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

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?

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
>
>
>