Module: JSON::LD::ToRDF

Includes:
Utils
Included in:
API, StreamingReader
Defined in:
lib/json/ld/to_rdf.rb

Instance Method Summary collapse

Methods included from Utils

#add_value, #as_array, #as_resource, #blank_node?, #compare_values, #graph?, #has_value?, #index?, #list?, #node?, #node_or_ref?, #node_reference?, #property?, #simple_graph?, #value?

Instance Method Details

#item_to_rdf(item, graph_name: nil, quoted: false) {|statement| ... } ⇒ Object

Returns RDF::Resource the subject of this item.

Parameters:

  • item (Hash{String => Object})
  • graph_name (RDF::Resource) (defaults to: nil)
  • quoted (Boolean) (defaults to: false) —

    emitted triples are quoted triples.

Yields:

  • statement

Yield Parameters:

Returns:

  • RDF::Resource the subject of this item



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# File 'lib/json/ld/to_rdf.rb', line 19

def item_to_rdf(item, graph_name: nil, quoted: false, &block)
  # Just return value object as Term
  return unless item

  if value?(item)
    value = item.fetch('@value')
    datatype = item.fetch('@type', nil)

    datatype = RDF_JSON if datatype == '@json'

    case value
    when RDF::Value
      return value
    when TrueClass, FalseClass
      # If value is true or false, then set value its canonical lexical form as defined in the section Data Round Tripping. If datatype is null, set it to xsd:boolean.
      value = value.to_s
      datatype ||= RDF::XSD.boolean.to_s
    when Numeric
      # Otherwise, if value is a number, then set value to its canonical lexical form as defined in the section Data Round Tripping. If datatype is null, set it to either xsd:integer or xsd:double, depending on if the value contains a fractional and/or an exponential component.
      value = if datatype == RDF_JSON
        value.to_json_c14n
      else
        # Don't serialize as double if there are no fractional bits
        as_double = value.ceil != value || value >= 1e21 || datatype == RDF::XSD.double
        lit = if as_double
          RDF::Literal::Double.new(value, canonicalize: true)
        else
          RDF::Literal.new(value.numerator, canonicalize: true)
        end

        datatype ||= lit.datatype
        lit.to_s.sub("E+", "E")
      end
    when Array, Hash
      # Only valid for rdf:JSON
      value = value.to_json_c14n
    else
      if item.key?('@direction') && @options[:rdfDirection]
        # Either serialize using a datatype, or a compound-literal
        case @options[:rdfDirection]
        when 'i18n-datatype'
          datatype = RDF::URI("https://www.w3.org/ns/i18n##{item.fetch('@language',
            '').downcase}_#{item['@direction']}")
        when 'compound-literal'
          cl = RDF::Node.new
          yield RDF::Statement(cl, RDF.value, item['@value'].to_s)
          yield RDF::Statement(cl, RDF_LANGUAGE, item['@language'].downcase) if item['@language']
          yield RDF::Statement(cl, RDF_DIRECTION, item['@direction'])
          return cl
        end
      end

      # Otherwise, if datatype is null, set it to xsd:string or xsd:langString, depending on if item has a @language key.
      datatype ||= item.key?('@language') ? RDF.langString : RDF::XSD.string
      value = value.to_json_c14n if datatype == RDF_JSON
    end
    datatype = RDF::URI(datatype) if datatype && !datatype.is_a?(RDF::URI)

    # Initialize literal as an RDF literal using value and datatype. If element has the key @language and datatype is xsd:string, then add the value associated with the @language key as the language of the object.
    language = item.fetch('@language', nil) if datatype == RDF.langString
    return RDF::Literal.new(value, datatype: datatype, language: language)
  elsif list?(item)
    # If item is a list object, initialize list_results as an empty array, and object to the result of the List Conversion algorithm, passing the value associated with the @list key from item and list_results.
    return parse_list(item['@list'], graph_name: graph_name, &block)
  end

  subject = case item['@id']
  when nil then node
  when String then as_resource(item['@id'])
  when Object
    # Embedded/quoted statement
    # (No error checking, as this is done in expansion)
    to_enum(:item_to_rdf, item['@id'], quoted: true).to_a.first
  end

  # log_debug("item_to_rdf")  {"subject: #{subject.to_ntriples rescue 'malformed rdf'}"}
  item.each do |property, values|
    case property
    when '@type'
      # If property is @type, construct triple as an RDF Triple composed of id, rdf:type, and object from values where id and object are represented either as IRIs or Blank Nodes
      values.each do |v|
        object = as_resource(v)
        # log_debug("item_to_rdf")  {"type: #{object.to_ntriples rescue 'malformed rdf'}"}
        yield RDF::Statement(subject, RDF.type, object, graph_name: graph_name, quoted: quoted)
      end
    when '@graph'
      values = [values].compact unless values.is_a?(Array)
      values.each do |nd|
        item_to_rdf(nd, graph_name: subject, quoted: quoted, &block)
      end
    when '@reverse'
      raise "Huh?" unless values.is_a?(Hash)

      values.each do |prop, vv|
        predicate = as_resource(prop)
        # log_debug("item_to_rdf")  {"@reverse predicate: #{predicate.to_ntriples rescue 'malformed rdf'}"}
        # For each item in values
        vv.each do |v|
          # Item is a node definition. Generate object as the result of the Object Converstion algorithm passing item.
          object = item_to_rdf(v, graph_name: graph_name, &block)
          # log_debug("item_to_rdf")  {"subject: #{object.to_ntriples rescue 'malformed rdf'}"}
          # yield subject, prediate, and literal to results.
          yield RDF::Statement(object, predicate, subject, graph_name: graph_name, quoted: quoted)
        end
      end
    when '@included'
      values.each do |v|
        item_to_rdf(v, graph_name: graph_name, &block)
      end
    when /^@/
      # Otherwise, if @type is any other keyword, skip to the next property-values pair
    else
      # Otherwise, property is an IRI or Blank Node identifier
      # Initialize predicate from  property as an IRI or Blank node
      predicate = as_resource(property)
      # log_debug("item_to_rdf")  {"predicate: #{predicate.to_ntriples rescue 'malformed rdf'}"}

      # For each item in values
      values.each do |v|
        if list?(v)
          # log_debug("item_to_rdf")  {"list: #{v.inspect}"}
          # If item is a list object, initialize list_results as an empty array, and object to the result of the List Conversion algorithm, passing the value associated with the @list key from item and list_results.
          object = parse_list(v['@list'], graph_name: graph_name, &block)

          # Append a triple composed of subject, prediate, and object to results and add all triples from list_results to results.
        else
          # Otherwise, item is a value object or a node definition. Generate object as the result of the Object Converstion algorithm passing item.
          object = item_to_rdf(v, graph_name: graph_name, &block)
          # log_debug("item_to_rdf")  {"object: #{object.to_ntriples rescue 'malformed rdf'}"}
          # yield subject, prediate, and literal to results.
        end
        yield RDF::Statement(subject, predicate, object, graph_name: graph_name, quoted: quoted)
      end
    end
  end

  subject
end

#node ⇒ Object

Create a new named node using the sequence



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# File 'lib/json/ld/to_rdf.rb', line 191

def node
  RDF::Node.new(namer.get_sym)
end

#parse_list(list, graph_name: nil) {|statement| ... } ⇒ Array<RDF::Statement>

Parse a List

Parameters:

  • list (Array) —

    The Array to serialize as a list

Yields:

  • statement

Yield Parameters:

  • statement (RDF::Resource)

Returns:



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# File 'lib/json/ld/to_rdf.rb', line 167

def parse_list(list, graph_name: nil, &block)
  # log_debug('parse_list') {"list: #{list.inspect}"}

  last = list.pop
  result = first_bnode = last ? node : RDF.nil

  list.each do |list_item|
    # Set first to the result of the Object Converstion algorithm passing item.
    object = item_to_rdf(list_item, graph_name: graph_name, &block)
    yield RDF::Statement(first_bnode, RDF.first, object, graph_name: graph_name)
    rest_bnode = node
    yield RDF::Statement(first_bnode, RDF.rest, rest_bnode, graph_name: graph_name)
    first_bnode = rest_bnode
  end
  if last
    object = item_to_rdf(last, graph_name: graph_name, &block)
    yield RDF::Statement(first_bnode, RDF.first, object, graph_name: graph_name)
    yield RDF::Statement(first_bnode, RDF.rest, RDF.nil, graph_name: graph_name)
  end
  result
end