Serializations

The RDF.ex package comes with implementations of the N-Triples, N-Quads and Turtle serialization formats. Formats which require additional dependencies should be implemented in separate Hex packages. The JSON-LD format for example is available with the JSON-LD.ex package.

RDF graphs and datasets can be read and written to files or strings in a RDF serialization format using the read_file, read_string and write_file, write_string functions of the resp. RDF.Serialization.Format module.

{:ok, graph} = RDF.NTriples.read_file("/path/to/some_file.nt")
{:ok, nquad_string} = RDF.NQuads.write_string(graph)

All of the read and write functions are also available in bang variants which will fail in error cases.

All of these read_* and write_* functions are also available in the top-level RDF module, where the serialization format can be specified in various ways, either by providing the format name via the format option, or via the media_type option.

{:ok, graph} = RDF.read_file("/path/to/some_file", format: :turtle)
json_ld_string = RDF.write_string!(graph, media_type: "application/ld+json")

Note: The later command requires the json_ld package to be defined as a dependency in the Mixfile of your application.

The file read and write functions are also able to infer the format from the file extension of the given filename.

RDF.read_file!("/path/to/some_file.ttl")
|> RDF.write_file!("/path/to/some_file.jsonld")

Base IRI

For serialization formats which support it, you can provide a base IRI on the read functions with the base option. You can also provide a default base IRI in your application configuration, which will be used when no base option is given.

config :rdf,
  default_base_iri: "http://my_app.example/"

Managing prefixes

The prefixes used in serialization formats which support this can be managed in various ways.

An RDF.Graph contains a mapping of prefixes to IRI namespaces. You can add prefixes with RDF.Graph.add_prefixes/2. The mapping can given as a map or keyword lists, where the prefixes might be given as atoms or strings, while the IRI namespaces can be given as RDF.IRIs, strings or as RDF.Vocabulary.Namespace modules. You can use any combinations of these different types, prefixes are stored internally always as atoms and IRI namespaces always as RDF.IRIs.

graph
|> RDF.Graph.add_prefixes(ex: EX, schema: ~I<http://schema.org/>)
|> RDF.Graph.add_prefixes(%{"ex2" => "http://example2.com/"})

A single prefix or a list of multiple prefixes can be deleted with RDF.Graph.delete_prefixes/2.

graph
|> RDF.Graph.delete_prefixes("ex"])
|> RDF.Graph.delete_prefixes([:ex2, :schema])

When a graph is read from such serialization format the deserialized prefixes are automatically stored in the RDF.Graph structure.

Writing a RDF data structure gives you more options for which prefixes should be serialized:

  1. The prefixes option of the write_* functions can be used provide prefix mappings in all the different ways mentionend above and always have the highest precedence.
  2. If the RDF data to be serialized is given as a RDF.Graph with defined prefixes these are used, when no prefixes are given with prefixes option otherwise.
  3. As a fallback when prefixes are not defined in these ways the RDF.default_prefixes/0 are used. You can configure these with the default_prefixes compile-time configuration in your confix.exs files:
config :rdf,
  default_prefixes: %{
    ex: "http://example.com/"
  }
  1. The RDF.default_prefixes/0 always contain the RDF.standard_prefixes/0 consisting of prefixes the usual xsd, rdf and rdfs prefixes. If you don't want to use these RDF.standard_prefixes/0 for your default_prefixes you'll explicitly have to disable them with the use_standard_prefixes compile-time configuration option.
config :rdf,
  use_standard_prefixes: false