Module: JSON::LD::FromRDF

Includes:
Utils
Included in:
API
Defined in:
lib/json/ld/from_rdf.rb

Instance Method Summary collapse

Methods included from Utils

#as_resource, #blank_node?, #index?, #list?, #node?, #node_reference?, #value?

Instance Method Details

#from_statements(input) ⇒ Array<Hash>

Generate a JSON-LD array representation from an array of ‘RDF::Statement`. Representation is in expanded form

Parameters:

  • input (Array<RDF::Statement>, RDF::Enumerable)

Returns:

  • (Array<Hash>) —

    the JSON-LD document in normalized form



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# File 'lib/json/ld/from_rdf.rb', line 13

def from_statements(input)
  default_graph = {}
  graph_map = {'@default' => default_graph}

  value = nil
  ec = Context.new

  # Create a map for node to object representation

  # For each triple in input
  input.each do |statement|
    debug("statement") { statement.to_nquads.chomp}

    name = statement.context ? ec.expand_iri(statement.context).to_s : '@default'
    
    # Create a graph entry as needed
    node_map = graph_map[name] ||= {}
    default_graph[name] ||= {'@id' => name} unless name == '@default'
    
    subject = ec.expand_iri(statement.subject).to_s
    node = node_map[subject] ||= {'@id' => subject}

    # If object is an IRI or blank node identifier, does not equal rdf:nil, and node map does not have an object member, create one and initialize its value to a new JSON object consisting of a single member @id whose value is set to object.
    node_map[statement.object.to_s] ||= {'@id' => statement.object.to_s} unless
    statement.object.literal? || statement.object == RDF.nil

    # If predicate equals rdf:type, and object is an IRI or blank node identifier, append object to the value of the @type member of node. If no such member exists, create one and initialize it to an array whose only item is object. Finally, continue to the next RDF triple.
    if statement.predicate == RDF.type && statement.object.resource?
      merge_value(node, '@type', statement.object.to_s)
      next
    end

    # If object equals rdf:nil and predicate does not equal rdf:rest, set value to a new JSON object consisting of a single member @list whose value is set to an empty array.
    value = if statement.object == RDF.nil && statement.predicate != RDF.rest
      {'@list' => []}
    else
      ec.expand_value(nil, statement.object, @options)
    end

    merge_value(node, statement.predicate.to_s, value)

    # If object is a blank node identifier and predicate equals neither rdf:first nor rdf:rest, it might represent the head of a RDF list:
    if statement.object.node? && ![RDF.first, RDF.rest].include?(statement.predicate)
      merge_value(node_map[statement.object.to_s], :usages, value)
    end
  end

  # For each name and graph object in graph map:
  graph_map.each do |name, graph_object|
    subjects = graph_object.keys
    subjects.each do |subj|
      next unless graph_object.has_key?(subj)
      node = graph_object[subj]
      next unless node[:usages].is_a?(Array) && node[:usages].length == 1
      debug("list head") {node.to_json(JSON_STATE)}
      value = node[:usages].first
      list, list_nodes, subject = [], [], subj

      while subject != RDF.nil.to_s && list
        if node.nil? ||
           !blank_node?(node) ||
           node.keys.any? {|k| !["@id", :usages, RDF.first.to_s, RDF.rest.to_s].include?(k)} ||
           !(f = node[RDF.first.to_s]).is_a?(Array) || f.length != 1 ||
           !(r = node[RDF.rest.to_s]).is_a?(Array) || r.length != 1 || !node_reference?(r.first) ||
           list_nodes.include?(subject)

          debug("list") {"not valid list element: #{node.to_json(JSON_STATE)}"}
          list = nil
        else
          list << f.first
          list_nodes << node['@id']
          subject = r.first['@id']
          node = graph_object[subject]
          debug("list") {"rest: #{node.to_json(JSON_STATE)}"}
          list = nil if list_nodes.include?(subject)
        end
      end

      next if list.nil?
      value.delete('@id')
      value['@list'] = list
      list_nodes.each {|s| graph_object.delete(s)}
    end
  end

  result = []
  debug("graph_map") {graph_map.to_json(JSON_STATE)}
  default_graph.keys.sort.each do |subject|
    node = default_graph[subject]
    if graph_map.has_key?(subject)
      node['@graph'] = []
      graph_map[subject].keys.sort.each do |s|
        n = graph_map[subject][s]
        n.delete(:usages)
        node['@graph'] << n
      end
    end
    node.delete(:usages)
    result << node
  end
  debug("fromRDF") {result.to_json(JSON_STATE)}
  result
end