Class: RDF::Literal

Inherits:
Object
  • Object
show all
Includes:
Term
Defined in:
lib/rdf/model/literal.rb,
lib/rdf/model/literal/date.rb,
lib/rdf/model/literal/time.rb,
lib/rdf/model/literal/token.rb,
lib/rdf/model/literal/double.rb,
lib/rdf/model/literal/boolean.rb,
lib/rdf/model/literal/decimal.rb,
lib/rdf/model/literal/integer.rb,
lib/rdf/model/literal/numeric.rb,
lib/rdf/model/literal/datetime.rb,
lib/rdf/model/literal/temporal.rb

Overview

An RDF literal.

Subclasses of Literal should define DATATYPE and GRAMMAR constants, which are used for identifying the appropriate class to use for a datatype URI and to perform lexical matching on the value.

Literal comparison with other Value instances call Value#type_error, which, returns false. Implementations wishing to have TypeError raised should mix-in TypeCheck. This is required for strict SPARQL conformance.

Specific typed literals may have behavior different from the default implementation. See the following defined sub-classes for specific documentation. Additional sub-classes may be defined, and will interoperate by defining DATATYPE and GRAMMAR constants, in addition other required overrides of RDF::Literal behavior.

In RDF 1.1, all literals are typed, including plain literals and language-tagged strings. Internally, plain literals are given the xsd:string datatype and language-tagged strings are given the rdf:langString datatype. Creating a plain literal, without a datatype or language, will automatically provide the xsd:string datatype; similar for language-tagged strings. Note that most serialization formats will remove this datatype. Code which depends on a literal having the xsd:string datatype being different from a plain literal (formally, without a datatype) may break. However note that the #has_datatype? will continue to return false for plain or language-tagged strings.

RDF 1.2 adds directional language-tagged strings which are effectively a subclass of language-tagged strings contining an additional direction component with value either ltr or rtl for Left-to-Right or Right-to-Left. This determines the general direction of a string when presented in n a user agent, where it might be in conflict with the inherent direction of the leading Unicode code points. Directional language-tagged strings are given the rdf:langString datatype.

Examples:

Creating a plain literal

value = RDF::Literal.new("Hello, world!")
value.plain?                                   #=> true`

Creating a language-tagged string (1)

value = RDF::Literal.new("Hello!", language: :en)
value.language?                                #=> true
value.language                                 #=> :en

Creating a language-tagged string (2)

RDF::Literal.new("Wazup?", language: :"en-US")
RDF::Literal.new("Hej!",   language: :sv)
RDF::Literal.new("¡Hola!", language: :es)

Creating a directional language-tagged string

value = RDF::Literal.new("Hello!", language: :en, direction: :ltr)
value.language?                                #=> true
value.language                                 #=> :en
value.direction?                               #=> true
value.direction                                #=> :ltr

Creating an explicitly datatyped literal

value = RDF::Literal.new("2009-12-31", datatype: RDF::XSD.date)
value.datatype?                                #=> true
value.datatype                                 #=> RDF::XSD.date

Creating an implicitly datatyped literal

value = RDF::Literal.new(Date.today)
value.datatype?                                #=> true
value.datatype                                 #=> RDF::XSD.date

Creating implicitly datatyped literals

RDF::Literal.new(false).datatype               #=> XSD.boolean
RDF::Literal.new(true).datatype                #=> XSD.boolean
RDF::Literal.new(123).datatype                 #=> XSD.integer
RDF::Literal.new(9223372036854775807).datatype #=> XSD.integer
RDF::Literal.new(3.1415).datatype              #=> XSD.double
RDF::Literal.new(Time.now).datatype            #=> XSD.dateTime
RDF::Literal.new(Date.new(2010)).datatype      #=> XSD.date
RDF::Literal.new(DateTime.new(2010)).datatype  #=> XSD.dateTime

See Also:

Direct Known Subclasses

Boolean, Numeric, Temporal, Token

Defined Under Namespace

Classes: Boolean, Date, DateTime, Decimal, Double, Integer, Numeric, Temporal, Time, Token

Constant Summary collapse

TRUE = 
RDF::Literal.new(true)
FALSE = 
RDF::Literal.new(false)
ZERO = 
RDF::Literal.new(0)
XSD_STRING = 
RDF::URI("http://www.w3.org/2001/XMLSchema#string")

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Term

#term?, #terms, #to_base, #to_term

Methods included from Value

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

Constructor Details

#initialize(value, language: nil, datatype: nil, direction: nil, lexical: nil, validate: false, canonicalize: false, **options) ⇒ Literal

Literals without a datatype are given either xsd:string, rdf:langString, or rdf:dirLangString, depending on if there is language and/or direction.

Parameters:

  • value (Object)
  • direction (Symbol) (defaults to: nil) —

    (nil) Initial text direction.

  • language (Symbol) (defaults to: nil) —

    (nil) Language is downcased to ensure proper matching

  • lexical (String) (defaults to: nil) —

    (nil) Supplied lexical representation of this literal, otherwise it comes from transforming value to a string form..

  • datatype (URI) (defaults to: nil) —

    (nil)

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

    (false)

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

    (false)

Raises:

  • (ArgumentError) —

    if there is a language and datatype is no rdf:langString or datatype is rdf:langString and there is no language

See Also:



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# File 'lib/rdf/model/literal.rb', line 190

def initialize(value, language: nil, datatype: nil, direction: nil, lexical: nil, validate: false, canonicalize: false, **options)
  @object   = value.freeze
  @string   = lexical if lexical
  @string   = value if !defined?(@string) && value.is_a?(String)
  @string   = @string.encode(Encoding::UTF_8).freeze if instance_variable_defined?(:@string)
  @object   = @string if instance_variable_defined?(:@string) && @object.is_a?(String)
  @language = language.to_s.downcase.to_sym if language
  @direction = direction.to_s.to_sym if direction
  @datatype = RDF::URI(datatype).freeze if datatype
  @datatype ||= self.class.const_get(:DATATYPE) if self.class.const_defined?(:DATATYPE)
  @datatype ||= if instance_variable_defined?(:@language) && @language &&
                   instance_variable_defined?(:@direction) && @direction
    RDF.dirLangString
  elsif instance_variable_defined?(:@language) && @language
    RDF.langString
  else
    XSD_STRING
  end
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

# ⇒ String (protected)

This method is implemented when the datatype is xsd:string, rdf:langString, or rdf:dirLangString

Returns:

  • (String) 


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# File 'lib/rdf/model/literal.rb', line 603

def method_missing(name, *args)
  case name
  when :to_str
    return to_s if [RDF.langString, RDF.dirLangString, XSD_STRING].include?(@datatype)
  end
  super
end

Instance Attribute Details

#datatype ⇒ URI

Returns The XML Schema datatype URI (optional).

Returns:

  • (URI) —

    The XML Schema datatype URI (optional).



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# File 'lib/rdf/model/literal.rb', line 167

def datatype
  @datatype
end

#direction ⇒ Symbol

Returns The base direction (optional). Implies datatype is rdf:dirLangString.

Returns:

  • (Symbol) —

    The base direction (optional). Implies datatype is rdf:dirLangString.



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

def direction
  @direction
end

#language ⇒ Symbol

Returns The language-tag (optional). Implies datatype is rdf:langString.

Returns:

  • (Symbol) —

    The language-tag (optional). Implies datatype is rdf:langString.



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# File 'lib/rdf/model/literal.rb', line 161

def language
  @language
end

Instance Method Details

#<=>(other) ⇒ Integer

Compares self to other for sorting purposes (with type check).

Parameters:

  • other (Object)

Returns:



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# File 'lib/rdf/model/literal.rb', line 353

def <=>(other)
  case other
  when Literal
    case
    when self.eql?(other)
      0
    when self.language? && other.language?
      # Literals with languages can compare if languages are identical
      self.to_s <=> other.to_s
    when self.simple? && other.simple?
      self.to_s <=> other.to_s
    when !self.valid?
      type_error("#{self.inspect} is invalid") || 0
    when !other.valid?
      type_error("#{other.inspect} is invalid") || 0
    when self.comperable_datatype2?(other)
      self.object <=> other.object
    else
      type_error("#{self.inspect} and #{other.inspect} are not comperable") || 0
    end
  when String
    self.simple? && self.value <=> other
  else 1
  end
end

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

Returns true if this literal is equivalent to other (with type check).

Examples:

RDF::Literal(1) == RDF::Literal(1.0)     #=> true

Parameters:

  • other (Object)

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 320

def ==(other)
  case other
  when Literal
    case
    when self.eql?(other)
      true
    when self.direction? && self.direction == other.direction
      # Literals with directions can compare if languages and directions are identical
      self.value_hash == other.value_hash && self.value == other.value
    when self.language? && self.language == other.language
      # Literals with languages can compare if languages are identical
      self.value_hash == other.value_hash && self.value == other.value
    when self.simple? && other.simple?
      self.value_hash == other.value_hash && self.value == other.value
    when other.comperable_datatype?(self) || self.comperable_datatype?(other)
      # Comparing plain with undefined datatypes does not generate an error, but returns false
      # From data-r2/expr-equal/eq-2-2.
      false
    else
      type_error("unable to determine whether #{self.inspect} and #{other.inspect} are equivalent")
    end
  when String
    self.simple? && self.value.eql?(other)
  else false
  end
end

#canonicalize! ⇒ RDF::Literal

Converts this literal into its canonical lexical representation.

Subclasses should override this as needed and appropriate.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/model/literal.rb', line 523

def canonicalize!
  self
end

#compatible?(other) ⇒ Boolean

Term compatibility according to SPARQL

Compatibility of two arguments is defined as: * The arguments are simple literals or literals typed as xsd:string * The arguments are plain literals with identical language-tags and directions * The first argument is a plain literal with language-tag and the second argument is a simple literal or literal typed as xsd:string

Examples:

compatible?("abc"	"b")                         #=> true
compatible?("abc"	"b"^^xsd:string)             #=> true
compatible?("abc"^^xsd:string	"b")             #=> true
compatible?("abc"^^xsd:string	"b"^^xsd:string) #=> true
compatible?("abc"@en	"b")                     #=> true
compatible?("abc"@en	"b"^^xsd:string)         #=> true
compatible?("abc"@en	"b"@en)                  #=> true
compatible?("abc"@fr	"b"@ja)                  #=> false
compatible?("abc"	"b"@ja)                      #=> false
compatible?("abc"	"b"@en)                      #=> false
compatible?("abc"^^xsd:string	"b"@en)          #=> false

Returns:

See Also:

Since:

  • 2.0



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# File 'lib/rdf/model/literal.rb', line 255

def compatible?(other)
  return false unless other.literal? && plain? && other.plain?

  # * The arguments are simple literals or literals typed as xsd:string
  # * The arguments are plain literals with identical language-tags
  # * The first argument is a plain literal with language-tag and the second argument is a simple literal or literal typed as xsd:string
  language? || direction? ?
    (language == other.language && direction == other.direction || other.datatype == XSD_STRING) :
    other.datatype == XSD_STRING
end

#comperable_datatype2?(other) ⇒ Boolean

Returns true if the literals are comperable.

Used for <=> operator.

Returns:



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# File 'lib/rdf/model/literal.rb', line 502

def comperable_datatype2?(other)
  case self
  when RDF::Literal::Numeric, RDF::Literal::Boolean
    case other
    when RDF::Literal::Numeric, RDF::Literal::Boolean
      true
    else
      false
    end
  else
    self.datatype == other.datatype
  end
end

#comperable_datatype?(other) ⇒ Boolean

Returns true if the literal has a datatype and the comparison should return false instead of raise a type error.

This behavior is intuited from SPARQL data-r2/expr-equal/eq-2-2

Returns:



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# File 'lib/rdf/model/literal.rb', line 482

def comperable_datatype?(other)
  return false unless self.plain? || self.language?

  case other
  when RDF::Literal::Numeric, RDF::Literal::Boolean,
       RDF::Literal::Date, RDF::Literal::Time, RDF::Literal::DateTime
    # Invald types can be compared without raising a TypeError if literal has a language (open-eq-08)
    !other.valid? && self.language?
  else
    # An unknown datatype may not be used for comparison, unless it has a language? (open-eq-8)
    self.language?
  end
end

#datatype? ⇒ Boolean Also known as: has_datatype?, typed?, datatyped?

Returns true if this is a datatyped literal.

For historical reasons, this excludes xsd:string and rdf:langString

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 431

def datatype?
  !plain? && !language? && !direction?
end

#direction? ⇒ Boolean

Returns true if this is a directional language-tagged string.

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 420

def direction?
  datatype == RDF.dirLangString
end

#english? ⇒ Boolean

Returns true if this is a language-tagged literal in the English language.

Returns:

Since:

  • 3.3.2



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# File 'lib/rdf/model/literal.rb', line 460

def english?
  /\Aen(?:-[A-Za-z]{2})?\z/ === language.to_s
end

#eql?(other) ⇒ Boolean

Determins if self is the same term as other.

Examples:

RDF::Literal(1).eql?(RDF::Literal(1.0))  #=> false

Parameters:

  • other (Object)

Returns:



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# File 'lib/rdf/model/literal.rb', line 299

def eql?(other)
  self.equal?(other) ||
    (self.class.eql?(other.class) &&
     self.value_hash == other.value_hash &&
     self.value.eql?(other.value) &&
     self.language.to_s.eql?(other.language.to_s) &&
     self.direction.to_s.eql?(other.direction.to_s) &&
     self.datatype.eql?(other.datatype))
end

#escape(string) ⇒ String

Note:

N-Triples only requires ‘"nr’ to be escaped.

Escape a literal using ECHAR escapes.

ECHAR ::= ‘' [tbnrf“’]

Parameters:

  • string (String)

Returns:

  • (String)

See Also:



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# File 'lib/rdf/model/literal.rb', line 561

def escape(string)
  string.gsub('\\', '\\\\').
         gsub("\t", '\\t').
         gsub("\b", '\\b').
         gsub("\n", '\\n').
         gsub("\r", '\\r').
         gsub("\f", '\\f').
         gsub('"', '\\"').
         freeze
end

#hash ⇒ Integer

Returns a hash code for this literal.

Returns:



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# File 'lib/rdf/model/literal.rb', line 270

def hash
  @hash ||= [to_s, datatype, language, direction].compact.hash
end

#humanize(lang = :en) ⇒ String

Returns a human-readable value for the literal

Returns:

  • (String)

Since:

  • 1.1.6



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# File 'lib/rdf/model/literal.rb', line 585

def humanize(lang = :en)
  to_s.freeze
end

#inspect ⇒ String

Returns a developer-friendly representation of self.

Returns:

  • (String) 


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# File 'lib/rdf/model/literal.rb', line 593

def inspect
  sprintf("#<%s:%#0x(%s)>", self.class.name, __id__, RDF::NTriples.serialize(self))
end

#language? ⇒ Boolean Also known as: has_language?

Returns true if this is a language-tagged string.

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 410

def language?
  [RDF.langString, RDF.dirLangString].include?(datatype)
end

#literal? ⇒ Boolean

Returns true.

Returns:



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# File 'lib/rdf/model/literal.rb', line 228

def literal?
  true
end

#object ⇒ Object

Returns:

  • (Object) 


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# File 'lib/rdf/model/literal.rb', line 220

def object
  defined?(@object) ? @object : value
end

#plain? ⇒ Boolean

Returns true if this is a plain literal. A plain literal may have a language and direction, but may not have a datatype. For all practical purposes, this includes xsd:string literals too.

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 387

def plain?
  [
    RDF.langString,
    RDF.dirLangString,
    XSD_STRING
  ].include?(datatype)
end

#respond_to_missing?(name, include_private = false) ⇒ Boolean (protected)

Returns:



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# File 'lib/rdf/model/literal.rb', line 611

def respond_to_missing?(name, include_private = false)
  case name
  when :to_str
    return true if [RDF.langString, RDF.dirLangString, XSD_STRING].include?(@datatype)
  end
  super
end

#simple? ⇒ Boolean

Returns true if this is a simple literal. A simple literal has no datatype or language.

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 401

def simple?
  datatype == XSD_STRING
end

#squish(*other_string) ⇒ RDF::Literal

Returns the literal, first removing all whitespace on both ends of the value, and then changing remaining consecutive whitespace groups into one space each.

Note that it handles both ASCII and Unicode whitespace.

Returns:

See Also:



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# File 'lib/rdf/model/literal.rb', line 534

def squish(*other_string)
  self.dup.squish!
end

#squish! ⇒ Object

Performs a destructive #squish.

Returns:

  • self

See Also:



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# File 'lib/rdf/model/literal.rb', line 543

def squish!
  @string = value.
    gsub(/\A[[:space:]]+/, '').
    gsub(/[[:space:]]+\z/, '').
    gsub(/[[:space:]]+/, ' ')
  self
end

#to_s ⇒ String

Returns the value as a string.

Returns:

  • (String) 


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# File 'lib/rdf/model/literal.rb', line 576

def to_s
  @object.to_s.freeze
end

#valid? ⇒ Boolean

Returns true if the value adheres to the defined grammar of the datatype.

Returns:

Since:

  • 0.2.1



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# File 'lib/rdf/model/literal.rb', line 444

def valid?
  BCP47.parse(language.to_s) if language?
  return false if direction? && !%i{ltr rtl}.include?(direction)
  return false if datatype? && datatype.invalid?
  grammar = self.class.const_get(:GRAMMAR) rescue nil
  grammar.nil? || value.match?(grammar)
rescue BCP47::InvalidLanguageTag
  false
end

#validate! ⇒ RDF::Literal

Validates the value using Value#valid?, raising an error if the value is invalid.

Returns:

Raises:

  • (ArgumentError) —

    if the value is invalid

Since:

  • 0.2.1



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# File 'lib/rdf/model/literal.rb', line 471

def validate!
  raise ArgumentError, "#{to_s.inspect} is not a valid <#{datatype.to_s}> literal" if invalid?
  self
end

#value ⇒ String

Returns the value as a string.

Returns:

  • (String) 


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# File 'lib/rdf/model/literal.rb', line 214

def value
  instance_variable_defined?(:@string) && @string || to_s
end

#value_hash ⇒ Integer

Returns a hash code for the value.

Returns:



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# File 'lib/rdf/model/literal.rb', line 279

def value_hash
  @value_hash ||= value.hash
end