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

#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

#from_statements(dataset, useRdfType: false, useNativeTypes: false, extendedRepresentation: false) ⇒ Array<Hash>

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

Parameters:

  • dataset (Array<RDF::Statement>, RDF::Enumerable)
  • useRdfType (Boolean) (defaults to: false) —

    (false) If set to true, the JSON-LD processor will treat rdf:type like a normal property instead of using @type.

  • useNativeTypes (Boolean) (defaults to: false) —

    (false) use native representations

  • extendedRepresentation (false) (defaults to: false) —

    Use the extended internal representation for native types.

Returns:

  • (Array<Hash>) —

    the JSON-LD document in normalized form



22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
 
# File 'lib/json/ld/from_rdf.rb', line 22

def from_statements(dataset, useRdfType: false, useNativeTypes: false, extendedRepresentation: false)
  default_graph = {}
  graph_map = { '@default' => default_graph }
  referenced_once = {}

  value = nil

  # Create an entry for compound-literal node detection
  compound_literal_subjects = {}

  # Create a map for node to object representation

  # For each statement in dataset
  dataset.each do |statement|
    # log_debug("statement") { statement.to_nquads.chomp}

    name = if statement.graph_name
      @context.expand_iri(statement.graph_name,
        base: @options[:base]).to_s
    else
      '@default'
    end

    # Create a graph entry as needed
    node_map = graph_map[name] ||= {}
    compound_literal_subjects[name] ||= {}

    default_graph[name] ||= { '@id' => name } unless name == '@default'

    subject = if statement.subject.statement?
      resource_representation(statement.subject, useNativeTypes, extendedRepresentation)['@id'].to_json_c14n
    else
      statement.subject.to_s
    end
    node = node_map[subject] ||= resource_representation(statement.subject, useNativeTypes,
      extendedRepresentation)

    # If predicate is rdf:datatype, note subject in compound literal subjects map
    if @options[:rdfDirection] == 'compound-literal' && statement.predicate == RDF_DIRECTION
      compound_literal_subjects[name][subject] ||= true
    end

    # If object is an IRI, blank node identifier, or statement, 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.
    unless statement.object.literal?
      object = if statement.object.statement?
        resource_representation(statement.object, useNativeTypes, extendedRepresentation)['@id'].to_json_c14n
      else
        statement.object.to_s
      end
      node_map[object] ||=
        resource_representation(statement.object, useNativeTypes, extendedRepresentation)
    end

    # 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? && !useRdfType
      merge_value(node, '@type', statement.object.to_s)
      next
    end

    # Set value to the result of using the RDF to Object Conversion algorithm, passing object, rdfDirection, and use native types.
    value = resource_representation(statement.object, useNativeTypes, extendedRepresentation)

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

    # If object is a blank node identifier or rdf:nil, it might represent the a list node:
    if statement.object == RDF.nil
      # Append a new JSON object consisting of three members, node, property, and value to the usages array. The node member is set to a reference to node, property to predicate, and value to a reference to value.
      object = node_map[statement.object.to_s]
      merge_value(object, :usages, {
        node: node,
        property: statement.predicate.to_s,
        value: value
      })
    elsif referenced_once.key?(statement.object.to_s)
      referenced_once[statement.object.to_s] = false
    elsif statement.object.node?
      referenced_once[statement.object.to_s] = {
        node: node,
        property: statement.predicate.to_s,
        value: value
      }
    end
  end

  # For each name and graph object in graph map:
  graph_map.each do |name, graph_object|
    # If rdfDirection is compound-literal, check referenced_once for entries from compound_literal_subjects
    compound_literal_subjects.fetch(name, {}).each_key do |cl|
      node = referenced_once[cl][:node]
      next unless node.is_a?(Hash)

      property = referenced_once[cl][:property]
      value = referenced_once[cl][:value]
      cl_node = graph_map[name].delete(cl)
      next unless cl_node.is_a?(Hash)

      node[property].select do |v|
        next unless v['@id'] == cl

        v.delete('@id')
        v['@value'] = cl_node[RDF.value.to_s].first['@value']
        if (langs = cl_node[RDF_LANGUAGE.to_s])
          lang = langs.first['@value']
          unless /^[a-zA-Z]{1,8}(-[a-zA-Z0-9]{1,8})*$/.match?(lang)
            warn "i18n datatype language must be valid BCP47: #{lang.inspect}"
          end
          v['@language'] = lang
        end
        v['@direction'] = cl_node[RDF_DIRECTION.to_s].first['@value']
      end
    end

    nil_var = graph_object.fetch(RDF.nil.to_s, {})

    # For each item usage in the usages member of nil, perform the following steps:
    nil_var.fetch(:usages, []).each do |usage|
      node = usage[:node]
      property = usage[:property]
      head = usage[:value]
      list = []
      list_nodes = []

      # If property equals rdf:rest, the value associated to the usages member of node has exactly 1 entry, node has a rdf:first and rdf:rest property, both of which have as value an array consisting of a single element, and node has no other members apart from an optional @type member whose value is an array with a single item equal to rdf:List, node represents a well-formed list node. Continue with the following steps:
      # log_debug("list element?") {node.to_json(JSON_STATE) rescue 'malformed json'}
      while property == RDF.rest.to_s &&
            blank_node?(node) &&
            referenced_once[node['@id']] &&
            node.keys.none? { |k| !["@id", '@type', :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 &&
            ((t = node['@type']).nil? || t == [RDF.List.to_s])
        list << Array(node[RDF.first.to_s]).first
        list_nodes << node['@id']

        # get next node, moving backwards through list
        node_usage = referenced_once[node['@id']]
        node = node_usage[:node]
        property = node_usage[:property]
        head = node_usage[:value]
      end

      head.delete('@id')
      head['@list'] = list.reverse
      list_nodes.each { |node_id| graph_object.delete(node_id) }
    end

    # Create annotations on graph object
    create_annotations(graph_object)
  end

  result = []
  default_graph.keys.opt_sort(ordered: @options[:ordered]).each do |subject|
    node = default_graph[subject]
    if graph_map.key?(subject)
      node['@graph'] = []
      graph_map[subject].keys.opt_sort(ordered: @options[:ordered]).each do |s|
        n = graph_map[subject][s]
        n.delete(:usages)
        node['@graph'] << n unless node_reference?(n)
      end
    end
    node.delete(:usages)
    result << node unless node_reference?(node)
  end
  # log_debug("fromRdf") {result.to_json(JSON_STATE) rescue 'malformed json'}
  result
end