Class: RDF::Turtle::Writer

Inherits:
Writer
  • Object
show all
Includes:
StreamingWriter
Defined in:
lib/rdf/turtle/writer.rb

Overview

A Turtle serialiser

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

Serializing RDF graph into an Turtle file

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

Serializing RDF statements into an Turtle file

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

Serializing RDF statements into an Turtle string

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

Serializing RDF statements to a string in streaming mode

RDF::Turtle::Writer.buffer(stream:  true) do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Creating @base and @prefix definitions in output

RDF::Turtle::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

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from StreamingWriter

#stream_epilogue, #stream_prologue, #stream_statement

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

  • :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.

  • :stream (Boolean) — default: false —

    Do not attempt to optimize graph presentation, suitable for streaming large graphs.

  • :default_namespace (String) — default: nil —

    URI to use as default namespace, same as ‘prefixes`

  • :unique_bnodes (Boolean) — default: false —

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

  • :literal_shorthand (Boolean) — default: true —

    Attempt to use Literal shorthands fo numbers and boolean values

Yields:

  • (writer) —

    ‘self`

  • (writer)

Yield Parameters:

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

Yield Returns:

  • (void) 


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# File 'lib/rdf/turtle/writer.rb', line 97

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

Instance Attribute Details

#graph ⇒ Graph

Returns Graph of statements serialized.

Returns:

  • (Graph) —

    Graph of statements serialized



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# File 'lib/rdf/turtle/writer.rb', line 63

def graph
  @graph
end

Instance Method Details

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

Returns the N-Triples representation of a literal.

Parameters:

  • literal (RDF::Literal, String, #to_s)
  • options (Hash{Symbol => Object}) (defaults to: {})

Returns:

  • (String) 


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# File 'lib/rdf/turtle/writer.rb', line 246

def format_literal(literal, options = {})
  literal = literal.dup.canonicalize! if @options[:canonicalize]
  case literal
  when RDF::Literal
    case @options[:literal_shorthand] && literal.valid? ? literal.datatype : false
    when RDF::XSD.boolean, RDF::XSD.integer, RDF::XSD.decimal
      literal.canonicalize.to_s
    when RDF::XSD.double
      literal.canonicalize.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 representation of a blank node.

Parameters:

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

Returns:

  • (String) 


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# File 'lib/rdf/turtle/writer.rb', line 284

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

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

Returns the Turtle representation of a URI reference.

Parameters:

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

Returns:

  • (String) 


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# File 'lib/rdf/turtle/writer.rb', line 272

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

#get_pname(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 'lib/rdf/turtle/writer.rb', line 178

def get_pname(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

  pname = case
  when @uri_to_pname.has_key?(uri)
    return @uri_to_pname[uri]
  when u = @uri_to_prefix.keys.sort_by {|u| u.length}.reverse.detect {|u| uri.index(u.to_s) == 0}
    # Use a defined prefix
    prefix = @uri_to_prefix[u]
    unless u.to_s.empty?
      prefix(prefix, u) unless u.to_s.empty?
      debug("get_pname") {"add prefix #{prefix.inspect} => #{u}"}
      uri.sub(u.to_s, "#{prefix}:")
    end
  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
    debug("get_pname") {"add standard prefix #{prefix.inspect} => #{vocab.to_uri}"}
    uri.sub(vocab.to_uri.to_s, "#{prefix}:")
  else
    nil
  end
  
  # Make sure pname is a valid pname
  if pname
    md = Terminals::PNAME_LN.match(pname) || Terminals::PNAME_NS.match(pname)
    pname = nil unless md.to_s.length == pname.length
  end

  @uri_to_pname[uri] = pname
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 'lib/rdf/turtle/writer.rb', line 222

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
  
  debug("sort_properties") {prop_list.join(', ')}
  prop_list
end

#write_epilogue ⇒ void

This method returns an undefined value.

Outputs the Turtle representation of all stored triples.

See Also:



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# File 'lib/rdf/turtle/writer.rb', line 153

def write_epilogue
  case
  when @options[:stream]
    stream_epilogue
  else
    @max_depth = @options[:max_depth] || 3

    self.reset

    debug("\nserialize") {"graph: #{@graph.size}"}

    preprocess
    start_document

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

#write_prologue ⇒ void

This method returns an undefined value.

Write out declarations



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# File 'lib/rdf/turtle/writer.rb', line 140

def write_prologue
  case
  when @options[:stream]
    stream_prologue
  else
  end
end

#write_statement(statement) ⇒ void

This method returns an undefined value.

Adds a statement to be serialized

Parameters:

  • statement (RDF::Statement) 


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# File 'lib/rdf/turtle/writer.rb', line 117

def write_statement(statement)
  case
  when @options[:stream]
    stream_statement(statement)
  else
    # Add to local graph and output in epilogue
    @graph.insert(statement)
  end
end

#write_triple(subject, predicate, object) ⇒ void

This method returns an undefined value.

Adds a triple to be serialized

Parameters:

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


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# File 'lib/rdf/turtle/writer.rb', line 133

def write_triple(subject, predicate, object)
  write_statement(Statement.new(subject, predicate, object))
end