> Best,
>> 
>> Jindrich
>> 
>> -- 
>> Jindrich Mynarz
>> http://mynarz.net/#jindrich
> 
>