Class: RDF::Node

Inherits:
Object
  • Object
show all
Includes:
Resource
Defined in:
lib/rdf/model/node.rb

Overview

An RDF blank node, also known as an anonymous or unlabeled node.

Examples:

Creating a blank node with an implicit identifier

bnode = RDF::Node.new

Creating a blank node with an UUID identifier

bnode = RDF::Node.uuid
bnode.to_s #=> "_:504c0a30-0d11-012d-3f50-001b63cac539"

Constant Summary collapse

CACHE_SIZE =
Note:

caching interned nodes means that two different invocations using the same symbol will result in the same node, which may not be appropriate depending on the graph from which it is used. RDF requires that bnodes with the same label are, in fact, different bnodes, unless they are used within the same document.

Defines the maximum number of interned Node references that can be held cached in memory at any one time.

-1 # unlimited by default

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Resource

new, #resource?

Methods included from Term

#<=>, #compatible?, #term?, #to_base, #to_term

Methods included from Value

#canonicalize, #canonicalize!, #constant?, #graph?, #inspect, #inspect!, #invalid?, #iri?, #list?, #literal?, #resource?, #start_with?, #statement?, #term?, #to_nquads, #to_ntriples, #to_rdf, #to_term, #type_error, #uri?, #valid?, #validate!, #variable?

Constructor Details

#initialize(id = nil) ⇒ Node

Returns a new instance of Node.

Parameters:

  • id (#to_s) (defaults to: nil) 


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# File 'lib/rdf/model/node.rb', line 81

def initialize(id = nil)
  id = nil if id.to_s.empty?
  @id = (id || "g#{__id__.to_i.abs}").to_s.freeze
end

Instance Attribute Details

#id ⇒ String

Returns:



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# File 'lib/rdf/model/node.rb', line 77

def id
  @id
end

#original ⇒ RDF::Node

Originally instantiated node, if any

Returns:



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# File 'lib/rdf/model/node.rb', line 74

def original
  @original
end

Class Method Details

.cache ⇒ RDF::Util::Cache

Returns:



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# File 'lib/rdf/model/node.rb', line 25

def self.cache
  require 'rdf/util/cache' unless defined?(::RDF::Util::Cache)
  @cache ||= RDF::Util::Cache.new(CACHE_SIZE)
end

.intern(id) ⇒ RDF::Node

Alias for RDF::Node.new, at the moment.

Parameters:

Returns:

Since:

  • 0.2.0



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# File 'lib/rdf/model/node.rb', line 55

def self.intern(id)
  (cache[(id = id.to_s).to_sym] ||= self.new(id)).freeze
end

.uuid(format: :default) ⇒ RDF::Node

Returns a blank node with a random UUID-based identifier.

(Depends on availability of either uuid or uuidtools gems).

Formats supported by the UUID generator:

* `:default` Produces 36 characters, including hyphens separating the UUID value parts
* `:compact` Produces a 32 digits (hexadecimal) value with no hyphens
* `:urn` Adds the prefix urn:uuid: to the default format

Requires that the uuid gem be loadable to use format

Parameters:

  • format (:default, :compact) (defaults to: :default) —

    (:default)

Returns:



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# File 'lib/rdf/model/node.rb', line 43

def self.uuid(format: :default)
  uuid = RDF::Util::UUID.generate(format: format)
  self.new(uuid)
end

Instance Method Details

#==(other) ⇒ Boolean Also known as: ===

Checks whether this blank node is equal to other (type checking).

In this case, different nodes having the same id are considered the same.

Per SPARQL data-r2/expr-equal/eq-2-2, numeric can’t be compared with other types

Parameters:

  • other (Object)

Returns:

  • (Boolean)

See Also:



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# File 'lib/rdf/model/node.rb', line 141

def ==(other)
  if other.is_a?(Literal)
    # If other is a Literal, reverse test to consolodate complex type checking logic
    other == self
  else
    other.respond_to?(:node?) && other.node? &&
      self.hash == other.to_term.hash &&
      other.respond_to?(:id) && @id == other.to_term.id
  end
end

#anonymous? ⇒ Boolean Also known as: unlabeled?

Returns true.

Returns:

  • (Boolean) 


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# File 'lib/rdf/model/node.rb', line 98

def anonymous?
  true
end

#dup ⇒ RDF::Node

Override #dup to remember original object. This allows .eql? to determine that two nodes are the same thing, and not different nodes instantiated with the same identifier.

Returns:



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# File 'lib/rdf/model/node.rb', line 65

def dup
  node = super
  node.original = self.original || self
  node
end

#eql?(other) ⇒ Boolean

Determines if self is the same term as other.

In this case, nodes must be the same object

Parameters:

Returns:

  • (Boolean) 


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# File 'lib/rdf/model/node.rb', line 127

def eql?(other)
  other.is_a?(RDF::Node) && (self.original || self).equal?(other.original || other)
end

#hash ⇒ Integer

Returns a hash code for this blank node.

Returns:

  • (Integer) 


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# File 'lib/rdf/model/node.rb', line 116

def hash
  @id.hash
end

#labeled? ⇒ Boolean

Returns false.

Returns:

  • (Boolean) 


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# File 'lib/rdf/model/node.rb', line 108

def labeled?
  !unlabeled?
end

#make_unique! ⇒ self

Make this term identifier unique, if it is found to be shared with another node having the same identifier

Returns:

  • (self) 


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# File 'lib/rdf/model/node.rb', line 164

def make_unique!
  @id = to_unique_base[2..-1]
  self
end

#node? ⇒ Boolean

Returns true.

Returns:

  • (Boolean) 


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# File 'lib/rdf/model/node.rb', line 90

def node?
  true
end

#to_s ⇒ String

Returns a string representation of this blank node.

Returns:



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# File 'lib/rdf/model/node.rb', line 173

def to_s
  "_:%s" % @id.to_s
end

#to_sym ⇒ Symbol

Returns a symbol representation of this blank node.

Returns:

  • (Symbol)

Since:

  • 0.2.0



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# File 'lib/rdf/model/node.rb', line 182

def to_sym
  @id.to_s.to_sym
end

#to_unique_base ⇒ String

Returns a representation of this node independent of any identifier used to initialize it

Returns:



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# File 'lib/rdf/model/node.rb', line 157

def to_unique_base
  original ? original.to_unique_base :  "_:g#{__id__.to_i.abs}"
end