Class: RDF::Writer Abstract

Inherits:
Object
  • Object
show all
Extended by:
Enumerable, Util::Aliasing::LateBound
Includes:
Writable
Defined in:
lib/rdf/writer.rb

Overview

This class is abstract.

The base class for RDF serializers.

Examples:

Loading an RDF writer implementation

require 'rdf/ntriples'

Iterating over known RDF writer classes

RDF::Writer.each { |klass| puts klass.name }

Obtaining an RDF writer class

RDF::Writer.for(:ntriples)     #=> RDF::NTriples::Writer
RDF::Writer.for("spec/data/output.nt")
RDF::Writer.for(:file_name      => "spec/data/output.nt")
RDF::Writer.for(:file_extension => "nt")
RDF::Writer.for(:content_type   => "text/plain")

Instantiating an RDF writer class

RDF::Writer.for(:ntriples).new($stdout) { |writer| ... }

Serializing RDF statements into a file

RDF::Writer.open("spec/data/output.nt") do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

Serializing RDF statements into a string

RDF::Writer.for(:ntriples).buffer do |writer|
  graph.each_statement do |statement|
    writer << statement
  end
end

See Also:

Direct Known Subclasses

NTriples::Writer

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Util::Aliasing::LateBound

alias_method

Methods included from Writable

#<<, #insert, #writable?

Constructor Details

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

Initializes the writer.

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 (not supported by all writers)

Yields:

  • (writer) —

    ‘self`

Yield Parameters:

Yield Returns:

  • (void) 


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# File 'lib/rdf/writer.rb', line 198

def initialize(output = $stdout, options = {}, &block)
  @output, @options = output, options.dup
  @nodes, @node_id  = {}, 0

  if block_given?
    write_prologue
    case block.arity
      when 1 then block.call(self)
      else instance_eval(&block)
    end
    write_epilogue
  end
end

Instance Attribute Details

#options ⇒ Hash (readonly)

Any additional options for this writer.

Returns:

  • (Hash)

Since:

  • 0.2.2



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# File 'lib/rdf/writer.rb', line 217

def options
  @options
end

Class Method Details

.buffer(*args) {|writer| ... } ⇒ String

Buffers output into a string buffer.

Yields:

  • (writer)

Yield Parameters:

Yield Returns:

  • (void)

Returns:

  • (String) 


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# File 'lib/rdf/writer.rb', line 139

def self.buffer(*args, &block)
  StringIO.open do |buffer|
    self.new(buffer, *args) { |writer| block.call(writer) }
    buffer.string
  end
end

.dump(data, io = nil, options = {}) ⇒ void

This method returns an undefined value.

Parameters:

  • data (RDF::Enumerable, #each) —

    the graph or repository to dump

  • io (IO, File) (defaults to: nil) —

    the output stream or file to write to

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

    passed to #initialize or buffer



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# File 'lib/rdf/writer.rb', line 113

def self.dump(data, io = nil, options = {})
  io = File.open(io, 'w') if io.is_a?(String)
  method = data.respond_to?(:each_statement) ? :each_statement : :each
  if io
    new(io, options) do |writer|
      data.send(method) do |statement|
        writer << statement
      end
      writer.flush
    end
  else
    buffer(options) do |writer|
      data.send(method) do |statement|
        writer << statement
      end
    end
  end
end

.each {|klass| ... } ⇒ Enumerator

Enumerates known RDF writer classes.

Yields:

  • (klass)

Yield Parameters:

  • klass (Class)

Yield Returns:

  • (void) —

    ignored

Returns:



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# File 'lib/rdf/writer.rb', line 50

def self.each(&block)
  @@subclasses.each(&block)
end

.for(format) ⇒ Class .for(filename) ⇒ Class .for(options = {}) ⇒ Class

Finds an RDF writer class based on the given criteria.

Overloads:

  • .for(format) ⇒ Class

    Finds an RDF writer class based on a symbolic name.

    Parameters:

    • format (Symbol)

    Returns:

    • (Class)
  • .for(filename) ⇒ Class

    Finds an RDF writer class based on a file name.

    Parameters:

    • filename (String)

    Returns:

    • (Class)
  • .for(options = {}) ⇒ Class

    Finds an RDF writer class based on various options.

    Parameters:

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

    Options Hash (options):

    • :file_name (String, #to_s) — default: nil
    • :file_extension (Symbol, #to_sym) — default: nil
    • :content_type (String, #to_s) — default: nil

    Returns:

    • (Class)

Returns:

  • (Class) 


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# File 'lib/rdf/writer.rb', line 79

def self.for(options = {})
  options = options.merge(:has_writer => true) if options.is_a?(Hash)
  if format = self.format || Format.for(options)
    format.writer
  end
end

.format(klass = nil) ⇒ Class Also known as: format_class

Retrieves the RDF serialization format class for this writer class.

Returns:

  • (Class) 


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# File 'lib/rdf/writer.rb', line 90

def self.format(klass = nil)
  if klass.nil?
    Format.each do |format|
      if format.writer == self
        return format
      end
    end
    nil # not found
  end
end

.open(filename, options = {}, &block) ⇒ RDF::Writer

Writes output to the given ‘filename`.

Parameters:

  • filename (String, #to_s)
  • options (Hash{Symbol => Object}) (defaults to: {}) —

    any additional options (see #initialize and Format.for)

Options Hash (options):

  • :format (Symbol) — default: nil

Returns:



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# File 'lib/rdf/writer.rb', line 154

def self.open(filename, options = {}, &block)
  File.open(filename, 'wb') do |file|
    format_options = options.dup
    format_options[:file_name] ||= filename
    self.for(options[:format] || format_options).new(file, options, &block)
  end
end

.to_sym ⇒ Symbol

Returns a symbol appropriate to use with RDF::Writer.for()

Returns:

  • (Symbol) 


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# File 'lib/rdf/writer.rb', line 165

def self.to_sym
  elements = self.to_s.split("::")
  sym = elements.pop
  sym = elements.pop if sym == 'Writer'
  sym.downcase.to_s.to_sym
end

Instance Method Details

#base_uri ⇒ Hash{Symbol => RDF::URI}

Returns the base URI used for this writer.

Examples:

reader.prefixes[:dc]  #=> RDF::URI('http://purl.org/dc/terms/')

Returns:

Since:

  • 0.3.4



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# File 'lib/rdf/writer.rb', line 227

def base_uri
  @options[:base_uri]
end

#flush ⇒ void Also known as: flush!

This method returns an undefined value.

Flushes the underlying output buffer.



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# File 'lib/rdf/writer.rb', line 285

def flush
  @output.flush if @output.respond_to?(:flush)
  self
end

#format_list(value, options = {}) ⇒ String

This method is abstract.

Parameters:

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

Returns:

  • (String)

Since:

  • 0.2.3



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# File 'lib/rdf/writer.rb', line 411

def format_list(value, options = {})
  format_term(value.subject, options)
end

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

This method is abstract.

Parameters:

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

Returns:

  • (String)

Raises:

  • (NotImplementedError) —

    unless implemented in subclass



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# File 'lib/rdf/writer.rb', line 401

def format_literal(value, options = {})
  raise NotImplementedError.new("#{self.class}#format_literal") # override in subclasses
end

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

This method is abstract.

Parameters:

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

Returns:

  • (String)

Raises:

  • (NotImplementedError) —

    unless implemented in subclass



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# File 'lib/rdf/writer.rb', line 381

def format_node(value, options = {})
  raise NotImplementedError.new("#{self.class}#format_node") # override in subclasses
end

#format_term(term, options = {}) ⇒ String Also known as: format_value

Parameters:

Returns:

  • (String)

Since:

  • 0.3.0



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# File 'lib/rdf/writer.rb', line 363

def format_term(term, options = {})
  case term
    when String       then format_literal(RDF::Literal(term, options), options)
    when RDF::List    then format_list(term, options)
    when RDF::Literal then format_literal(term, options)
    when RDF::URI     then format_uri(term, options)
    when RDF::Node    then format_node(term, options)
    else nil
  end
end

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

This method is abstract.

Parameters:

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

Returns:

  • (String)

Raises:

  • (NotImplementedError) —

    unless implemented in subclass



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# File 'lib/rdf/writer.rb', line 391

def format_uri(value, options = {})
  raise NotImplementedError.new("#{self.class}#format_uri") # override in subclasses
end

#prefix(name, uri) ⇒ RDF::URI #prefix(name) ⇒ RDF::URI Also known as: prefix!

Defines the given named URI prefix for this writer.

Examples:

Defining a URI prefix

writer.prefix :dc, RDF::URI('http://purl.org/dc/terms/')

Returning a URI prefix

writer.prefix(:dc)    #=> RDF::URI('http://purl.org/dc/terms/')

Overloads:

  • #prefix(name, uri) ⇒ RDF::URI

    Parameters:

    • name (Symbol, #to_s)
    • uri (RDF::URI, #to_s)
  • #prefix(name) ⇒ RDF::URI

    Parameters:

    • name (Symbol, #to_s)

Returns:



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# File 'lib/rdf/writer.rb', line 275

def prefix(name, uri = nil)
  name = name.to_s.empty? ? nil : (name.respond_to?(:to_sym) ? name.to_sym : name.to_s.to_sym)
  uri.nil? ? prefixes[name] : prefixes[name] = uri
end

#prefixes ⇒ Hash{Symbol => RDF::URI}

Returns the URI prefixes currently defined for this writer.

Examples:

writer.prefixes[:dc]  #=> RDF::URI('http://purl.org/dc/terms/')

Returns:

Since:

  • 0.2.2



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# File 'lib/rdf/writer.rb', line 239

def prefixes
  @options[:prefixes] ||= {}
end

#prefixes=(prefixes) ⇒ Hash{Symbol => RDF::URI}

Defines the given URI prefixes for this writer.

Examples:

writer.prefixes = {
  :dc => RDF::URI('http://purl.org/dc/terms/'),
}

Parameters:

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/writer.rb', line 254

def prefixes=(prefixes)
  @options[:prefixes] = prefixes
end

#to_sym ⇒ Symbol

Returns a symbol appropriate to use with RDF::Writer.for()

Returns:

  • (Symbol) 


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# File 'lib/rdf/writer.rb', line 175

def to_sym
  self.class.to_sym
end

#write_comment(text) ⇒ void

This method is abstract.

This method returns an undefined value.

Returns ‘self`.

Parameters:

  • text (String) 


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# File 'lib/rdf/writer.rb', line 309

def write_comment(text)
  self
end

#write_epilogue ⇒ void

This method is abstract.

This method returns an undefined value.

Returns ‘self`.



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# File 'lib/rdf/writer.rb', line 301

def write_epilogue
  self
end

#write_graph(graph) ⇒ void

Deprecated.

replace by ‘RDF::Writable#insert_graph`

This method returns an undefined value.

Returns ‘self`.

Parameters:



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# File 'lib/rdf/writer.rb', line 317

def write_graph(graph)
  graph.each_triple { |*triple| write_triple(*triple) }
  self
end

#write_prologue ⇒ void

This method is abstract.

This method returns an undefined value.

Returns ‘self`.



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# File 'lib/rdf/writer.rb', line 294

def write_prologue
  self
end

#write_statement(statement) ⇒ void Also known as: insert_statement

This method returns an undefined value.

Returns ‘self`.

Parameters:



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# File 'lib/rdf/writer.rb', line 334

def write_statement(statement)
  write_triple(*statement.to_triple)
  self
end

#write_statements(*statements) ⇒ void

Deprecated.

replace by ‘RDF::Writable#insert_statements`

This method returns an undefined value.

Returns ‘self`.

Parameters:



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# File 'lib/rdf/writer.rb', line 326

def write_statements(*statements)
  statements.flatten.each { |statement| write_statement(statement) }
  self
end

#write_triple(subject, predicate, object) ⇒ void

This method is abstract.

This method returns an undefined value.

Returns ‘self`.

Parameters:

Raises:

  • (NotImplementedError) —

    unless implemented in subclass



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# File 'lib/rdf/writer.rb', line 355

def write_triple(subject, predicate, object)
  raise NotImplementedError.new("#{self.class}#write_triple") # override in subclasses
end

#write_triples(*triples) ⇒ void

This method returns an undefined value.

Returns ‘self`.

Parameters:



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# File 'lib/rdf/writer.rb', line 343

def write_triples(*triples)
  triples.each { |triple| write_triple(*triple) }
  self
end