Class: RDF::Format Abstract

Inherits:
Object
  • Object
show all
Extended by:
Enumerable
Defined in:
lib/rdf/format.rb

Overview

This class is abstract.

The base class for RDF serialization formats.

Examples:

Loading an RDF serialization format implementation

require 'rdf/ntriples'

Iterating over known RDF serialization formats

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

Getting a serialization format class

RDF::Format.for(:ntriples)     #=> RDF::NTriples::Format
RDF::Format.for("etc/doap.nt")
RDF::Format.for(file_name: "etc/doap.nt")
RDF::Format.for(file_extension: "nt")
RDF::Format.for(content_type: "application/n-triples")

Obtaining serialization format MIME types

RDF::Format.content_types      #=> {"application/n-triples" => [RDF::NTriples::Format]}

Obtaining serialization format file extension mappings

RDF::Format.file_extensions    #=> {nt: [RDF::NTriples::Format]}

Defining a new RDF serialization format class

class RDF::NTriples::Format < RDF::Format
  content_type     'application/n-triples',
                   extension: :nt,
                   uri: RDF::URI("http://www.w3.org/ns/formats/N-Triples")
  content_encoding 'utf-8'

  reader RDF::NTriples::Reader
  writer RDF::NTriples::Writer
end

Instantiating an RDF reader or writer class (1)

RDF::Format.for(:ntriples).reader.new($stdin)  { |reader| ... }
RDF::Format.for(:ntriples).writer.new($stdout) { |writer| ... }

Instantiating an RDF reader or writer class (2)

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

See Also:

Class Method Summary collapse

Class Method Details

.accept_type ⇒ Array<String>

Returns an array of values appropriate for an Accept header. Same as self.content_type, if no parameter is given when defined.

Returns:

  • (Array<String>) 


535
536
537
 
# File 'lib/rdf/format.rb', line 535

def self.accept_type
  @@accept_types.map {|t, formats| t if formats.include?(self)}.compact
end

.accept_types ⇒ Array<String>

Returns the set of content types with quality for available RDF::Reader subclasses.

Examples:


accept_types = RDF::Format.accept_types
# => %w(text/html;q=0.5 text/turtle ...)

Returns:

  • (Array<String>) 


275
276
277
 
# File 'lib/rdf/format.rb', line 275

def self.accept_types
  reader_symbols.flat_map {|s| RDF::Format.for(s).accept_type}.uniq
end

.cli_commands ⇒ Hash{Symbol => {description: String, lambda: Lambda(Array, Hash)}}

Hash of CLI commands appropriate for this format

Returns:

  • (Hash{Symbol => {description: String, lambda: Lambda(Array, Hash)}}) 


434
435
436
 
# File 'lib/rdf/format.rb', line 434

def self.cli_commands
  {}
end

.content_encoding(encoding = nil) (protected)

This method returns an undefined value.

Defines the content encoding for this RDF serialization format.

When called without an encoding, it returns the currently defined content encoding for this format

Parameters:

  • encoding (#to_sym) (defaults to: nil) 


584
585
586
587
 
# File 'lib/rdf/format.rb', line 584

def self.content_encoding(encoding = nil)
  @@content_encoding[self] = encoding.to_sym if encoding
  @@content_encoding[self] || "utf-8"
end

.content_type(type, options) .content_type ⇒ Array<String>

Retrieves or defines MIME content types for this RDF serialization format.

Overloads:

  • .content_type(type, options)

    This method returns an undefined value.

    Retrieves or defines the MIME content type for this RDF serialization format.

    Optionally also defines alias MIME content types for this RDF serialization format.

    Optionally also defines a file extension, or a list of file extensions, that should be mapped to the given MIME type and handled by this class.

    Optionally, both type, alias, and aliases, may be parameterized for expressing quality.

    content_type "text/html;q=0.4"

    Parameters:

    • type (String)
    • options (Hash{Symbol => Object})

    Options Hash (options):

    • :alias (String) — default: nil
    • :aliases (Array<String>) — default: nil
    • :extension (Symbol) — default: nil
    • :extensions (Array<Symbol>) — default: nil
    • :uri (URI) — default: nil
  • .content_type ⇒ Array<String>

    Retrieves the MIME content types for this RDF serialization format.

    The return is an array where the first element is the cannonical MIME type for the format and following elements are alias MIME types.

    Returns:

    • (Array<String>) 


493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
 
# File 'lib/rdf/format.rb', line 493

def self.content_type(type = nil, options = {})
  if type.nil?
    [@@content_type[self], @@content_types.map {
      |ct, cl| (cl.include?(self) && ct != @@content_type[self]) ?  ct : nil }].flatten.compact
  else
    accept_type, type = type, type.split(';').first
    @@content_type[self] = type
    @@content_types[type] ||= []
    @@content_types[type] << self unless @@content_types[type].include?(self)

    @@accept_types[accept_type] ||= []
    @@accept_types[accept_type] << self unless @@accept_types[accept_type].include?(self)

    if extensions = (options[:extension] || options[:extensions])
      extensions = Array(extensions).map(&:to_sym)
      extensions.each do |ext|
        @@file_extensions[ext] ||= []
        @@file_extensions[ext] << self unless @@file_extensions[ext].include?(self)
      end
    end
    if aliases = (options[:alias] || options[:aliases])
      aliases = Array(aliases).each do |a|
        aa = a.split(';').first
        @@accept_types[a] ||= []
        @@accept_types[a] << self unless @@accept_types[a].include?(self)

        @@content_types[aa] ||= []
        @@content_types[aa] << self unless @@content_types[aa].include?(self)
      end
    end
    # URI identifying this format
    if uri = options[:uri]
      @@uris[RDF::URI(uri)] = self
    end
  end
end

.content_types ⇒ Hash{String => Array<Class>}

Returns MIME content types for known RDF serialization formats.

Examples:

retrieving a list of supported Mime types


RDF::Format.content_types.keys

Returns:

  • (Hash{String => Array<Class>}) 


211
212
213
 
# File 'lib/rdf/format.rb', line 211

def self.content_types
  @@content_types
end

.detect(sample) ⇒ Boolean

Use a text sample to detect the format of an input file. Sub-classes implement a matcher sufficient to detect probably format matches, including disambiguating between other similar formats.

Used to determine format class from loaded formats by for when a match cannot be unambigiously found otherwise.

Examples:

RDF::NTriples::Format.detect("<a> <b> <c> .") #=> true

Parameters:

  • sample (String) —

    Beginning several bytes (~ 1K) of input.

Returns:

  • (Boolean) 


451
452
453
 
# File 'lib/rdf/format.rb', line 451

def self.detect(sample)
  false
end

.each(file_name: nil, file_extension: nil, content_type: nil, has_reader: false, has_writer: false, sample: nil, all_if_none: true, **options) {|klass| ... } ⇒ Enumerator

Enumerates known RDF serialization format classes.

Given options from for, it returns just those formats that match the specified criteria.

Examples:

finding all formats that have a writer supporting text/html

RDF::Format.each(content_type: 'text/html', has_writer: true).to_a
  #=> RDF::RDFa::Format

Parameters:

  • file_name (String, #to_s) (defaults to: nil) —

    (nil)

  • file_extension (Symbol, #to_sym) (defaults to: nil) —

    (nil)

  • content_type (String, #to_s) (defaults to: nil) —

    (nil) Content type may include wildcard characters, which will select among matching formats. Note that content_type will be taken from a URL opened using Util::File.open_file.

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

    (false) Only return a format having a reader.

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

    (false) Only return a format having a writer.

  • sample (String, Proc) (defaults to: nil) —

    (nil) A sample of input used for performing format detection. If we find no formats, or we find more than one, and we have a sample, we can perform format detection to find a specific format to use, in which case we pick the last one we find

  • all_if_none (Boolean) (defaults to: true) —

    (true) Returns all formats if none match, otherwise no format. Note that having a sample overrides this, and will search through all formats, or all those filtered to find a sample that matches

Yields:

  • (klass)

Yield Parameters:

  • (Class)

Returns:

  • (Enumerator) 


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
 
# File 'lib/rdf/format.rb', line 75

def self.each(file_name: nil,
              file_extension: nil,
              content_type: nil,
              has_reader: false,
              has_writer: false,
              sample: nil,
              all_if_none: true,
              **options,
              &block)
  formats = case
  # Find a format based on the MIME content type:
  when content_type
    # @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.17
    # @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.7
    mime_type = content_type.to_s.split(';').first.to_s # remove any media type parameters

    # Ignore text/plain, a historical encoding for N-Triples, which is
    # problematic in format detection, as many web servers will serve
    # content by default text/plain.
    if (mime_type == 'text/plain' && sample) || mime_type == '*/*'
      # All content types
      @@subclasses
    elsif mime_type.end_with?('/*')
      # All content types that have the first part of the mime-type as a prefix
      prefix = mime_type[0..-3]
      content_types.map do |ct, fmts|
        ct.start_with?(prefix) ? fmts : []
      end.flatten.uniq
    else
      content_types[mime_type]
    end
  # Find a format based on the file name:
  when file_name
    ext = File.extname(RDF::URI(file_name).path.to_s)[1..-1].to_s
    file_extensions[ext.to_sym]
  # Find a format based on the file extension:
  when file_extension
    file_extensions[file_extension.to_sym]
  else
    all_if_none ? @@subclasses : nil
  end || (sample ? @@subclasses : []) # If we can sample, check all classes

  # Subset by available reader or writer
  formats = formats.select do |f|
    has_reader ? f.reader : (has_writer ? f.writer : true)
  end

  # If we have multiple formats and a sample, use that for format detection
  if formats.length != 1 && sample
    sample = case sample
    when Proc then sample.call.to_s
    else sample.dup.to_s
    end.dup.force_encoding(Encoding::ASCII_8BIT)
    # Given a sample, perform format detection across the appropriate formats, choosing the last that matches
    # Return last format that has a positive detection
    formats = formats.select {|f| f.detect(sample)}
  end
  formats.each(&block)
end

.file_extension ⇒ Array<String>

Retrieves file extensions for this RDF serialization format.

The return is an array where the first element is the cannonical file extension for the format and following elements are alias file extensions.

Returns:

  • (Array<String>) 


546
547
548
 
# File 'lib/rdf/format.rb', line 546

def self.file_extension
  @@file_extensions.map {|ext, formats| ext if formats.include?(self)}.compact
end

.file_extensions ⇒ Hash{Symbol => Array<Class>}

Returns file extensions for known RDF serialization formats.

Examples:

retrieving a list of supported file extensions


RDF::Format.file_extensions.keys

Returns:

  • (Hash{Symbol => Array<Class>}) 


223
224
225
 
# File 'lib/rdf/format.rb', line 223

def self.file_extensions
  @@file_extensions
end

.for(format) ⇒ Class .for(filename) ⇒ Class .for(options) ⇒ Class

Finds an RDF serialization format class based on the given criteria. If multiple formats are identified, the last one found is returned; this allows descrimination of equivalent formats based on load order.

Overloads:

  • .for(format) ⇒ Class

    Finds an RDF serialization format class based on a symbolic name.

    Parameters:

    • format (Symbol)

    Returns:

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

    Finds an RDF serialization format class based on a file name.

    Parameters:

    Returns:

    • (Class)
  • .for(options) ⇒ Class

    Finds an RDF serialization format class based on various options.

    Content type may include wildcard characters, which will select among matching formats. Note that content_type will be taken from a URL opened using Util::File.open_file.

    Parameters:

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

      ({})

    Options Hash (options):

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

      Only return a format having a reader.

    • :has_writer (Boolean) — default: false —

      Only return a format having a writer.

    • :sample (String) — default: nil —

      A sample of input used for performing format detection. If we find no formats, or we find more than one, and we have a sample, we can perform format detection to find a specific format to use, in which case we pick the last one we find

    Yield Returns:

    • (String) —

      another way to provide a sample, allows lazy for retrieving the sample.

    Returns:

    • (Class)

Returns:

  • (Class) 


169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
 
# File 'lib/rdf/format.rb', line 169

def self.for(*arg, &block)
  case arg.length
  when 0 then arg = nil
  when 1 then arg = arg.first
  else
    raise ArgumentError, "Format.for accepts zero or one argument, got #{arg.length}."
  end

  options =  arg.is_a?(Hash) ? arg : {}
  options = {sample: block}.merge(options) if block_given?
  formats = case arg
  when String, RDF::URI
    # Find a format based on the file name
    self.each(file_name: arg, **options).to_a
  when Symbol
    # Try to find a match based on the full class name
    # We want this to work even if autoloading fails
    classes = self.each(**options).select {|f| f.symbols.include?(arg)}
    if classes.empty?
      classes = case arg
      when :ntriples then [RDF::NTriples::Format]
      when :nquads   then [RDF::NQuads::Format]
      else                []
      end
    end
    classes
  else
    self.each(**options.merge(all_if_none: false)).to_a
  end

  # Return the last detected format
  formats.last
end

.name ⇒ Symbol

Returns a human-readable name for the format. Subclasses should override this to use something difererent than the Class name.

Examples:


RDF::NTriples::Format.name => "N-Triples"

Returns:

  • (Symbol) 


338
339
340
341
342
343
 
# File 'lib/rdf/format.rb', line 338

def self.name
  elements = self.to_s.split("::")
  name = elements.pop
  name = elements.pop if name == 'Format'
  name.to_s
end

.reader(klass) .reader { ... } .reader ⇒ Class Also known as: reader_class

This method returns an undefined value.

Retrieves or defines the reader class for this RDF serialization format.

Overloads:

  • .reader(klass)

    This method returns an undefined value.

    Defines the reader class for this RDF serialization format.

    The class should be a subclass of Reader, or implement the same interface.

    Parameters:

    • klass (Class)
  • .reader { ... }

    This method returns an undefined value.

    Defines the reader class for this RDF serialization format.

    The block should return a subclass of Reader, or a class that implements the same interface. The block won’t be invoked until the reader class is first needed.

    Yields:

    Yield Returns:

    • (Class) —

      klass

  • .reader ⇒ Class

    Retrieves the reader class for this RDF serialization format.

    Returns:

    • (Class) 


375
376
377
378
379
380
381
382
383
384
385
386
 
# File 'lib/rdf/format.rb', line 375

def self.reader(klass = nil, &block)
  case
    when klass
      @@readers[self] = klass
    when block_given?
      @@readers[self] = block
    else
      klass = @@readers[self]
      klass = @@readers[self] = klass.call if klass.is_a?(Proc)
      klass
  end
end

.reader_symbols ⇒ Array<Symbol>

Returns the set of format symbols for available RDF::Reader subclasses.

Examples:


symbols = RDF::Format.reader_symbols
format = RDF::Format.for(symbols.first)

Returns:

  • (Array<Symbol>) 


249
250
251
 
# File 'lib/rdf/format.rb', line 249

def self.reader_symbols
  @@readers.keys.map(&:symbols).flatten.uniq
end

.reader_types ⇒ Array<String>

Returns the set of content types for available RDF::Reader subclasses.

Examples:


content_types = RDF::Format.reader_types
format = RDF::Format.for(content_type: content_types.first)

Returns:

  • (Array<String>) 


262
263
264
 
# File 'lib/rdf/format.rb', line 262

def self.reader_types
  reader_symbols.flat_map {|s| RDF::Format.for(s).content_type}.uniq
end

.require(library) (protected)

This method returns an undefined value.

Defines a required Ruby library for this RDF serialization format.

The given library will be required lazily, i.e. only when it is actually first needed, such as when instantiating a reader or parser instance for this format.

Parameters:

  • library (String, #to_s) 


572
573
574
 
# File 'lib/rdf/format.rb', line 572

def self.require(library)
  (@@requires[self] ||= []) << library.to_s
end

.symbols ⇒ Array<Symbol>

Note:

Individual formats can override this to provide an array of symbols; otherwise, it uses self.to_sym

Returns the set of symbols for a writer appropriate for use with with RDF::Format.for()

Returns:

  • (Array<Symbol>)

See Also:

Since:

  • 2.0



324
325
326
 
# File 'lib/rdf/format.rb', line 324

def self.symbols
  [self.to_sym]
end

.to_sym ⇒ Symbol

Note:

Defaults to the last element of the class name before Format downcased and made a symbol. Individual formats can override this.

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

Returns:

  • (Symbol) 


310
311
312
313
314
315
 
# File 'lib/rdf/format.rb', line 310

def self.to_sym
  elements = self.to_s.split("::")
  sym = elements.pop
  sym = elements.pop if sym == 'Format'
  sym.downcase.to_s.to_sym if sym.is_a?(String)
end

.uri ⇒ URI Also known as: to_uri

Retrieves any format URI defined for this format..

Returns:



554
555
556
 
# File 'lib/rdf/format.rb', line 554

def self.uri
  @@uris.invert[self]
end

.uris ⇒ Hash{Symbol => URI}

Returns the unique URI for the format.

Examples:

retrieving a list of supported file format URIs


RDF::Format.uris.keys

Returns:

  • (Hash{Symbol => URI})

See Also:



236
237
238
 
# File 'lib/rdf/format.rb', line 236

def self.uris
  @@uris
end

.writer(klass) .writer { ... } .writer ⇒ Class Also known as: writer_class

This method returns an undefined value.

Retrieves or defines the writer class for this RDF serialization format.

Overloads:

  • .writer(klass)

    This method returns an undefined value.

    Defines the writer class for this RDF serialization format.

    The class should be a subclass of Writer, or implement the same interface.

    Parameters:

    • klass (Class)
  • .writer { ... }

    This method returns an undefined value.

    Defines the writer class for this RDF serialization format.

    The block should return a subclass of Writer, or a class that implements the same interface. The block won’t be invoked until the writer class is first needed.

    Yields:

    Yield Returns:

    • (Class) —

      klass

  • .writer ⇒ Class

    Retrieves the writer class for this RDF serialization format.

    Returns:

    • (Class) 


418
419
420
421
422
423
424
425
426
427
428
429
 
# File 'lib/rdf/format.rb', line 418

def self.writer(klass = nil, &block)
  case
    when klass
      @@writers[self] = klass
    when block_given?
      @@writers[self] = block
    else
      klass = @@writers[self]
      klass = @@writers[self] = klass.call if klass.is_a?(Proc)
      klass
  end
end

.writer_symbols ⇒ Array<Symbol>

Returns the set of format symbols for available RDF::Writer subclasses.

Examples:


symbols = RDF::Format.writer_symbols
format = RDF::Format.for(symbols.first)

Returns:

  • (Array<Symbol>) 


288
289
290
 
# File 'lib/rdf/format.rb', line 288

def self.writer_symbols
  @@writers.keys.map(&:symbols).flatten.uniq
end

.writer_types ⇒ Array<String>

Returns the set of content types for available RDF::Writer subclasses.

Examples:


content_types = RDF::Format.writer_types
format = RDF::Format.for(content_type: content_types.first)

Returns:

  • (Array<String>) 


301
302
303
 
# File 'lib/rdf/format.rb', line 301

def self.writer_types
  writer_symbols.flat_map {|s| RDF::Format.for(s).content_type}.uniq
end