Class: RDF::N3::Writer

Inherits:
Writer
  • Object
show all
Includes:
Util::Logger
Defined in:
vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb

Overview

A Turtle serialiser in Ruby

Note that the natural interface is to write a whole graph at a time. Writing statements or Triples will create a graph to add them to and then serialize the graph.

The writer will add prefix definitions, and use them for creating @prefix definitions, and minting QNames

Examples:

Obtaining a Turtle writer class

RDF::Writer.for(:n3)         #=> RDF::N3::Writer
RDF::Writer.for("etc/test.n3")
RDF::Writer.for("etc/test.ttl")
RDF::Writer.for(file_name:      "etc/test.n3")
RDF::Writer.for(file_name:      "etc/test.ttl")
RDF::Writer.for(file_extension: "n3")
RDF::Writer.for(file_extension: "ttl")
RDF::Writer.for(content_type:   "text/n3")

Serializing RDF graph into an Turtle file

RDF::N3::Writer.open("etc/test.n3") do |writer|
  writer << graph
end

Serializing RDF statements into an Turtle file

RDF::N3::Writer.open("etc/test.n3") do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Serializing RDF statements into an Turtle string

RDF::N3::Writer.buffer do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Creating @base and @prefix definitions in output

RDF::N3::Writer.buffer(base_uri: "http://example.com/", prefixes: {
    nil => "http://example.com/ns#",
    foaf: "http://xmlns.com/foaf/0.1/"}
) do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Author:

Constant Summary collapse

QNAME =
Meta::REGEXPS[:"http://www.w3.org/2000/10/swap/grammar/n3#qname"]

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(output = $stdout, options = {}) {|writer| ... } ⇒ Writer

Initializes the Turtle writer instance.

Parameters:

  • output (IO, File) (defaults to: $stdout)

    the output stream

  • options (Hash{Symbol => Object}) (defaults to: {})

    any additional options

Options Hash (options):

  • :encoding (Encoding) — default: Encoding::UTF_8

    the encoding to use on the output stream (Ruby 1.9+)

  • :canonicalize (Boolean) — default: false

    whether to canonicalize literals when serializing

  • :prefixes (Hash) — default: Hash.new

    the prefix mappings to use (not supported by all writers)

  • :base_uri (#to_s) — default: nil

    the base URI to use when constructing relative URIs

  • :max_depth (Integer) — default: 3

    Maximum depth for recursively defining resources, defaults to 3

  • :standard_prefixes (Boolean) — default: false

    Add standard prefixes to @prefixes, if necessary.

  • :default_namespace (String) — default: nil

    URI to use as default namespace, same as prefixes[nil]

  • :unique_bnodes (Boolean) — default: false

    Use unique node identifiers, defaults to using the identifier which the node was originall initialized with (if any).

Yields:

  • (writer)

    self

  • (writer)

Yield Parameters:

  • writer (RDF::Writer)
  • writer (RDF::Writer)

Yield Returns:

  • (void)


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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 108

def initialize(output = $stdout, options = {}, &block)
  super do
    @graph = RDF::Graph.new
    @uri_to_qname = {}
    @uri_to_prefix = {}
    if block_given?
      case block.arity
        when 0 then instance_eval(&block)
        else block.call(self)
      end
    end
  end
end

Instance Attribute Details

#base_uriURI

Returns Base URI used for relativizing URIs

Returns:

  • (URI)

    Base URI used for relativizing URIs



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 60

def base_uri
  @base_uri
end

#graphGraph

Returns Graph of statements serialized

Returns:

  • (Graph)

    Graph of statements serialized



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 58

def graph
  @graph
end

Class Method Details

.optionsObject

N3 Writer options



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 65

def self.options
  super + [
    RDF::CLI::Option.new(
      symbol: :max_depth,
      datatype: Integer,
      on: ["--max-depth"],
      description: "Maximum depth for recursively defining resources, defaults to 3.") {|arg| arg.to_i},
    RDF::CLI::Option.new(
      symbol: :default_namespace,
      datatype: RDF::URI,
      on: ["--default-namespace URI", :REQUIRED],
      description: "URI to use as default namespace, same as prefixes.") {|arg| RDF::URI(arg)},
  ]
end

Instance Method Details

#format_literal(literal, options = {}) ⇒ String

Returns the N-Triples representation of a literal.

Parameters:

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 231

def format_literal(literal, options = {})
  literal = literal.dup.canonicalize! if @options[:canonicalize]
  case literal
  when RDF::Literal
    case literal.datatype
    when RDF::XSD.boolean, RDF::XSD.integer, RDF::XSD.decimal
      literal.to_s
    when RDF::XSD.double
      literal.to_s.sub('E', 'e')  # Favor lower case exponent
    else
      text = quoted(literal.value)
      text << "@#{literal.language}" if literal.has_language?
      text << "^^#{format_uri(literal.datatype)}" if literal.has_datatype?
      text
    end
  else
    quoted(literal.to_s)
  end
end

#format_node(node, options = {}) ⇒ String

Returns the Turtle/N3 representation of a blank node.

Parameters:

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 269

def format_node(node, options = {})
  options[:unique_bnodes] ? node.to_unique_base : node.to_base
end

#format_uri(uri, options = {}) ⇒ String

Returns the Turtle/N3 representation of a URI reference.

Parameters:

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 257

def format_uri(uri, options = {})
  md = relativize(uri)
  log_debug {"relativize(#{uri.inspect}) => #{md.inspect}"} if md != uri.to_s
  md != uri.to_s ? "<#{md}>" : (get_qname(uri) || "<#{uri}>")
end

#get_qname(resource) ⇒ String?

Return a QName for the URI, or nil. Adds namespace of QName to defined prefixes

Parameters:

  • resource (RDF::Resource)

Returns:

  • (String, nil)

    value to use to identify URI



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 162

def get_qname(resource)
  case resource
  when RDF::Node
    return options[:unique_bnodes] ? resource.to_unique_base : resource.to_base
  when RDF::URI
    uri = resource.to_s
  else
    return nil
  end

  log_debug {"get_qname(#{resource}), std?}"}
  qname = case
  when @uri_to_qname.has_key?(uri)
    return @uri_to_qname[uri]
  when u = @uri_to_prefix.keys.detect {|u| uri.index(u.to_s) == 0}
    # Use a defined prefix
    prefix = @uri_to_prefix[u]
    prefix(prefix, u) unless u.to_s.empty? # Define for output
    log_debug {"get_qname: add prefix #{prefix.inspect} => #{u}"}
    uri.sub(u.to_s, "#{prefix}:")
  when @options[:standard_prefixes] && vocab = RDF::Vocabulary.each.to_a.detect {|v| uri.index(v.to_uri.to_s) == 0}
    prefix = vocab.__name__.to_s.split('::').last.downcase
    @uri_to_prefix[vocab.to_uri.to_s] = prefix
    prefix(prefix, vocab.to_uri) # Define for output
    log_debug {"get_qname: add standard prefix #{prefix.inspect} => #{vocab.to_uri}"}
    uri.sub(vocab.to_uri.to_s, "#{prefix}:")
  else
    nil
  end
  
  # Make sure qname is a valid qname
  if qname
    md = QNAME.match(qname)
    qname = nil unless md.to_s.length == qname.length
  end

  @uri_to_qname[uri] = qname
rescue Addressable::URI::InvalidURIError => e
  raise RDF::WriterError, "Invalid URI #{resource.inspect}: #{e.message}"
end

#indent(modifier = 0) ⇒ String (protected)

Returns indent string multiplied by the depth

Parameters:

  • modifier (Integer) (defaults to: 0)

    Increase depth by specified amount

Returns:

  • (String)

    A number of spaces, depending on current depth



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 398

def indent(modifier = 0)
  " " * (@depth + modifier)
end

#order_subjectsArray<Resource> (protected)

Order subjects for output. Override this to output subjects in another order.

Uses #top_classes and #base_uri.

Returns:

  • (Array<Resource>)

    Ordered list of subjects



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 305

def order_subjects
  seen = {}
  subjects = []
  
  # Start with base_uri
  if base_uri && @subjects.keys.include?(base_uri)
    subjects << base_uri
    seen[base_uri] = true
  end
  log_debug {"subjects1: #{subjects.inspect}"}
  
  # Add distinguished classes
  top_classes.each do |class_uri|
    graph.query(predicate:  RDF.type, object:  class_uri).
      map {|st| st.subject}.
      sort.
      uniq.
      each do |subject|
      log_debug("order_subjects") {subject.to_ntriples}
      subjects << subject
      seen[subject] = true
    end
  end
  log_debug {"subjects2: #{subjects.inspect}"}

  # Mark as seen lists that are part of another list
  @lists.values.map(&:statements).
    flatten.each do |st|
      seen[st.object] if @lists.has_key?(st.object)
    end

  # Sort subjects by resources over bnodes, ref_counts and the subject URI itself
  recursable = @subjects.keys.
    select {|s| !seen.include?(s)}.
    map {|r| [r.node? ? 1 : 0, ref_count(r), r]}.
    sort
  
  log_debug {"subjects3: #{subjects.inspect}"}
  subjects += recursable.map{|r| r.last}
  log_debug {"subjects4: #{subjects.inspect}"}
  subjects
end

#predicate_orderArray<URI> (protected)

Defines order of predicates to to emit at begninning of a resource description. Defaults to [rdf:type, rdfs:label, dc:title]

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 299

def predicate_order; [RDF.type, RDF::RDFS.label, RDF::URI("http://purl.org/dc/terms/title")]; end

#preprocessObject (protected)

Perform any preprocessing of statements required



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 349

def preprocess
  # Load defined prefixes
  (@options[:prefixes] || {}).each_pair do |k, v|
    @uri_to_prefix[v.to_s] = k
  end
  @options[:prefixes] = {}  # Will define actual used when matched

  prefix(nil, @options[:default_namespace]) if @options[:default_namespace]

  @graph.each {|statement| preprocess_statement(statement)}
end

#preprocess_statement(statement) ⇒ Object (protected)

Perform any statement preprocessing required. This is used to perform reference counts and determine required prefixes.

Parameters:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 364

def preprocess_statement(statement)
  #log_debug {"preprocess: #{statement.inspect}"}
  references = ref_count(statement.object) + 1
  @references[statement.object] = references
  @subjects[statement.subject] = true

  # Collect lists
  if statement.predicate == RDF.first
    @lists[statement.subject] = RDF::List.new(subject: statement.subject, graph: graph)
  end

  if statement.object == RDF.nil || statement.subject == RDF.nil
    # Add an entry for the list tail
    @lists[RDF.nil] ||= RDF::List[]
  end

  # Pre-fetch qnames, to fill prefixes
  get_qname(statement.subject)
  get_qname(statement.predicate)
  get_qname(statement.object)
  get_qname(statement.object.datatype) if statement.object.literal? && statement.object.datatype

  @references[statement.predicate] = ref_count(statement.predicate) + 1
end

#quoted(string) ⇒ String (protected)

Use single- or multi-line quotes. If literal contains \t, \n, or \r, use a multiline quote, otherwise, use a single-line

Parameters:

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 417

def quoted(string)
  if string.to_s.match(/[\t\n\r]/)
    string = string.gsub('\\', '\\\\\\\\').gsub('"""', '\\"""')
    %("""#{string}""")
  else
    "\"#{escaped(string)}\""
  end
end

#ref_count(node) ⇒ Integer (protected)

Return the number of times this node has been referenced in the object position

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 391

def ref_count(node)
  @references.fetch(node, 0)
end

#relativize(uri) ⇒ String (protected)

If base_uri is defined, use it to try to make uri relative

Parameters:

  • uri (#to_s)

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 287

def relativize(uri)
  uri = uri.to_s
  base_uri ? uri.sub(base_uri.to_s, "") : uri
end

#resetObject (protected)

Reset internal helper instance variables



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 403

def reset
  @depth = 0
  @lists = {}

  @references = {}
  @serialized = {}
  @subjects = {}
end

#sort_properties(properties) ⇒ Array<String>

Take a hash from predicate uris to lists of values. Sort the lists of values. Return a sorted list of properties.

Parameters:

  • properties (Hash{String => Array<Resource>})

    A hash of Property to Resource mappings

Returns:

  • (Array<String>)

    ] Ordered list of properties. Uses predicate_order.



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 207

def sort_properties(properties)
  # Make sorted list of properties
  prop_list = []
  
  predicate_order.each do |prop|
    next unless properties[prop.to_s]
    prop_list << prop.to_s
  end
  
  properties.keys.sort.each do |prop|
    next if prop_list.include?(prop.to_s)
    prop_list << prop.to_s
  end
  
  log_debug {"sort_properties: #{prop_list.join(', ')}"}
  prop_list
end

#start_documentObject (protected)

Output @base and @prefix definitions



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 275

def start_document
  @output.write("#{indent}@base <#{base_uri}> .\n") unless base_uri.to_s.empty?
  
  log_debug {"start_document: #{prefixes.inspect}"}
  prefixes.keys.sort_by(&:to_s).each do |prefix|
    @output.write("#{indent}@prefix #{prefix}: <#{prefixes[prefix]}> .\n")
  end
end

#top_classesArray<URI> (protected)

Defines rdf:type of subjects to be emitted at the beginning of the graph. Defaults to rdfs:Class

Returns:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 294

def top_classes; [RDF::RDFS.Class]; end

#write_epilogue

This method returns an undefined value.

Outputs the N3 representation of all stored triples.

See Also:



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 139

def write_epilogue
  @max_depth = @options[:max_depth] || 3
  @base_uri = RDF::URI(@options[:base_uri])

  self.reset

  log_debug {"\nserialize: graph: #{@graph.size}"}

  preprocess
  start_document

  order_subjects.each do |subject|
    unless is_done?(subject)
      statement(subject)
    end
  end

  super
end

#write_triple(subject, predicate, object)

This method is abstract.

This method returns an undefined value.

Addes a triple to be serialized

Parameters:

  • subject (RDF::Resource)
  • predicate (RDF::URI)
  • object (RDF::Value)

Raises:

  • (NotImplementedError)

    unless implemented in subclass



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# File 'vendor/bundler/ruby/2.5.0/bundler/gems/rdf-n3-eeb7e2ca9463/lib/rdf/n3/writer.rb', line 130

def write_triple(subject, predicate, object)
  @graph.insert(RDF::Statement(subject, predicate, object))
end